By RIZWAN ULLAH INSTITUTE OF CHEMICAL SCIENCES...

SYNTHESIS AND CHARACTERIZATION OF

POLYANILINE CO-DOPED WITH POLYVINYL

ALCOHOL AND TRANSITION METALS

Ph.D Thesis

By

RIZWAN ULLAH

INSTITUTE OF CHEMICAL SCIENCES

UNIVERSITY OF PESHAWAR PAKISTAN

(OCTOBER, 2014)

SYNTHESIS AND CHARACTERIZATION OFPOLYANILINE CO-DOPED WITH POLYVINYL

ALCOHOL AND TRANSITION METALS

BY

RIZWAN ULLAH

DISSERTATION

SUBMITTED TO THE UNIVERSITY OF PESHAWAR IN THE PARTIALFULFILLMENT OF THE REQUIREMENTS OF THE DEGREE OF

DOCTOR OF PHILOSPHY IN CHEMISTRY


UNIVERSITY OF PESHAWAR PAKISTAN

(OCTOBER, 2014)


UNIVERSITY OF PESHAWAR, PAKISTAN

APPROVAL SHEET

Certified that Mr. Rizwan Ullah S/O Shakir Ullah has carried out his research and experimental

work on the topic entitled as “Synthesis and Characterization of Polyaniline Co-Doped with

Polyvinylalcohol and Transition Metals” under our guidance and supervision. His research

work is original and his dissertation is worthy of presentation to the University of Peshawar for

the award of degree of Doctor of Philosophy in Chemistry.

______________________ _______________________

SUPERVISOR CO-SUPERVISOR

Prof. Dr. Khurshid Ali Dr. Anwar-Ul-Haq Ali Shah

Institute of Chemical Sciences, Institute of Chemical Sciences,

University of Peshawar, Pakistan University of Peshawar, Pakistan

_________________________ _______________________

Dr. YOUSAF IQBAL EXTERNAL EXAMINAR

Professor & Director

Institute of Chemical Sciences,

University of Peshawar Pakistan

i

Dedication

To my teachers & my mentors

Prof. Dr. Khurshid Ali and Dr. Anwar-Ul-Haq Ali Shah

Without whom this work would never have come into being.

To those flanking to me

My Parents, My Brothers, My Sisters & My Wife

Whose love, patience, support and encouragement stay with

me throughout my life.

To my Lovely Daughter

Fatima Aiman

Whose love is priceless to me and will always endure me.

ii

Acknowledgements

All praise to Allah the Omniscient, who thought man what, he not knew, who equipped

his humble creature with mental facility, which enabled and encouraged me to complete

this work. Peace and blessing be upon Prophet Muhammad Salallaho Alaihy Wasallam,

his families, his relatives and all his followers.

A single flower cannot make a garden or a single star cannot make the beautiful shiny

sky. The same way a research work can never be the outcome of a single individual‘s

talent or effort. During my trip from objective to goal, I have experienced shower of

blessings, guidance and inspiration from my teacher’s parents and all my well-wishers.

Though it is not possible for me to name and thanks them all individually, but it is great

pleasure for me to pen down some of the distinct personalities who have made it

possible for me to put this research work in present form.

First and foremost, I take this opportunity to express my profound sense of gratefulness

to my venerated guide, mentor and my research supervisor, Prof. Dr. Khurshid Ali

whose flawless guidance, boundless enthusiasm, persevering nature, enlightening

discussion and valuable suggestion have enabled me to complete this work. Only

because of his support and inspiration I could confidently embark upon a research work

of such magnitude. I consider myself fortunate to have had the opportunity to work

under his guidance.

iii

I would like to express my deep sense of gratitude to Dr. Anwar –Ul-Haq Ali Shah

(Associate Professor); my research co-supervisor who encouraged me and who has

shown keen interest in my assignment and has inspired me and render self less support

throughout this investigation. I appreciate all his contributions of time and ideas to make

my Ph.D. experience productive and inspiring. The joy and enthusiasm he has for

research work was contagious and motivational for me.

I am truly grateful to both of them. I can’t thank them enough, but I pray Allah, to bless

them for their exertions and reward them according to His generosity.

I would also like to acknowledge the contributions, advice and suggestions of my foreign

supervisors Dr. Jadranka Travas Sejdic and Prof. Dr. Graham A. Bowmaker who

supported me during the six month research at the Polymer Electronic Research Centre

(PERC) University of Auckland, New Zealand.

I gratefully acknowledge the Higher Education Commission of Pakistan for financial

support and providing me a tremendous opportunity to complete my research work at

the Institute of Chemical Sciences, University of Peshawar through Indigenous Ph.D

Fellowship Program and at the Polymer Electronic Research Centre (PERC) University

of Auckland, New Zealand, through International Research Support Initiative Program.

Mention must be made of my worthy professors and teachers at the Institute of

Chemical Sciences who have helped me in various ways. For this, I am truly blessed.

iv

I would like to express my sincere thanks to Dr. Yousaf Iqbal., Professor and Director

Institute of Chemical Sciences University of Peshawar, for the support he gave me

along the way.

Very special thanks and my deep gratitude go to Dr. Sher Khan, Moeen Ul Amin,

Ahmad Bilal, Umar Javed, Waseem Ahmad, Azan Meer, and Mohy Uddin Khan Khattak

for their support during my stay at Newzealand.

I would like to thank Dr. Habib-Ur-Rehman, Dr. Fazlullah Khan Banghash and Dr. Atta-

Ur-Rehman teaching faculty member of physical section, for their support during my

work. I want to extend my special thanks to Dr. Salma Bilal for providing me help and

support in my work.

I am grateful to my senior scholar colleagues for providing a stimulating and decent

environment to learn and grow. Many thanks to Dr. Inayatullah, Dr. Nasir Ullah, Dr.

Hamid Hussain, Dr. Abdul Hameed, Dr. Andaleeb Azam and Dr. Behisht Ara.

My time at the institute was made enjoyable in large part due to my colleagues and

friends. I am grateful to Mr. Muhammad waqas, Mr. Imran Ullah, Ms. Shanaz Pir

Muhammad, Ms. Aliya, Ms. Robila Nawaz, and Ms. Saima Shaheen. I cannot forget

Habib Ullah and Amir Muhammad who were always around me in my hard times.

I take this opportunity to acknowledge with thanks the help and support that I have

received from Mr. Ashfaq (Librarian ICS), Mr. Zaheer ud Din (store supervisor), Mr.

v

Muhammad Ali, Mr. Arif Ismail, Mr. Jangir Khan, Mr. Ilyas Khan, Mr. Sajid Khan and all

the clerical and para teaching staff of Institute of Chemical Sciences.

I want to express my sincere gratitude to my great father and mother who suffered a lot

to keep me free from domestic responsibilities and their prayers, guidance, and sound

advice have inspired and sustained me throughout my academic and personal life. I pay

a profound appreciation to my brothers; Zakir Hussain and Muhammad Fawad, to my

humble and simple sisters, to my uncle, Gulzar Ahmad, and of course my sweet and

lovely daughter Fatima Aiman whose love is invaluable to me and will always sustain

me. I love you all!

Words fail to express the endurance with which my loving wife bore my absence. She

offered determined patience, love, support and confidence in me, for which there is no

adequate way to express my appreciation.

Last but not least, I owe gratitude and thankfulness to all who were involved directly or

indirectly, knowingly or unknowingly to reach in the venture of mine.

Rizwan Ullah

University of Peshawar

October 2014

vi

Table of Contents

S.No Title P. No.

Dedication i

Acknowledgment ii

Table of content vi

List of tables xi

List of figures xii

List of abbreviations xv

List of publications xviii

Abstract xix

1 CHAPTER 1. INTRODUCTION 1

1.1 Literature review 2

1.2 Polyaniline 11

1.2.1 Structure of Polyaniline 11

1.2.2 Conductivity of polyaniline (PANI) 12

1.2.3 Mechanism of Conductivity 13

1.2..4 Synthesis of Polyaniline (PANI) 15

1.2.5 Mechanisms of polymerization 16

1.2.6 Doping of PANI 18

1.3 Characterization of PANI 19

1.3.1 UV/Visible spectroscopy 19

1.3.2 FTIR spectroscopy 20

1.3.3 X-ray diffraction (XRD) 20

1.3.4 Cyclic voltammetry 21

1.3.5 Scanning electron microscopy (SEM) 22

1.3.6 Elemental analysis 22

1.4 Solubility of PANI 23

1.5 Polymerization of substituted aniline 24

1.5.1 Copolymerization of aniline 24

vii

1.5.2 PANI blends 25

1.5.3 PANI doped with surfactants 25

1.5.4 Composites of PANI 26

1.6 Aims and objectives of the work 26

2 CHAPTER 2. EXPERIMENTAL 28

2.0 Experimental (Part I) Synthesis and Characterization of Polyanilineby using CuCl2 as Oxidizing agent

28

2.1 Materials 28

2.2 Procedure 28

2.3 Dedoping of B-PANI and H-PANI 29

2.4 Reduction of PANI, DB-PANI and DH-PANI 29

2.5 Characterization 29

2.5.1 FTIR Spectroscopy 29

2.5.2 UV/Vis Spectroscopy 30

2.5.3 Elemental Analysis 30

2.5.4 X-ray Photoelectron Spectroscopy (XPS) 30

2.5.5 Near Edge X-ray Absorption Fine Structure (NEXAFS)

Spectroscopy

30

2.5.6 Solid-state NMR 31

2.5.7 SEM analysis 31

2.6 Experimental (Part II) Synthesis and characterization of

leucoemeraldine

31

2.6.1 Materials 31

2.6.2 Procedure 31

2.6.3 Characterization 32

2.6.3.1 FTIR Spectroscopy 32

2.6.3.2 UV/Vis Spectroscopy 32

2.6.3.3 Elemental Analysis 32

2.7 Experimental (Part III) Synthesis and characterization of polyanilinedoped with Cu II chloride by inverse emulsion polymerization

33

viii

2.7.1 Materials 33

2.7.2 Procedure 33


2.7.3.1 Conductivity measurements 33

2.7.3.2 UV/Vis spectroscopy 34

2.7.3.3 FTIR spectroscopy 34

2.7.3.4 Thermo gravimetric analysis (TGA) 34

2.7.3.5 X-ray diffraction (XRD) 34

2.7.3.6 Scanning electron microscopy 34

2.7.3.7 Cyclic voltammetry 34

2.8 Experimental (Part IV) Synthesis and Characterization of

Polyaniline Doped with Polyvinylalcohol by Inverse Emulsion

Polymerization

35

2.8.1 Materials 35

2.8.2 Procedure 35


2.8.3.1 Conductivity measurements 36



2.8.3.4 Thermo gravimetric analysis 36

2.8.3.5 X-ray diffraction (XRD) measurements 36

2.8.3.6 Scanning electron microscopy (SEM) 36

2.8.3.7 Cyclic voltammetry 37

2.9 Synthesis and Characterization of Polyaniline Co-doped withPolyvinylalcohol and Cu by Inverse Emulsion Polymerization

37

2.9.1 Material 37

2.9.2 Procedure 37

ix


2.9.3.1 Conductivity and mass measurement 38



2.9.3.4 Thermo gravimetric analysis 38

2.9.3.5 X-ray diffraction 38

2.9.3.6 Scanning electron microscopy 38

2.9.3.7 Cyclic Voltammetry 39

3 CHAPTER 3. RESULTS AND DISCUSSION 40

3.1 pH measurement and mass yield calculations 40

3.2 FTIR Spectroscopy 42

3.3 UV/Vis Spectroscopy 45

3.4 Elemental Analysis 47

3.5 X-Ray Photoelectron Spectroscopy 48

3.6 Soft X-ray Spectroscopy 53

3.7 Solid state NMR 54

3.8 SEM analysis 56

3.9 Mechanism of PANI fabrication 57

3.10 Results and discussion Part (II) 58

3.11 pH measurements and along with mass yield 58


3.13 UV/Vis Spectroscopy 59

3.14 Elemental Analysis 60

3.15 Results and discussion (Part III) 61

3.16 Mass yield and conductivity measurements 61

3.17 UV/Visible spectroscopy 61

3.18 FTIR spectroscopy 62

3.19 Thermogravimetric analysis (TGA) 63

3.20 X-ray diffraction (XRD) 64

x

3.21 Scanning electron microscopy (SEM) 65

3.22 Cyclic voltammetry (CV) 66

3.23 In situ UV/Vis spectroscopy 67

3.24 Results and discussion (Part IV) 71

3.25 Conductivity measurements and mass yield 71

3.26 UV/Visible spectroscopy 72

3.27 FTIR spectroscopy 72

3.28 Thermo gravimetric analysis (TGA) 73

3.29 X-ray diffraction (XRD) 74

3.30 Scanning electron microscopy (SEM) 75

3.31 Cyclic voltammetry (CV) 76

3.32 In situ UV/Visible Spectroscopy 77

3.33 Results and Discussion (Part V) 81

3.34 Conductivity Measurements and Mass Yield 81

3.35 UV/Visible Spectroscopy 82


3.37 Thermo gravimetric Analysis (TGA) 83

3.38 X-Ray Diffraction 84

3.39 SEM Analysis 86

4 CHAPTER 4. CONCLUSION 88

REFERENCES 91

xi

List of Tables

Table No. Table caption P. No.

1

Initial and Final Solution pH and Mass Yields for Reactionswith Various Oxidant to Monomer Ratios R

40

2

Weight (%) Loss of B-PANI after washing with HCl, NH4OHand N2H4 and corresponding Mass Yield of H-PANI, DB-PANIand PANIa 41

3

Compositions of DB-PANI and H-PANI for oxidant tomonomer ratio R = 15

48

4

Speciation of Nitrogen in PANI samples from N 1s PeakAnalysis

53

5

Peak assignment in the SSNMR of EB form of PANI

55

6

Oxidant to Monomer Ratio and Mass Yield along with initialand final pH

58

7

Elemental Analysis Results of L-PANI

60

8

Mass Yield and Conductivity of PANI and its Composites withCu

61

9

Mass Yield and Conductivity of PANI and its Composites withPVA

71

10

Mass Yield and Conductivity Measurements

81

xii

List of Figures

Fig. No. Figure caption P. No.

1Various redox states of PANI

12

2Interconversion of emeraldine base and emeraldine salt

13

3Radical cation formation and its resonance stabilization

16

4Conversion of radical cation to para-aminodiphenylamine

17

5Acid doping of PANI

18

6X-rays diffraction in a crystalline material

21

7FTIR spectrum of the initial product (R = 15) before washing

42

8

FTIR spectra of A(a) B-PANI, (b) H-PANI(c) PANI, B(a) DB-

PANI and (b) RB-PANI, C(a) PANI and (b) R-PANI, D(a) DH-

PANI and (b) RH-PANI.

43

9

UV/Vis spectra of A(a) B-PANI, (b) H-PANI, (c) PANI, B (a)DB-PANI (b) RB-PANI, C(a) PANI, (b) R-PANI, D(a) H-PANI,(b) DH-PANI and (c) RH-PANI

46

10Cu 2p XPS for (a) H-PANI, and (b) DB-PANI.

50

11N 1s XPS for (a) H-PANI, and (b) DB-PANI

52

12NEXAFS of (a) B-PANI (b) DB-PANI (c) RB-PANI

54

13

13C Solid State NMR spectra of DH-PANI55

14SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI

56

15Mechanism of PANI formation

57

16FTIR spectra of (a) pure EB (b) L-PANI

59

17UV/Vis spectra of (a) pure EB (b) L-PANI

60

18

UV/Vis spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4,(d) PANI-Cu 0.6 and (e) PANI-Cu 0.7

62

xiii

19

FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4,and (d) PANI-Cu 0.6.

63

20TGA analysis of (a) PANI (b) PANI-Cu

64

21XRD analysis of (a) PANI and (b) PANI-Cu

65

22SEM images of (a) PANI and (b) PANI-Cu

66

23CVS of (a) PANI and (b) PANI-Cu

67

24

UV-Vis spectra of (a) PANI and (b) PANI-Cu film, deposited onITO coated glass electrode, obtained at different electrodepotential values ranging from ESCE= 0.0 TO 0.8 V at an intervalof 0.1 V 68

25

(a) and (b) Absorbance vs. Potential at three selectedwavelengths, derived from the above displayed spectra in Fig. 24(a) and (b) 70

26UV/Vis spectra of (a) PANI and (b) PANI/PVA.

72

27FTIR spectra of (a) PANI and (b) PANI/PVA

73

28TGA curve of (a) PANI and (b) PANI/PVA

74

29XRD of (a) PANI and (b) PANI/PVA

75

30SEM images of (a) PANI and (b) PANI/PVA

76

31

CVs of (a) PANI and (b) PANI/PVA on gold foil electrode (vsSCE) in 0.5M H2SO4

77

32

UV/Vis spectra of (a) PANI and (b) PANI/PVA film, depositedon ITO coated glass electrode, obtained at different electrodepotential values ranging from ESCE= 0.0 TO 0.8 V at an intervalof 0.1 V 78

33

(a) and (b) Absorbance vs. Potential at three selectedwavelengths, derived from the above displayed spectra in Fig 32.(a) and (b). 80

34

UV/Vis spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and(d) PANI-Cu-PVA

82

35

FTIR spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA

83

36TGA analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 84

xiv

37XRD analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 85

38SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d)PANI-Cu-PVA 87

xv

LIST OF ABBREVIATIONS

% Percent

oC

cm-1

Degree celsius

Per centimeter

µm

γ

Micrometer

Gamma

µgL-1 Microgram per milliliter

APS Ammoniumpersulfate

AuNPs

β-NSA

BPO

CNT

Gold nanoparticles

Betanephthalensulfonic acid

Benzoyl peroxide

Carbon nanotubes

CSA Camphorosillinic acid

CV Cyclic voltammetry

cm Centimeter

DI Deionized water

DBSA

EB

Dodecylbenzenesulfonic acid

Emeraldine base

EDX

EIS

Energy dispersive x-ray spectroscopy

Electrochemical Impedance Spectroscopy

ES

FTIR

Emeraldine salt

Fourier transformed infrared spectroscopy

g Gram

g/mol Gram per mole

xvi

kV Kilo volt

LE Leucoemeraldine

L mol-1 cm-1 Liter per mol per centimeter

mg Milligram

mgL-1 Milligram per milliliter

mgL-1 Milligram per liter

mL Milliliter

MS Mass spectrometry

min Minute

M Molarity

molL-1 Mole per liter

mm Millimeter

mV Milli volt

mmolL-1 Milli mole per liter

µM Micromolar

µgL-1 Microgram per liter

µm Micrometer

µg cm-2

NEXAFS

NDR

Microgram per centimeter squareNear edge x-ray absorption fine structurespectroscopy

Negative differential resistance

nm Nanometer

PAA Polyacrylic acid

PANI

PANI-CSA/Au

Polyaniline

Polyaniline-camphorosillinic acid/gold

PANI/Cu Polyaniline/copper

xvii

PANI/Cu/PVA

PANI-p-TSA/Au

Polyaniline/Copper/Polyvinylalcohol

Polyaniline-paratoluenesulfonic acid-gold

PANI/PVA

PN

PPY

PSSA

Polyaniline/Polyvinylalcohol

Pernigraniline

Polypyrrole

Polystyrene sulfonic acid

PTSA

PVA

Paratoluenesulfonic acid

Polyvinyl alcohol

RP Reversed Phase

S cm-1 Siemens per centimeter

SDS Sodium dodecyl sulfate

SSNMR Solid state nuclear magnetic resonancespectroscopy

TGA Thermo gravimetric analysis

TEM Transmission electron microscopy

UV/ Vis Ultra violet visible spectroscopy

V Volt

XPS

XRD

X-ray photoelectron spectroscopy

X-ray diffraction spectroscopy

xviii

List of Publications

1. Rizwan Ullah, Graham A. Bowmaker, Khurshid Ali, Anwar-Ul-Haq Ali Shah*, Jadranka

Travas-Sejdic. Synthesis and Characterization of Polyaniline by Using Weak Oxidizing

Agent. Macromolecular symposia 2014, 339, 84-90.

2. Rizwan Ullah, Khurshid Ali, Salma Bilal, Anwar-ul-Haq Ali Shah*. Synthesis and

Characterization of Polyaniline Doped with Cu II Chloride by Inverse Emulsion

Polymerization. Synthetic metals 198 (2014) 113-117.

3. Rizwan Ullah, Graham A. Bowmaker*, Cosmin Laslau, Geoffrey I.N. Waterhouse, Zoran

D. Zujovic, Khurshid Ali, Anwar-Ul-Haq Ali Shah, Jadranka Travas-Sejdic. Synthesis of

Polyaniline by using CuCl2 as Oxidizing Agent. Synthetic Metals (Article in press)

4. Rizwan Ullah, Khurshid Ali, Muhammad Sadiq Afridi, Anwar-ul-Haq Ali Shah*. Synthesis

and characterization of leucoemeraldine form of Polyaniline by using weak oxidizing agent.

Polymer (Under review).


Characterization of Polyaniline Doped with Polyvinylalcohol by Inverse Emulsion

Polymerization (To be submitted to Synthetic metals).


Characterization of Polyaniline Co-Doped with Polyvinylalcohol and Cu II Chloride by

Inverse Emulsion Polymerization (In preparation to Synthetic metals).

xix

ABSTRACT

The synthesis of polyaniline (PANI) and its composites with transition metals like Cu and

polyvinyl alcohol (PVA) was carried out by the chemical oxidative polymerization and inverse

emulsion polymerization method of aniline. The samples were characterized by UV/Vis, FT-IR,

XPS, NEXAFS, and SSNMR. Elemental analysis was carried out to calculate the composition

of products. SEM images were taken to study the morphology of PANI and its composites. TGA

and XRD data was collected to study the thermal properties and crystallinity of the resulting

PANI and its composites. Cyclic voltammetry and conductivity measurement were carried out to

check the electro activity and conductivity of PANI and its composites. The UV/Vis, FT-IR,

XPS, NEXAFS and SSNMR and elemental analysis showed that polyaniline was formed in a

partially oxidized form, partially protonated, and doped with [CuCl3]- as the counter ion. Low

concentration of weak oxidant results in the formation of leucoemeraldine form of PANI. SEM

results show the spherical morphology of PANI particles doped with [CuCl3]-.

In case of co-composites of PANI with PVA and copper a smooth morphology was observed

from the SEM images as compared to the irregular morphology of PANI-PVA and PANI-Cu

obtained by inverse emulsion polymerization. The XRD and TGA confirm the amorphous nature

and an improved thermal stability of composites. CV analysis shows that PANI and its

composites are electroactive. The composites of PANI have better conductivity in comparison to

PANI as shown by conductivity measurement.

1

1. INTRODUCTION

1. Introduction

A conducting polymer is a system which possesses π-conjugated electrons for the

transport of electric current. Generally, the traditional polymers are considered to be insulators

and used in the electronic industries due to the insulating properties, whereas the conducting

polymers are semiconductors and have the ability to be doped to show metal like conductivity.

The use of conducting polymer gained tremendous importance soon after the discovery of

polyacetylene by Shirakawa [1] in 1975. A large variety of the conducting polymers are

available as a result of tremendous amount of research efforts in the field of conducting

polymers. Among the most promising types of conducting polymers, discovered by scientists,

polypyrrole, polyethylene, polythiophenes, polyphenylenevinylene, and polyaniline etc are worth

mentioning [2]. Since these materials showed some metallic properties so they were also named

as “synthetic metals”[3]. This new class of organic polymers shows important properties like low

density, resistance to corrosion, good environmental stability, high conductivity and low cost of

synthesis. The conducting polymers have a metal like optical and electrical properties,

mechanical flexibility with ease of processing, leading to the discovery of new innovative

devices and applications in the field of conducting polymers [4, 5]. The tuning of morphology of

the conducting polymers to the nanoscale by designing their dimensions often gives new

properties [6]. Examples of such properties are increased strength, greater conductivity,

molecular ordering and improved reactivity due to the large surface area [7, 8]. Conducting

polymers in combination with inorganic nanoparticles of variable size and shape give rise to new

composite materials with different physical and chemical properties thereby generating

possibilities for fascinating applications [9]. Conducting polymer blends are also studied in

2

recent years because of their significant importance in basic and applied sciences. Many devices

can be designed due to the fusion of interesting electronic, mechanical and optical properties

[10]. Conducting polymers in general are insoluble in common solvents and are infusible in

nature, thus the conventional blending techniques are not suitable for the formation of

nanocomposites, therefore, synthetic methods and techniques are to be designed to incorporate

the inorganic component into the conducting polymers. Unlike the conventional nanocomposites

where the flexibility and improved processibility for the system is provided by the polymer, the

inorganic nanoparticles are responsible for the processibility of conducting polymers [11].

1.1 Literature review

The optical, electrochemical, and electronic properties of polyaniline (PANI) drew the

attention of scientists to investigate this polymer for further applications. Moreover, the use of

PANI in light emitting diodes, electro-optics, light-weight batteries, sensors, anti-corrosion

coatings, bio capacitors and electromagnetic shielding materials has given commercial

importance to PANI [12-15]. In recent years PANI nanocomposites are gaining importance due

to new practical applications [16].

Sejdic et al. [17] successfully synthesize Polyaniline-paratoluenesufonicacid/gold (PANI-

p-TSA/Au) composite by using gold chloride trihydrate as an oxidizing agent. For the purpose of

comparison they also prepared samples by using ammoniumpersulfate (APS) as an oxidizing

agent. The samples were characterized by using SEM, TEM, FTIR, XRD, XPS and Raman

spectroscopy. The SEM images showed the spherical morphology of the composites rather than

the fibrous as in the case of APS as an oxidant. One of the reasons for the spherical morphology

reported in this work is the lower oxidation potential of gold chloride (0.994 V) as compared to

3

APS (2.0 V) due to which the kinetics of the reaction is slower thereby preventing the elongation

of chain. The second reason is the formation of elemental gold during the course of reaction

which hinders the elongation process of nanosphers to nanotubes. The TEM and XRD studies

confirmed the presence of Au particles decorated on the spheres. Significant changes were

observed in the FTIR and Raman spectra of the composites prepared by using APS and gold

chloride as oxidizing agents. The conductivity of PANI-p-TSA/Au composite is higher than the

PANI-p-TSA nanofibers at room temperature.

Wan et al. [18] prepared PANI fibers by replacing APS with FeCl3 as an oxidizing agent

in the presence of p-TSA, betanephthalensulfonic acid (β-NSA) and camphorosillinic acid

(CSA). For the purpose of comparison they also prepared samples by using APS as oxidizing

agent and found that the PANI doped with CSA, p-TSA and β-NSA in the presence of FeCl3 as

oxidizing agent have smaller diameter(10-30 nm), more conducting and has high crystallinity

than those prepared in the presence of APS. They concluded that FeCl3 is an ideal oxidant to

prepare nanoscale PANI fibers by the template free method.

Polyaniline/gold composites were chemically synthesized by Hatchett [19] and his co-

workers using tetrachloroaurate as oxidizing agent and reported large yield of reaction. They

carried out the in-situ UV/Vis spectroscopy and reported that gold colloids and short chains are

formed with a faster rate as compared to the long chain PANI. A polymer/metal composite is

formed as a result of metal encapsulation by the polymer. The resulting composites of PANI/Au

were characterized by using FTIR, XPS, and TEM. The results obtained from FTIR for PANI

were in agreement with the preparation of PANI in the presence of ammoniumpersulfate (APS).

Polycrystalline gold particles were shown by XPS and TEM with a diameter of 0.8-1 µm. From

4

the conductivity measurements they concluded that no significant change in the conductance

occurs by the encapsulation of Au in the composite.

Bertino et al. [20] synthesized the polyaniline-metal nano composite by passing γ

radiations from the aqueous solution of aniline containing a metal salt like silver nitrate and gold

chloride. The main advantage of this method is that it does not require large amounts of organic

solvents and the morphology of polyethylene fibers does not change with the addition of water

soluble salt in the aqueous solution of aniline. The synthesized nanocomposites were subjected to

TEM analysis which shows that the polyaniline fibers have a diameter of 50-100 nm. The length

of fiber varies from 1-3 µm. The metal particles were decorated on the fibers. The particle size of

metal increases with an increase in concentration of metal with respect to aniline concentration.

Several micrometers long dendritic structures were obtained when the concentration ratios of

aniline to metal is close to 1:1. The reports from XRD also confirm the presence of metal

particles by showing sharp peaks at (111), (200), (220), and (310) Bragg reflection of gold and

silver. The FTIR spectra show the characteristic peaks of benzenoid and quinoid rings of

polyaniline at 1490 cm-1 and 1570 cm-1 respectively. In the same study they concluded that

benzoyl peroxide (BPO) is a good oxidizing agent as compared to ammoniumpersulfate because

the purity of the final product is highly affected by the oxidizing agent. In case of BPO the by-

products were removed easily as compared to ammoniumpersulfate (APS).

The polyaniline/gold composites were synthesized in the presence of camphorsulfonic

acid (CSA) and hydrochloric acid (HCl) as dopant by Zhu et al. [21]. They prepared PANI doped

with HCl, PANI doped with CSA, PANI-HCl/Au composite and PANI-CSA/Au composite.

These samples were characterized by FTIR, UV/Vis and TGA to find out the incorporation of

Au. The structural morphology was examined by SEM, TEM and XRD techniques. The PANI-

5

CSA/Au composite have tubular morphology with a diameter ranging from 170-300 nm. On the

walls of the nano tubes Au particles appear as dark spots. The SEM image shows the overlap of

fibers and having a net like structure confirming that the morphology is predominantly nano

fibrous. From the XRD data they reported that HCl-doped PANI is amorphous and CSA-doped

PANI is comparatively more crystalline than HCl-doped PANI which is attributed to the

different molecular sizes. Due to the incorporation of gold in the PANI-HCl and PANI-CSA

composites new peaks appear in the XRD confirming the crystallinity of composites. In the FTIR

spectra a reasonable shift in peaks to the lower wavelength is observed due to presence of Au in

the composites. The reported reason is that Au is electron donating, which further delocalizes the

electron density of PANI. The TGA data confirm the incorporation of greater amount of Au in

PANI-CSA/Au composite as compared to PANI-HCl/Au composite which may be attributed to

the adsorption interaction of Au and CSA. From the conductivity measurements they concluded

that PANI-CSA/Au composites have more conductivity than PANI and PANI-HCl/Au

composite. Three reasons for greater conductivity of PANI-CSA/Au composite are reported.

First is the greater content of Au, second the more crystalline and third is the increase in doping

level of PANI-CSA/Au composite. The three reasons were supported by TGA, XRD and UV/Vis

spectroscopy.

Wang et al. [22] has carried out one-step synthesis of polyaniline/gold core shell

particles. They reported the use of chlorauric acid as an oxidizing agent in acidic media of acetic

acid and tween 40. The reactions were carried out at room temperature. The samples were

characterized by UV/Vis, SEM, TEM, and XRD. The SEM results show that the gold particles

are covered by the polymer layer. The XRD results confirmed the presence of gold particles in

the core shell. In the presence of acetic acid different sized PANI micro rods are formed but

6

when acetic acid was replaced by distilled water then only PANI-Au composites were formed.

From this result they concluded that acetic acid is good solvent as compared to distilled water for

the solubility of both aniline and tween 40. TEM results show the formation of micelles. This

study reveals that acetic acid is a good solvent and tween 40 is a good surfactant for the

solubility of aniline.

Wei et al. [9] proposed a one-step process for the electrochemical fabrication of an air-

stable memory device based on PANI and gold particles. They synthesized the composite

material by cyclic voltammetry at room temperature. The gold particles were found to be

distributed in the PANI matrix. The resulting composite shows that the negative differential

resistance (NDR) was repeatable even after 8 weeks exposure to air thus pave the way to use the

material in printable electronics.

Periodic acid H5IO6 was used by Muzaffer Can et al. [23] as an oxidant for the chemical

polymerization of aniline in anhydrous medium. For the chemical synthesis of conducting

polymer this is the first time that H5IO6 has been used. For the characterization of product they

used UV-Visible, FTIR spectroscopy, scanning electron microscopy (SEM), thermo gravimetric

analysis (TGA), energy dispersive x-ray (EDX) spectroscopy and electrical conductivity

measurements. The results obtained from EDX and thermo gravimetric analysis indicated the

presence of ClO-4 and iodine or iodide ion as dopant. The doping of aniline by I2 was preceded

by oxidation with IO-3 produced from H5IO6. In this work there is no residual contamination of

oxidant. In this study the extrinsic dopant I2 was produced intrinsically from H5IO6 after the

formation of IO-3. Thus for the chemical polymerization of aniline, H5IO6 was found to be a very

useful oxidative agent.

7

The amperometric detection of organophosphate was studied by Du et al. [24]. They

designed an acetyl cholinesterase biosensor in which the carbon nanotubes (CNTs) are

encapsulated into the copolymer of PANI and polypyrrole. The resulting composite was

characterized by FTIR and SEM. The electrochemical behavior was studied with the help of

electrochemical impedance spectroscopy (EIS). The biosensor being small in size shows

excellent sensitivity, high selectivity, good long-term stability, fast response, good

reproducibility and low cost of synthesis. This has opened the way to analyze the pesticides and

characterize the enzyme inhibitor by an environmental friendly tool as it does not involve the use

of any toxic agent.

The anticorrosive properties of pure PANI and its nanocomposites with clinoptilolite

(zeolite mineral) were investigated by Olad et al. [16]. The PANI samples were synthesized by

common oxidation process. The clinoptilolite were prepared from its grinded rocks in 1M HCl

solution. The PANI-clinoptilolite composites were synthesized by the chemical oxidation

method with 1%, 3% and 5% clinoptilolite by weight. The resulting composites were

characterized by FTIR, XRD and SEM. The cyclic voltamograms were recorded in 1 M H2SO4,

1 M HCl, and 1 M NaCl. The results show that the corrosion current of 3% PANI-Clinoptilolite

is less than that of pure PANI and PANI-Clinoptilolite containing 1% and 5% clinoptilolite.

Li et al. [25] prepared PANI doped with different concentrations of hydrochloric acid.

The samples were characterized by SEM, FTIR, XRD and TGA. They proposed that the

conductivity and thermoelectric properties of PANI first increase and then decrease as a function

of hydrochloric acid concentration.

8

The doping of polymeric acids like polystyrene sulfonic acid (PSSA), polyacrylic acid

(PAA) and poly methyl vinyl ether-alt-maleic acid (PMVEA) on polyaniline was carried out by

Zhang et al. [26] in the presence of ammonium persulfate as oxidizing agent and reported that

the structural morphology and size of resulting composite is greatly affected by the molecular

structure of polymeric acid. The samples were characterized by SEM, FTIR and electron

paramagnetic resonance (EPR) spectroscopy. They concluded that the outer diameter of PANI-

PSSA is larger as compared to PANI-PAA and PANI-PMVEA. The larger diameter is attributed

to the presence of a bulky benzene ring and sulphonic acid group. They further concluded that

the presence of polymeric acid on the PANI provides more sites for other functional groups to be

attached for making sensing devices.

Nuraje et al. [27] synthesized single crystalline nano needles of polypyrrole (PPY) and

polyaniline (PANI) by using interfacial polymerization. The TEM images show the rice like

structures of PANI with dimensions of 63nm×12nm and PPY of dimensions 70nm×20nm. The

needles were shown to be crystalline and conductive. The degree of crystallization can be

increased by the increase in crystallization time at the interface. This method has the advantage

of making single crystalline nano crystals while the other interfacial polymerization methods

lead to non-crystalline polymer fibers.

Gupta and co-workers [5] prepared polyaniline-silver nanocomposites to study their

optical and electrical transport properties. The samples were synthesized by the chemical

oxidation polymerization method by using ammoniumperoxidisulfate as an oxidizing agent in

the presence of negatively charged silver nanoparticles. The samples were characterized by

SEM, TEM, TGA, XRD, and FTIR etc. From the SEM and TEM analysis it appears that the

polymer matrix has metal particles dispersed in it. The XRD shows the crystalline nature of the

9

PANI-Ag nanocomposites. The thermal stability of the composite material is greater as

compared to PANI. The electrical conductivity of the composites increases with increase in

concentration of metal. The photoluminescence of the composite material is greater in

comparison to PANI.

In another study Gupta et al. [28] synthesized the composite of polyaniline nano-rods

with copper chloride. The chemical oxidation polymerization was carried out by using

ammonium persulfate as oxidizing agent. The SEM images show rod like structures. The average

diameter of the nano rods was found to be 80 nm and length of about 2-3 µm. The XRD pattern

shows that the composite material has monoclinic structure. FTIR spectra suggest that the

incorporation of copper chloride reduces the peak height and also shifts the peak position

towards the lower wavelength. This indicates the interaction of copper chloride with amine and

imine sites of the polymer. From the TGA data they concluded that the composite of PANI-

copper chloride is thermally more stable than pure polyaniline. The conductivity of the

composite has a significant increase due to the incorporation of copper chloride. This increase in

conductivity is attributed to the presence of Cu which causes an increase of metallic island.

The humidity sensing ability of polyaniline composite with polyvinyl alcohol (PVA) was

investigated by Li et al. [29]. They used polystyrenesulfonic acid (PSSA) as a template to

prepare water soluble polyaniline by the oxidation of aniline in the presence of ammonium

persulfate as an oxidant. The resulting PSSA doped PANI was dissolved in water and PVA were

refluxed into the solution. The mixture was stirred overnight to ensure complete mixing. The

PANI-PSSA and PSSA doped PANI-PVA composites were characterized by UV/Vis, FTIR, and

TEM. The humidity sensing ability of PSSA doped PANI-PVA composite is higher than the pure

PANI and PANI-PSSA.

10

PANI-PVA conducting composites were investigated by Gangopadhyay et al. [30]. An

aqueous solution stabilized by PVA was used to synthesize HCl doped PANI in the presence of

ammonium persulfate (APS) as an oxidant. The composites were characterized by UV/Vis,

SEM, TEM, and TGA. The degree of polymerization of aniline in the presence of PVA is

reported to be decreasing due to the steric stabilization of PVA. They added that the dispersion

shows the conductivity of PANI and mechanical strength of PVA. The composite isolated from

the dispersion was subjected to TEM analysis which shows the presence of PANI spheres in the

network of PVA contrary to the rice-grain morphology or needle like morphology. From TGA

they concluded an appreciable increase in thermal stability of the composite.

J. Bhadra and Sarkar [10] synthesized a composite film of PANI-PVA to study its electrical

and optical properties. The SEM results show the presence of polyaniline grains on the PVA

matrix. The size of grains ranges from 0.3 to 1.2 µm. They reported that spherical and rod

shaped nanoparticles are formed at higher concentration of PVA. The amorphous nature of

composite was shown by XRD. They reported PANI-PVA cross linking from the FTIR spectra.

The decrease in conductivity is observed as PVA concentration increases in the composite.

1.2 Polyaniline

Polyaniline (PANI) formerly known as “aniline black” is deposited over the anode during the

electrolysis of aniline. Among the conducting polymers polyaniline (PANI) has got much more

attention due to its unique properties, like cost-effective monomers, high yield of reaction and

excellent stability [31]. PANI has got many industrial applications like resistance to corrosion in

paint industry, removal of mercury from water, light emitting diodes, surgical instruments, light-

weight batteries and solar cells [32-34].

11

1.2.1 Structure of Polyaniline

A linear octameric structure of PANI was proposed by Woodhead and Green [35, 36] for

the first time. According to them the aromatic aniline molecules are arranged head to tail at the

para position forming a linear chain. In PANI the flexible –NH- group is attached to the

phenylene group on either side. The presence of –NH- group is responsible for the physical and

chemical properties of PANI along with protonation and deprotonation process [37]. There are

three different oxidation states of PANI i.e. fully oxidized pernigraniline (PN), fully reduced

leucoemeraldine (LE), and half oxidized emeraldine base (EB) as shown in Figure 1.1. The

reason for the different oxidation states is due to the difference in the number of imine and amine

units in PANI. Among the three forms only the emeraldine salt (ES) is conductive which is

obtained by protonation of emeraldine base.

* N N N nN

Pernigraniline (Violet and insulator)

* NH NH NH NHn

Leucoemeraldine (Pale yellow and insulator)

12

* NH NH Nn

N

Emeraldine base (Blue and insulator)

* NH NH NHn

NH

Emeraldine salt (Green and conductive)

Figure 1.1 Various redox states of PANI.

1.2.2 Conductivity of polyaniline (PANI)

The existence of PANI in three different oxidation states (pernigraniline, leucoemeraldine

and emeraldine form) leads to the difference in physicochemical properties [13, 38, 39]. The

emeraldine base form of PANI is protonated to emeraldine salt form which has conductivity in

the range of semiconductors 100 S cm-1. The conductivity of emeraldine salt is more than that of

pure polymers (<10-9 S cm-1) while less than that of typical metal (>104 S cm-1). The emeraldine

salt can be converted back to emeraldine base by treatment with alkaline solution. The

interconversion of emeraldine base and emeraldine salt is shown in Figure 1.2 [39].

13

* NH NH Nn

N

+2nH A-2nH A

* NH NH NHn

NHAA

Figure 1.2. Interconversion of emeraldine base and emeraldine salt.

Depending on the doping of PANI the conductivity can be changed to a wide range (<10-12 to

~105 S cm-1) [40]. The physical and chemical properties of PANI change in response to the

various external inducements thereby providing the space to use the PANI material for various

applications, e.g., memory devices, catalysis and chemical sensors [41]. Other uses like electro

chromic devices, microelectronics, plastic development etc. are attributed to the combination of

electrical and material properties of PANI.

1.2.3 Mechanism of Conductivity

The variable electrical conductivity of polymers is attributed to doping. Extensive

research work has been conducted to investigate the transportation of charge in these polymers

but the phenomenon is still poorly understood [40]. The main reason for the transportation of

charge in conducting polymers is conjugation among the unsaturated carbon atoms. New type of

charge transfer phenomenon is observed in the conjugated polymers due to the existence of

localized electronic energy states less than the band gap arising due to changes in local bond

order [40]. During polymerization reactions topological defects are introduced into the

14

conducting polymers with non-degenerate ground states. The energy of the radical cation

generated by the removal of charge from the valence band lies in the band gap. when radical

cation is partly delocalized over some polymer fragments, it is called small polaron in solid state

physics terms. The polaron formation is responsible for two localized electronic states in the

band and structural deformation of the lattice. Brazovski and Kirova [42] proposed a model of

three optical transitions due to the formation of polaron.

The removal of the second electron from the system creates another polaron when an

electron is removed from another segment of the polymer or from the already existing polaron to

create a bipolaron. A bipolaron also causes structural deformation while the two charges act as a

single pair. The polaron and bipolaron become mobile in response to the external electric field

via the rearrangement of conjugation.

The increase in conductivity of PANI is attributed to the charged species generated

during the protonation of polymer [43]. Other mechanisms of conductivity of PANI include

temperature based one-dimensional variable range hopping or three-dimensional fluctuation-

induced tunneling models [44].

1.2.4 Synthesis of Polyaniline

Generally, the synthesis of polyaniline is carried out by two methods i.e. chemical

oxidative polymerization and electrochemical polymerization [12]. The chemical method of

polymerization involves the direct oxidation of aniline to polyaniline by the use of oxidizing

agents, like ammonium persulfate, hydrogen peroxide, potassium dichromate, potassium iodate

etc., in an acidic media at pH range between 0 and 2 [38]. However, neutral and basic media are

also reported for the chemical synthesis of polyaniline at a pH range of 9-10 [38]. High

15

molecular weight PANI can be obtained at low temperature ranging from -15 to 5 0C. The

chemical synthesis of PANI results in bulk quantity of product with ease of processibility.

However, the higher Ionic strength of the medium and the excess of the oxidant lead to the

formation of essentially inflexible material which is one of the disadvantages of chemical

method.

Other chemical methods include interfacial polymerization, emulsion polymerization, and

dispersion polymerization etc. A list of oxidants and polymerization routes are given in the

literature [38, 40].

The synthesis of PANI by electrochemical method involves the anodic oxidation of aniline on an

inert metallic electrode usually platinum using potentiostatic or galvanostatic mode. Other

electrode materials used are copper, lead, iron, and zinc [38]. In potentiostatic mode the potential

is fixed (ESCE= 0.7-1V) or cycled in a range of -0.2 to 0.7-1.2V. An inert atmosphere is provided

to carry out the anodic oxidation at ambient temperature. PANI synthesized by potential cycling

is more homogeneous [38]. The advantage of electrochemical method is the easy formation a

thin or thick coating for conceivable applications.

1.2.5 Mechanisms of polymerization

The nature and physicochemical properties of PANI, synthesized by a variety of methods,

differ up to a large extent. In order to identify the formation of intermediates and steps involved

in the synthesis of PANI various kinetic studies and mechanisms are proposed. The study of

these reaction mechanisms is of prime importance to correlate the properties of polymeric

material to the possible reaction routes [45]. In order to find out the mechanism for the synthesis

16

of PANI various chemical and electrochemical methods have been proposed by different

scientists which are reviewed in the literature [38].

The mechanism for PANI formation is supposed to be a self-catalyzing reaction which

obeys the law Kc= ∆i/n FA. Where n is the number of electron transferred, A is the electrode

area, F is faraday’s constant, and ∆i is the change in current. The value of Kc (Autocatalytic rate

constant) is ~0.47 s-1 when the thickness of PANI film is 140 nm [46]. The formation of a

radical cation is considered to be the first step in the mechanism for synthesis of PANI. The

radical cation is resonance stabilized as shown in Fig. 1.3.

NH2 NHH

. NHH

H.N

HH

.

H

NHH

.H

e-

Figure 1.3. Radical cation formation and its resonance stabilization.

According to Mohilner et al. [47] the oxidation of aniline in an acidic medium of sulfuric

acid ( pH 2-5) is a progression of fast electrochemical-chemical-electrochemical (ECE)

reactions, resulting in para-coupled chains. However, the radical coupling at ortho position is

responsible for the low yield of reaction due to un-exclusive para-coupling [38]. The first

reaction intermediate can react with a free monomer or undergo further oxidation. According to

Yang and Bard [48] in the early stages of PANI polymerization, the dimer of aniline (p-

aminodiphenylamin) is predominantly produced with another minor intermediate benzidine.(

Fig. 1.4)

17

NH

H

HNH

H

HHNH .

H

H

N

H

HNH

H

HH

N N

H

H

+

-2H

2 ..

H

Figure 1.4. Conversion of radical cation to para-aminodiphenylamine.

In the next step the para-aminodiphenylamine rapidly undergoes further polymerization resulting

in the formation of tetramer followed by octamer and ultimately results into emeraldine [47].

Since less positive potential is required for the electro-oxidation of oligomers as compared to

aniline monomer, therefore, the mechanism of aniline polymerization is proposed to be

autocatalytic which is observed in aqueous medium of considerable acidity [45].

1.2.6 Doping of PANI

The doping is achieved by the increase or decrease in the number of electrons associated

with the polymer due to the partial oxidation or reduction of π conjugated system of polymer

[40]. An appreciable change in electronic transport properties is observed when PANI is doped

with anions either chemically or electrochemically [49]. Among the oxidation states of PANI the

emeraldine form is susceptible to pH resulting in emeraldine base (EB) and emeraldine salt (ES).

The non-conducting EB can be converted into the conducting ES form without changing the total

number of electrons [50]. This can be achieved by the addition of mineral or organic acid to

protonate the –NH group of EB form of PANI. The addition of acid is called acid doping.

18

* N N N nN

* NH NH NHn

NHAA

+2nH A-2nH A

Figure 1.5. Acid doping of PANI.

The conductivity of acid doped PANI is more than eight orders of magnitude larger than the

undoped form [49]. During the process of protonation the accumulated positive charges on the

polymer backbone are neutralized by the counter (negatively charged) ions of the dopant.

Significant changes in the crystallinity, electronic structure, and solubility etc. are associated

with protonation [40]. The change in pH of dopant solution provides the way to control the

conductivity and degree of protonation by acid. The most commonly used dopants are mineral

acids like H2SO4 and HCl.

1.3 Characterization of PANI

The various physicochemical techniques used for the characterization of polyaniline

synthesized by chemical or electrochemical method are discussed below.

1.3.1 UV/Visible spectroscopy

UV/Visible spectroscopy is one of the most important characterization techniques for

PANI due to the various oxidation states of PANI with different colors. It is a useful tool to trace

the color changes associated with the sensitivity of PANI to pH changes. The qualitative

information about the degree of conjugation, level of doping and the existence of radical cation

19

in the polymer can be achieved by the electronic absorption spectra of PANI dissolved in

suitable solvent or electrochemically deposited over an electrode in the form of film. Clear

monitoring of the change from conductor to insulator with respect to change in pH of the

medium can be carried with ease. In order to understand the interconversion of different

oxidation states of PANI; in situ UV/Vis spectroscopy in combination with applied potential is

very useful. The change in electrical conductivity of different oxidation states can be correlated

with the change in absorbance values. The interaction between PANI and the molecules of

solvent used to dissolve PANI can also be studied by this method. The kinetics studies of aniline

polymerization can also be traced by the electronic absorption spectroscopy [45].

1.3.2 FTIR spectroscopy

The Fourier Transform Infrared (FTIR) spectroscopy is a non-destructive, faster, more

sensitive and widely used technique for the characterization of solids, liquids, gases, and film

samples in laboratory and industry. It is a powerful technique available to the chemists to find

out the structure of molecule present in the sample. The technique also finds its applications in

characterizing the intermediate products during the course of reactions. In case of PANI

characterization important information about the presence of bands for both amine and imine

groups can be gained which will determine the oxidation state of PANI products. The presence

of many functional groups on the polymer backbone can be deduced from the corresponding

bands in the FTIR spectrum. The doping and dedoping of PANI can also be studied from the

vibrational spectroscopy. The vibrational spectroscopic tool has many industrial applications in

characterizing samples related to biomedical research, foodstuff, polymerization products etc.

The vibrational spectroscopic technique is fast, has ease of calibration, more sensitivity,

excellent specificity and applicability in both quantitative and qualitative analysis.

20

1.3.3 X-ray diffraction (XRD)

X-ray diffraction is a non-destructive and unique technique to identify the crystallinity

and analyze the structural properties like crystal orientation, grain size, stress, defects and phase

composition by bombardment of the solid samples from different angles. The crystal lattice of

the sample diffract the X-ray from its various planes according to Bragg’s equation nλ=2dsinθ

where n is an integer, λ is the wavelength of X-ray, d is lattice planes distance and θ is the angle

of diffraction.

Figure 1.6. X-rays diffraction in a crystalline material.

A diffraction pattern emerges by the variation of the angle of incidence which is the

characteristic of the sample. The resultant X-ray pattern, along with peak positions, width,

intensities and shape, provides significant information about the possible structure of the

material. The X-ray diffraction of PANI will not show sharp peaks indicating the amorphous

nature of PANI which is the characteristics of polymers. However, at 2θ ranging from 20⁰-26⁰ a

21

diffused broad peak is displayed by the polymer samples. Insertion of metal will cause a change

in the XRD pattern of the polymer and corresponding change in the intensity, width and position

of the peak thereby causing an increase in the conductivity due to the increase in d-space [51].

1.3.4 Cyclic voltammetry

Cyclic voltammetry is a powerful, most widely used and efficient electrochemical

technique to acquire information about the inter conversion of various oxidation states of PANI.

Besides characterization, the technique also finds its applications in the synthesis of PANI.

Considerable information about the kinetics and thermodynamics of oxidation-reduction

reactions can readily be deduced from the cyclic voltammetry. The electrochemical responses of

various oxidations states of PANI results in the appearance of peaks at various positions in the

cyclic voltamogram (plot of current verses potential). The interconversion of any two oxidation

states of PANI along with the injection of charge can be studied from the peaks in the cyclic

voltamogram. Cyclic voltammetry also provides important information about the effect of

supporting electrolyte on the morphology and conductivity of PANI during the process of

polymerization.

1.3.5 Scanning electron microscopy (SEM)

The physicochemical properties of powder PANI, synthesized chemically, or PANI films,

synthesized electrochemically, are highly influenced by the morphology of polymer [38]. The

morphology of PANI is generally investigated by scanning electron microscopy (SEM). The

micro and nano structures of PANI can be studied at a high magnification. Various

physicochemical properties like crystallinity, mechanical strength, electrical conductivity etc. can

be related to the surface morphology obtained from SEM images.

22

1.3.6 Elemental analysis

Elemental analysis is one of the basic characterization techniques used in synthetic

chemistry to find out the composition of sample material. The stoichiometry of sample material

can be calculated from the percent weight of carbon, hydrogen, nitrogen and sulfur which are

provided by the elemental analysis. Moreover, the ratio of carbon to hydrogen and carbon to

nitrogen can also be calculated from the elemental analysis. The degree of doping can also be

calculated from the elemental analysis for example, when transition metal salts of Fe (III), and

Cu (II) are used as dopant in PANI chains, the imine site co-ordinates with the metal cation

resulting in the 85% and 50% doping of PANI by iron and copper ion respectively [52].

Important information about deducing the structure and molecular weight of the sample material

are provided by elemental analysis. In case of PANI the C/N ratio and H/C ratio is useful in the

determination of the oxidation state of PANI.

1.4 Solubility of PANI

The solubility of polyaniline is of high interest regarding its scientific and commercial

applications. Scientifically the elucidation of molecular structure and configuration from the

molecular weight obtained by the analytical data provided by solubility of PANI is of prime

importance. Commercially many technological devices can be designed by the soluble PANI [3].

The conducting polymers are mostly insoluble in their doped state [53]. The poor

processibility of conducting emeraldine salt form of PANI is attributed to its non solubility in

common organic solvents [54]. According to Heeger [31] the discovery of PANI paved the way

to overcome the problem of processibility of conducting polymers. However, the poor solubility

of high molecular weight PANI is a barrier in making useful devices and objects. The instability

23

of PANI at melt process temperature has blocked the way of processing it like conventional

thermoplastics polymers [55]. The fundamental thermodynamic properties like unfavorable

entropy of dissolution, unmoldability and high lattice energy of PANI has high influence on the

solubility of PANI [56]. Another reason for the poor solubility of PANI is the non availability of

such solvents which could simultaneously dissolve both the hydrophobic and hydrophilic part of

the polymer. In order to improve upon the solubility and processibility of PANI many attempts

has been made by scientists from all over the world [57]. The use of substituted aniline as

monomer, copolymerization of aniline, blending of PANI with other polymers, doping with

anionic surfactants and formation of PANI composites are being extensively studied. A brief

discussion of the above mentioned methodologies is given below.

1.5 Polymerization of substituted aniline

The use of substituted aniline for polymerization to improve upon the solubility of PANI

is one of the most recently studied methodologies. The substituent like alkoxy [58], alkyle [59],

phosphoric acid [60], sulfonic acid [61] groups with a solubilizing effect are chosen for the

purpose of increasing solubility of resulting polymer. In addition to increase the solubility of

PANI the thermal stability of acid doped PANI is also increased. The substituted aniline can also

be polymerized chemically [62] or electrochemically [63] just in the same way as their parent

monomer. The major problem with the polymerization of substituted aniline is the decrease in

conductivity of resulting polymer [64].

24

1.5.1 Copolymerization of aniline

In order to bring the diverse physicochemical properties of different polymers into a

single polymer structure the copolymerization technique is applied. As discussed before, that the

conductivity is greatly reduced by the polymerization of substituted aniline at the cost of

solubility but in case of copolymerization the resulting polymeric system has the conductivity

just like PANI and solubility like the polymers obtained by the polymerization of substituted

aniline [65-67].

1.5.2 PANI blends

A blend is a mixture of two or more physically mixed polymers having different chemical

composition. Several types of PANI conductive blends with an increase in processibility are

reported in literature [68, 69]. The idea of PANI blends was introduce to make it melt

processable by increasing stiffness and flexibility of PANI. The mechanical strength of the blend

decreases to a high extent as a result of phase separation between the two components [70]. High

flexibility for the material having less than 16 % PANI composition by weight has been reported

in literature [69]. The PANI salt blended with poly(vinyl chloride) [71], poly(vinyl alcohol) [72],

poly(styrene) [73] and poly(amides) [74] are being extensively studied.

1.5.3 PANI doped with surfactants

The synthesis of high molecular weight PANI is carried out by the chemical

polymerization of aniline in a micelles system which not only increases the yield of reaction but

also leads to accelerated polymerization [75]. Similarly, the presence of sodium dodecyl sulfate

(SDS) accelerates the electro-polymerization of aniline [76]. Colloidal PANI dispersion

25

synthesis is also reported in the presence of SDS as surfactant [75, 77, 78]. The dispersion of

HCl doped PANI synthesized in the presence of SDS micelle medium is reported to be stable up

to a pH =8 [75]. SDS was used as a surfactant by Hassan et al. [79] for the polymerization of

aniline and reported that the polymer size is greatly affected by both the concentration of

monomer and micelle size. In the synthesis of polymer in the presence of micelle the

polymerization reaction takes place at the interface of micelle-water system. In such system

dynamic equilibrium exist between the surfactant monomers and micelle in the solution. The

intermediate hydrophobic products obtained from the polymerization are incorporated into the

micelles because of their poor solubility in water. The SDS molecule are incorporated and

adsorbed in the polymer particles thereby stabilizing them [77].

1.5.4 Composites of PANI

In recent years researchers have shown a great deal of interest in the organic- inorganic

composites due to their potential applications in various technological processes. Among these,

PANI is of much importance due to its versatile conducting properties. The conductivity of

PANI can be tuned by doping with suitable dopants. The composites of PANI with noble metals

can be used in optical and electrical appliances and also for catalytic purposes [80]. The

reduction of silver nitrate by using emeraldine base (EB) form of PANI was carried out by

stejskal et al. [81] to synthesize PANI-silver nanocomposites. The resulting PANI-silver

nanocomposites show an increase in conductivity. PANI-gold nanocomposites were synthesized

by Gupta et al. [82] using chemical oxidative method and studied the optical and electrical

transport properties. In another study Gupta and his coworkers [5] synthesized the PANI-silver

nanocomposites and reported their electrical transport and optical properties.

26

1.6 Aims and objectives of the work

The aims of the present study are twofold: (a) To study the effect of the use of copper(II) as a

milder oxidizing agent than those normally used (ammonium persulfate, benzoylperoxide,

hydrogen peroxide, etc.) on the aniline polymerization reaction and its potential PANI product.

(b) To determine the nature of any copper incorporated in the reaction product. The latter is

particularly important in relation to the proposed use of such reactions to produce

polyaniline/metal composite materials, which are the subject of a recent review [83], but it is

evident from the literature cited above that the chemical state of the copper that has been

proposed to be incorporated in the product is quite variable [83-86]. Indeed, the formation of

PANI by the oxidation of aniline by copper(II) compounds has been called into question in

studies of reactions of aniline with CuSO4, CuCl2 and CuBr2, where 2:1 coordination adducts of

aniline with these copper(II) compounds precipitated rather than the expected PANI product

[87]. In the present work we extend the study of the CuCl2/aniline system to explore the effect of

using higher CuCl2 concentrations; previous studies have shown that the oxidation potential of

CuCl2 increases with increasing concentration [88]. A previous study [86] has proposed a

catalytic (rather than an oxidative) role for copper(II) in aniline oxidation reactions in the

presence of copper(II). The possibility that PANI might be formed catalytically by aerial

oxidation of aniline in the presence of CuCl2 has been excluded in the present study by carrying

out the reaction in the absence of air. It was found that polyaniline emeraldine base (EB-PANI)

doped with [CuCl3]- forms under these conditions. CuCl2 is a weaker oxidant than, e.g. AgNO3,

and this study further supports the view that weak oxidizing agents can be used for aniline

polymerization reaction. The reaction yield is low, but can be increased by increasing the CuCl2

concentration. The present study also focuses on the synthesis and characterization of PANI and

to make its composites with copper and polyvinylalcohol (PVA) and to investigate into the

conductivity, crystallinity, redox properties and stability of resulting composites.

***********************

28

2. EXPERIMENTAL

PART I

2.0 Synthesis and Characterization of Polyaniline by using CuCl2 as Oxidizingagent

2.1 Material

Aniline monomer (99.5%) was purchased from Sigma Aldrich and distilled twice before

use. p-toluene sulfonic acid (p-TSA) (synthesis grade) was purchased from Scharlau and used as

received. Anhydrous copper chloride (97%) from Sigma Aldrich was used as received.

2.2 Procedure

A 10 mL solution of (0.2 M aniline and 0.2 M p-TSA) was prepared in milli-Q water.

The pH of the solution was 4.70. This solution was placed at 5±1 0C for 10-15 minutes. 10 mL of

3 M pre-cooled copper(II) chloride solution was added dropwise to 10 mL of the aniline-p-TSA

solution under nitrogen atmosphere. The reaction mixture was left undisturbed for 24h at room

temperature under nitrogen atmosphere. The reaction mixture turned greenish black and had a

final pH of 2. The precipitate was filtered and washed several times with milli-Q water followed

by acetone. The product was dried for 24 h in a vacuum oven at room temperature and labeled as

B-PANI. Similar reactions with oxidant : monomer ratios ‘R’ from 1 to 15 were investigated by

varying the CuCl2 concentration. The B-PANI was washed with 1M HCl to remove basic

impurities and the sample was labeled as H-PANI. When the B-PANI was treated with 35%

hydrazine it was labeled as PANI (Scheme 1).

29

Scheme 1.Treatment of the B-PANI sample with various chemicals to get the products.

2.3 Dedoping of B-PANI and H-PANI

The B-PANI and H-PANI samples were dedoped with 10% NH4OH solution according

to the procedure described by Bian and Yu [89]. The dedoped PANI samples were labeled as

DB-PANI and DH-PANI (Scheme 1).

2.4 Reduction of PANI, DB-PANI and DH-PANI

The PANI, DB-PANI and DH-PANI samples were reduced by the addition of 35%

aqueous hydrazine [90] and labeled as R-PANI, RB-PANI and RH-PANI, respectively (Scheme

1).

2.5 Characterization

The yield of product was calculated for reactions with various oxidant to monomer ratios

ranging from 1 to 15. The initial and final pH of the reaction mixture was measured for these

oxidant to monomer ratios. The weight loss following the washing of the products was also

calculated.

2.5.1 FTIR Spectroscopy

A Perkin Elmer series Spectrum 400 FTIR spectrometer was used to record FTIR spectra.

The spectral region from 4000 to 400 cm-1 was selected with a resolution of 4 cm-1 for all

30

samples. The number of scans for each sample was 10 and the spectra were collected in

attenuated total reflection (ATR) mode. For the data analysis the standard software (Sigma plot

11) was used.

2.5.2 UV/Vis Spectroscopy

The UV-Vis spectra were recorded on solutions in N-methyl pyrrolidone (NMP) as

solvent using a Shimadzu UV/Vis 1700 spectrophotometer. The spectral region from 900 to 200

nm was selected with a sampling interval of 0.5 nm.

2.5.3 Elemental Analysis

Elemental analysis was carried out by the Cambell Microanalytical Laboratory at the

University of Otago, Dunedin, New Zealand.

2.5.4 X-ray Photoelectron Spectroscopy (XPS)

XPS data were collected using a Kratos Axis Ultra DLD equipped with a hemispherical

electron energy analyzer and an analysis chamber of base pressure ~1×10-9 torr. Samples were

excited using monochromatic Al Kα X-rays (1486.69eV), with the X-ray source operating at 100

W. Samples were mounted on carbon adhesive tape for analysis. A charge neutralization system

was used to alleviate sample charge build up during X-ray irradiation. Survey scans were

collected at a pass energy of 80 eV over the binding energy range 1200-0 eV, while core level

scans were collected with a pass energy of 20 eV. The spectra were calibrated against the C 1s

signal at 285 eV from adventitious hydrocarbons. Elements present in the samples were

quantified based on C 1s, N 1s, Cu 2p, Cl 2p, Si 2p and S 2p peak areas and relevant sensitivity

factors.

2.5.5 Near Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy

N K-edge NEXAFS data was recorded on the soft X-ray spectroscopy beam line of the

Australian Synchrotron. The NEXAFS data was taken in both partial electron yield (PEY) mode.

The PEY spectra were normalized to a photo-diode current measured simultaneously to cancel

any contributions originating from impurities present in the beam line which may contribute to

31

changes in the photon intensity. The measurements were carried out in high resolution (HR)

mode by increasing the photon energies in steps of 0.05 or 0.1 eV.

2.5.6 Solid-State NMR

All solid-state NMR experiments were carried out on dry powdered samples using a

Bruker AVANCE 300 spectrometer operating at 300.13 MHz proton frequency. Basic spectra

were obtained by using the standard CP MAS (Cross-Polarization Magic Angle Spinning)

technique. The experiments were carried out using a 7 mm Bruker spinning probe with zirconia

rotors. The magic angle was adjusted by maximizing the side bands of the 79Br signal of a KBr

sample. The proton 90o pulse duration was 4.2 μs and the frequency of the continuous wave

decoupling field was 62.5 kHz. The contact time was 1.5 ms. The spectral width was 40 kHz.

The 13C chemical shift scale is referenced to tetramethylsilane (TMS). The samples were rotated

at 7000 1 Hz.

2.5.7 SEM Analysis

The SEM analysis was performed in Centralized Resource Laboratories (CRL)

University of Peshawar, Pakistan by using scannining electron microscope Model JSM-5910

JEOL Japan.

PART II

2.6 Synthesis and Characterization of Leucoemeraldine

2.6.1 Materials

Aniline monomer (99.5%) was purchased from Sigma Aldrich and distilled twice before

use. para-toluene sulfonic acid (Synthesis grade) was purchased from Scharlau and used as

received. Anhydrous copper chloride (97%) from Sigma Aldrich was used as received.

2.6.2 Procedure

A 10 mL solution of (0.2 M p-TSA and 0.2 M aniline) was prepared in deionized water.

The pH of the solution was 4.80. 10 mL of this solution was placed at 5±1 0C for 15-20 minutes.

10 mL (0.01 M copper chloride) precooled solution was added to the aniline-p-TSA solution.

32

The reaction mixture was stirrered at room temperature under the nitrogen atmosphere, for 24 h.

The final pH of reaction mixture was found to be 3.7. The precipitate was centrifuged and

washed with deionized water followed by acetone to remove unreacted material. The product

obtained was dried for 24h at room temperature in a vacuum oven and labeled as L-PANI. The

oxidant: monomer ratios 0.05, 0.25, 0.50, 0.75, 1 and 1.25 were investigated by changing the

concentration of CuCl2.

2.6.3 Characterization

The amount of product was calculated for various oxidant to monomer ratios ranging

from 0.05 to 1.25. The initial and final pH of various oxidant to monomer ratios in the reaction

mixture was noted.

2.6.3.1 FTIR Spectroscopy

FTIR spectra were recorded by using Perkin Elmer spectrophotometer series 400 FTIR.

The spectra were recorded in the spectral region ranging from 4000 to 400 cm-1 with a resolution

of 4 cm-1. The spectra were collected in attenuated total reflection (ATR) mode with 10 numbers

of scans for all samples. The standard software (Sigma plot 11) was used for the data analysis.

2.6.3.2 UV/Vis Spectroscopy

A Shimadzu UV/Vis 1700 spectrophotometer was used to record the UV/Vis spectra. The

sampling interval was 0.5 nm and the spectra were recorded in spectral region ranging from 800

to 200 nm.

2.6.3.3 Elemental Analysis

Elemental analysis was performed by using Elementar CHNS Analyzer Germany at

Pakistan Council of Scientific and Industrial Research (PCSIR) Laboratory Peshawar, Pakistan.

33

PART III

2.7 Synthesis and Characterization of Polyaniline Doped with Cu II Chloride

by Inverse Emulsion Polymerization

2.7.1 Materials

Aniline monomer reagent grade was purchased from Acros organics and distilled twice

before use. Toluene (BDH), 2-propanol (Merck), benzoyl peroxide (Merck) and DBSA (Acros)

were used as received.

2.7.2 Procedure

The material was synthesized according to the procedure mentioned in literature [13]. In

a typical experiment 50 mL of toluene was taken in a 100 mL round bottom flask. 0.40 g

Benzoyl peroxide was added to it under mechanical stirring. 10 mL of 2-propanol was added to

the above solution. To the above mixture 1.5 mL DBSA, 0.2 mL aniline and 10 mL (0.6M

CuCl2) solution in deionized water was added to form a white milky emulsion. A greenish brown

color appears after 7 hours. The reaction was allowed to proceed for 24h. In the end the mixture

was transferred into a separating funnel for the separation of organic layer from the aqueous

layer. The organic layer containing polyaniline was extensively washed with acetone and the

product obtained was transferred into a petri dish and dried in oven for 24h at 40 0C. The

polymer was broken into flakes by the addition of small amount of acetone. The polymer was

separated from the petri dish and labeled as PANI-Cu. Several different concentrations of CuCl2

were investigated. For PANI sample preparation only deionized water was added to produce the

milky emulsion.


The amount of product was calculated for various addition of CuCl2 solution ranging

from 0.2 to 0.7M.

2.7.3.1 Conductivity Measurements

A four point probe Jandel Model RM2 instrument was used to carry out the conductivity

measurements of the PANI-Cu composites. The powder samples were compressed to form a

34

solid pellet and four electrical contacts were made with the solid pellet to measure the

conductivity.


A Shimadzu UV/Vis 1700 spectrophotometer was used to record the UV/Vis spectra. The

spectra were recorded with a sampling interval of 0.5 nm in the spectral region from 900 to 200

nm.


FTIR spectra were recorded in a region ranging from 400 to 4000 cm-1 by using IR

Prestige-21 FTIR Spectrophotometer Shimadzu Japan. The number of scans for each sample was

10.

2.7.3.4 Thermo Gravimetric Analysis (TGA)

The TGA was performed on solid samples at a temperature range from 0 to 600 0C by

using Diamond TG/DTA Perkin Elmer USA in the Centralized Resource Laboratories University

of Peshawar Pakistan.

2.7.3.5 X-ray Diffraction (XRD) Analysis

The XRD analysis of solid samples was carried out by using Siemens diffractometer D

5000 at the Polymer Electronic Research Centre University of Auckland New Zealand.

2.7.3.6 Scanning Electron Microscopy

The SEM was carried out in Centralized Resource Laboratories University of Peshawar

Pakistan by using scannining electron microscope Model JSM-5910 Jeol Japan.

2.7.3.7 Cyclic Voltammetry

Cyclic voltammetry (CV) was carried out in National Centre of Excellence in Physical

Chemistry, University of Peshawar, Pakistan by using ALS/DY 2323 Biopotentiostate. A gold

coiled wire was used as counter electrode while gold foil (9.1×9.6 mm in size) and 0.27 mm

thick was used as working electrode. The calomel electrode was used as reference. On the gold

foil electrode a thin film of the polymer was deposited and the CVs were recorded with a scan

rate of 50 mV S-1 in 0.5M H2SO4 solution as supporting electrolyte.

35

PART IV

2.8 Synthesis and Characterization of Polyaniline Doped with

Polyvinylalcohol by Inverse Emulsion Polymerization

2.8.1 Materials

Reagent grade aniline monomer was purchased from Acros Organics and distilled twice

before use. DBSA (Acros), 2-propanol (Merck), benzoyl peroxide (Merck), and toluene (BDH)

were used as received.

2.8.2 Procedure

The samples were synthesized according to the procedure mentioned in literature [13]. In

a typical experiment 50 mL of toluene was taken in a 100 mL round bottom flask. 0.40 g of

benzoyl peroxide was added to it under mechanical stirring. To the above solution 10 mL of 2-

propanol was added. 1.5 mL DBSA, 0.2 mL aniline and 10 mL (1% PVA) solution, in deionized

water, was added to the above mixture to form a white milky emulsion. The reaction mixture

turns greenish brown after 7h and was allowed to proceed for 24h. The aqueous layer was

separated from the organic layer in a separating funnel. Extensive washing of the organic layer

with acetone was carried out until the unreacted material is removed and the product obtained

was transferred into a petri dish and dried in oven for 24h at 40 0C. The polymer was broken into

flakes by the addition of small amount of acetone. The polymer was separated from the petri dish

and labeled as PANI/PVA. Several different concentrations of PVA were investigated.


The amount of product was calculated for various addition of CuCl2 solution ranging

from 0.2 to 0.7M.

36

2.8.3.1 Conductivity Measurements

The conductivity measurements of the PANI/PVA composites were carried out by using

four point probe Jandel Model RM2. Four electrical contacts were made with the solid pellet

compressed under high pressure of 800 bar.


To record the UV/Vis spectra a Shimadzu UV/Vis 1700 Spectrophotometer was used.

The spectral region from 900 to 200 nm was selected and the spectra were recorded with a

sampling interval of 0.5 nm.


FTIR spectra were recorded by using IR prestige-21 FTIR Spectrophotometer Shimadzu

Japan in a region ranging from 400 to 4000 cm-1. The spectra were collected with 10 numbers of

scans for each sample.

2.8.3.4 Thermogravimetric Analysis (TGA)

The TGA was performed on solid samples at a temperature range from 30 to 600 0C by

using Diamond TG/DTA Perkin Elmer USA in the Centralized Resource Laboratories University

of Peshawar Pakistan.

2.8.3.5 X-ray Diffraction (XRD) Measurements

The XRD of solid samples was carried out by using Siemens diffractometer D 5000 at the

Polymer Electronic Research Centre University of Auckland New Zealand.

2.8.3.6 Scanning Electron Microscopy (SEM)

The SEM was carried out in Centralized Resource Laboratories University of Peshawar

Pakistan by using scannining electron microscope Model JSM-5910 JEOL Japan.

37


Cyclic voltammetry (CV) was carried out by using ALS/DY 2323 Biopotentiostate in

National Centre of Excellence in Physical Chemistry, University of Peshawar, Pakistan. Gold

foil was used as working electrode and gold coiled wire as counter electrode. The calomel

electrode was used as reference. A thin film of the polymer was deposited on the gold electrode

and the CVs were recorded in 0.5M H2SO4 solution as supporting electrolyte. The scan rate was

50 mV S-1.

PART V

2.9 Synthesis and Characterization of Polyaniline Co-doped withPolyvinylalcohol and Cu by Inverse Emulsion Polymerization

2.9.1 Materials

The monomer aniline (reagent grade) was purchased from Acros Organics and distilled

twice before use. Dodecylbenzene sulfonic acid (DBSA) from Acros Organics, 2-propanol and

benzoyl peroxide (BPO) from Merck and toluene from BDH were used as received.

2.9.2 Procedure

The synthesis was carried out according to the procedure mentioned in [13]. In a typical

experiment 0.40 g of BPO was added to 50 mL of toluene, under mechanical stirring in a 100 mL

round bottom flask. 2-propanol (10 mL) was added to the above solution. 1.5 mL of DBSA, 0.2

mL of aniline and 10 mL (0.6M CuCl2) solution in deionized water was added to the above

mixture to form a white milky emulsion. 10 mL of 1% PVA solution was also added to the above

mixture. The reaction was allowed to proceed for 24h. After 24h the aqueous and organic layers

were separated in a separating funnel. The organic layer was extensively washed with acetone to

remove the unreacted material. The product obtained was transferred into a petri dish and dried

in oven for 24h at 40 0C. The polymer was broken in to flakes by the addition of small amount of

acetone. The polymer was separated from the petri dish and labeled as PANI-Cu-PVA. Several

different concentrations of CuCl2 and PVA solutions were investigated. The same procedure was

repeated to synthesize PANI, PANI-Cu, and PANI-PVA. The PANI samples were synthesized

38

without the addition of CuCl2 and PVA. The PANI-Cu was synthesized without the addition of

PVA solution and PANI-PVA was synthesized without the addition of CuCl2 solution.


The synthesized material was characterized by using the following techniques.

2.9.3.1 Conductivity and Mass Measurement

The conductivity measurements of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA

were carried out by using four point probes Jandel Model RM2. Four electrical contacts were

made with the solid pellet compressed under high pressure of 800 bar.


UV/Vis spectra were recorded by using Shimadzu UV/Vis 1700 Spectrophotometer. The

selected spectral region was from 900 to 200 nm, with a sampling interval of 0.5 nm.

2.9.3.3 FTIR spectroscopy

IR Prestige-21 FTIR Spectrophotometer Shimadzu Japan was used to record the FTIR

spectra. The numbers of scans for each sample was 10 and the spectral region rang was 400 to

4000 cm-1.

2.9.3.4 Thermogravimetric Analysis

The TGA was performed by using Diamond TG/DTA Perkin Elmer USA, on solidsamples at a temperature range from 30 to 600 0C at the Centralized Resource Laboratories,University of Peshawar, Pakistan.

2.9.3.5 X-ray Diffraction Measurement

Siemens diffractometer D 5000 at the Polymer Electronic Research Centre, University of

Auckland, New Zealand was used to carry out the XRD of solid samples.

2.9.3.6 Scanning Electron Microscopy

The SEM images were taken in Centralized Resource Laboratories, University of

Peshawar, Pakistan by using scannining electron microscope Model JSM-5910 JEOL Japan.

39


Cyclic voltammetry (CV) was carried out by using ALS/DY 2323 Biopotentiostate in

National Centre of Excellence in Physical Chemistry, University of Peshawar, Pakistan. Gold

foil was used as working electrode and gold coiled wire as counter electrode. The calomel

electrode was used as reference. A thin film of the polymer was deposited on the gold electrode

and the CVs were recorded in 0.5M H2SO4 solution as supporting electrolyte. The scan rate was

50 mV S-1.

***********************

40

3. RESULTS AND DISCUSSION

3.1 pH Measurement and Mass Yield Calculations

The measurement of pH and mass yield are important tools to observe the course of

aniline polymerization. Normally a decrease in pH is observed due to the release of protons

during aniline polymerization and the mass yield is associated with change in pH as discussed in

previous literature [91].

Table 3.1. Initial and Final Solution pH and Mass Yields for Reactions with Various Oxidant to

Monomer Ratios R

R Initial pH Final pH Mass yield (g)

1 4.70 4.22 0.017

2 4.85 3.72 0.028

3 4.82 3.60 0.034

4 4.72 3.17 0.026

5 4.78 2.67 0.037

6 4.70 2.69 0.034

7 4.78 2.62 0.038

8 4.82 2.36 0.050

9 4.78 2.29 0.050

10 4.81 2.18 0.052

11 4.80 2.27 0.054

12 4.75 2.13 0.054

41

13 4.72 2.08 0.057

14 4.75 1.87 0.067

15 4.73 1.70 0.076

Table3.1 shows the initial pH, final pH, and mass yields for aniline polymerizations with

various oxidant to monomer ratios R. From Table 3.1 it is clear that the final pH decreases and

the reaction yield increases with an increase in the oxidant to monomer ratio. This increase in the

yield is most likely due to an increase in the oxidation potential of CuCl2 with an increase in its

molar concentration [88]. The generally low yield of reaction is attributed to the co-formation of

a copper(II) chloride-aniline complex [87]. In the present study this complex was removed by

washing with water and acetone.

Table 3.2. Weight (%) Loss of B-PANI after washing with HCl, NH4OH and N2H4 and

corresponding Mass Yield of H-PANI, DB-PANI and PANIa

% Loss with HCl/

Mass yield H-PANI

% Loss with NH4OH/

Mass yield of DB-PANI

% Loss with N2H4/

Mass yield of PANI

81±5

0.0157a

67±5

0.0246

54±5

0.0352

aThe mass yields of DH-PANI, RB-PANI, R-PANI and RH-PANI (Scheme 1) were 0,0121, 0.0157,

0.0243 and 0.0093 g respectively.

Table 3.2 shows that the % weight lost during washing with HCl, NH3 and N2H4 solutions

is very high, which is an indication of the presence of a large amount of Cu2(OH)3Cl,[87] which

is responsible for the nonconductive behavior of the B-PANI products. The mass yields (Table 2)

are a small percentage (ca. 10% or less) of the mass of aniline used in the reaction (0.204 g),

indicating that the percentage yields based on aniline are quite low. The H-PANI product with R

= 15 shows a conductivity of 2.3×10-1S cm-1.

42

3.2 FTIR Spectroscopy

All the data in the subsequent discussion are for the R=15 case.

Figure 3.1. FTIR spectrum of the initial product (R = 15) before washing.

The FTIR spectrum of the initial product obtained from the reaction in which the oxidant

(CuCl2) to monomer (aniline) mole ratio R = 15 before washing is shown in Fig. 3.1.

Comparison of this spectrum with literature data showed close similarities between this product

and that obtained by Le Cocq et al. [87]. The presence of two narrow bands around 1601 and

1567cm-1 show that the product is a 1:2 complex of copper(II) chloride with aniline which is

similar to that reported earlier [87]. Another similarity with the said report is the presence of two

bands at 3443 and 3368 cm-1 indicating the presence of an inorganic basic copper(II) chloride

product similar to Cu2(OH)3Cl that was observed in a previously reported study [87]. Since the

reaction is carried out in water, a possible mechanism for the formation of Cu2(OH)3Cl is as

follows:

C6H5NH2 + H2O→ C6H5NH3+ + OH− (1)

2CuCl2 + 3OH−→Cu2(OH)3Cl + 3Cl− (2)

43

When the initial product was extensively washed with milli-Q water followed by washing with

acetone, the peaks of the CuCl2/aniline complex disappeared and those of the basic copper(II)

chloride were shifted to 3512 and 3430 cm-1, close to the positions for Cu2(OH)3Cl, [87] as

shown by the spectrum of the product B-PANI in Fig. 3.2A(a).

cm-1

1000200030004000

%T

30

40

50

60

70

80

90

100

110

a

b

c

3.2A

cm-1

1000200030004000

%T

50

60

70

80

90

100

110

a

b

3.2C

cm-1

1000200030004000%

T

20

40

60

80

100

120

a

b

3.2B

cm-1

1000200030004000

%T

70

80

90

100

110

120

a

b

3.2D

Figure 3.2. FTIR spectra of A(a) B-PANI, (b) H-PANI(c) PANI, B(a) DB-PANI and (b) RB-

PANI, C(a) PANI and (b) R-PANI, D(a) DH-PANI and (b) RH-PANI.

In Fig. 3.2A(a) B-PANI the peaks at 1580 and 1488 cm-1 are assigned to the quinoid and

benzenoid unit of polyaniline. The peaks at 1315 and 1243 are attributed to the C-N and C=N

44

stretching modes. The bands at 1142 and 819 cm-1are assigned to the C-H in-plane and out-of-

plane bending modes [17]. The two intense peaks at 3512 and 3430 cm-1 are assigned to the O-H

stretching modes of Cu2(OH)3Cl [87].

Washing the product B-PANI with 1M HCl produces H-PANI whose FTIR spectrum is

shown in Fig. 3.2A(b). From this it is evident that the peaks for Cu2(OH)3Cl have disappeared.

This is attributed to dissolution of the Cu2(OH)3Cl in the HCl to form soluble CuCl2. Treatment

of B-PANI with 35% hydrazine produces PANI, whose FTIR spectrum is shown in Fig. 3.2A(c).

This shows that the peaks for Cu2(OH)3Cl can also be removed by reduction with hydrazine.

This is attributed to reduction of the copper(II) compound Cu2(OH)3Cl to copper(I) chloride,

with consequent removal of the OH stretching bands from the spectrum. The remaining peaks in

H-PANI and PANI are in good agreement with those of the emeraldine base (EB) form of

polyaniline [90].

The FTIR spectra of the products obtained by dedoping of B-PANI with 10% aqueous

ammonia (DB-PANI) followed by reduction with 35% hydrazine (RB-PANI) are shown in Fig.

3.2B (a), (b) respectively. In the spectrum of DB-PANI (Fig. 3.2B (a)) the peaks at around 1583

and 1481 cm-1 are assigned to the quinoid and benzenoid group of PANI. In RB-PANI

(Fig.3.2B(b)) the intensity of the peak at 1583 cm-1 is reduced and that at 1481 cm-1 is increased

indicating the reduction of sample by hydrazine [90].

In Fig. 3.2C the spectrum of PANI (Fig. 3.2C(a)) is compared with that of the product R-

PANI, obtained when the sample B-PANI is treated with 35% hydrazine and then further

reduced with 50% hydrazine for 24h (Fig. 3.2C(b)). A clear decrease in the intensity of the peak

at around 1588 cm-1 for the quinoid unit of PANI is observed as compared to the benzenoid unit

of PANI at around 1492 cm-1. This is attributed to the reduction of the EB form to

leucoemeraldine base (LB). The presence of a weaker peak at 1588 cm-1 indicates that a small

amount of quinoid units are still present in the polymer chain [90].

The FTIR spectra of the products obtained by dedoping of H-PANI with 10% aqueous

ammonia (DH-PANI) followed by reduction with 50% hydrazine for 24 hours (RH-PANI) are

shown in Fig. 3.2D(a), (b) respectively. A significant decrease in the intensity of the peak at

around 1594 cm-1 for the quinoid unit of PANI is shown by the spectra RH-PANI confirming the

reduction of sample [90]. This is attributed to the conversion of quinoid units into the bezenoid

45

units by the addition of hydrogen from hydrazine and evolution of nitrogen gas from the reaction

mixture.

3.3 UV/Vis Spectroscopy

Generally there is a strong absorption in the regions of 320-330 nm and 600-660 nm in

the UV/Vis spectra of the emeraldine base (EB) form of PANI. The band at 320-330 nm is

assigned to a π−π* transition of the bezenoid unit while the band at 600-660 nm is attributed to

the excitation of the quinoid segment [92].

The UV/Vis spectra of B-PANI, H-PANI and PANI are shown in Fig. 3.3A (a), (b) and

(c) respectively. The peaks at around 320-330 show the π−π* transition in the benzenoid segment

[93], while the peak for the quinoid segment of polyaniline in B-PANI and H-PANI is shifted

towards lower wavelength. FTIR (Fig. 3.2 A(a), B-PANI) and XPS (Fig.3.4 (a), H-PANI) data

indicate that copper(II) is still present in these products, and this wave number shift is possibly

due to a contribution from copper(II) chromophores.

46

a

b

c

nm

300 400 500 600 700 800 900

Abso

rban

ce

0.0

0.5

1.0

1.5

2.0

2.5

B-PANIH-PANIPANI

a

b

c

33.3A

nm

300 400 500 600 700 800 900

Abs

orba

nce

0.0

0.2

0.4

0.6

0.8

1.0

PANIR-PANI

a

b

3.3C

300 400 500 600 700 800 900

Abso

rban

ce

0.0

0.5

1.0

1.5

2.0

RB-PANIDB-PANI

nm

a

b

3.3B

nm

300 400 500 600 700 800 900

Abs

orba

nce

0.0

0.5

1.0

1.5

2.0

DH-PANIRH-PANI

H-PANIa

b

c

3.3D

Figure 3.3. UV/Vis spectra of A(a) B-PANI, (b) H-PANI, (c) PANI, B(a) DB-PANI (b) RB-

PANI, C(a) PANI, (b) R-PANI, D(a) H-PANI, (b) DH-PANI and (c) RH-PANI.

The UV/Vis spectra of DB-PANI and RB-PANI are shown in Fig.3.3B (a) and (b). In

Fig. 3.3B(a) the UV/Vis spectrum of DB-PANI is the same as that of B-PANI in Fig. 3.3A(a),

suggesting that dedoping was ineffective, which is consistent with the forthcoming XPS results,

while the spectrum of RB-PANI (Fig. 3.3B(b)) indicates the reduced form (LB)-PANI. In the

spectrum of DB-PANI (Fig. 3.3B (a)) the peak for the quinoid unit has a similar shift towards

lower wavelength as discussed earlier for Fig.3.3A (a) and (b). The UV/Vis spectrum of RB-

PANI (Fig. 3.3B(b)) shows an increase in the intensity of peak for benzenoid unit, and decrease

47

in the intensity of peak for quinoid unit, which is consistent with reduction to the LB-PANI form

[94].

Fig. 3.3C shows the UV absorption spectra of PANI and its reduced form R-PANI. In the

R-PANI (Fig. 3.3C (b)) the absorption peak for the quinoid unit at around 600-650 nm tends to

disappear relative to that of PANI (Fig. 3.3C (a)), which indicates the reduction of the sample to

the LB-PANI form [94]. Both PANI and R-PANI were obtained from their precursors by

treatment with 35% N2H4 (Scheme 1); the fact that R-PANI was not produced directly from the

B-PANI is attributed to the fact that all the N2H4 was used up in converting the basic copper(II)

chloride present in this sample to copper(I) chloride.

Fig. 3.3D shows the UV absorbance spectra of H-PANI, DH-PANI and RH-PANI.DH-

PANI (Fig. 3.3D (b)) and RH-PANI (Fig. 3.3D (c)) exhibit absorption at 320-330 nm and at

around 620-660 nm, which is similar to the emeraldine (EB) form of polyaniline [92]. In the RH-

PANI (Fig. 3.3D (c)) the peak at around 620-660 nm tends to disappear indicating the reduction

of EB to the LB form [94]. The conclusions from the UV absorption spectra of H-PANI, DH-

PANI and RH-PANI are in good agreement with those from the FTIR spectra.

3.4 Elemental Analysis

The elemental analysis results for the DB-PANI and H-PANI products are shown in

Table. 3.3. The C/N ratios are close to, but slightly higher than, the theoretical value of 6.0 for

PANI. The results given in the Table 3.3 for DB-PANI and H-PANI are given in the same form

as those for the EB form of PANI reported in Zeng et al. [90], i.e. it gives the ratio C:H:N

calculated from the elemental analysis data; however, there must be a significant amount of other

elements present as the sum of the C, H, N content is only 67%. The % of C,H,N values for

undoped EB-PANI add to 100% (Table 3.3), and are all considerably higher than the

experimental values for H-PANI and DB-PANI. If the PANI were present as ES-PANI with Cl-

as the dopant (i.e. the EB-PANI 2HCl salt), lower values would be obtained (Table 3.3), but

these are still significantly higher than the experimental values. Under the experimental

conditions used to produce these materials (excess CuCl2 in solution) it is possible that the

chloride dopant ions could associate with a CuCl2 molecule to produce a [CuCl4]2- dopant to

produce EB-PANI H2CuCl4 salt as the product, for which the calculated %C,H,N (Table 3.3) are

48

in much closer agreement with the observed values. In order to investigate this further, the H-

PANI and DB-PANI products were examined by XPS.

Table 3.3. Compositions of DB-PANI and H-PANI for oxidant to monomer ratio R = 15

Sample %C %H %N Composition C/N ratio

DB-PANI

H-PANI

EB-PANI

ES-PANI

(2HCl salt)

ES-PANI

(H2CuCl4 salt)

ES-PANI (30%

ox; 2HCuCl3 salt)

ES-PANI (30%

ox; 1.8HCuCl3

salt)

53.68

52.84

79.54

66.21

50.59

50.72

52.62

3.79

4.30

5.01

4.63

3.54

3.55

3.66

9.92

10.06

15.46

12.87

9.84

9.86

10.23

C24H20.23N3.80 +?

C24H23.44N3.91 +?

C24H18N4

C24H20Cl2N4

C24H20CuCl4N4

C24H20Cu1.2Cl3.6N4

C24H19.9Cu1.1Cl3.2N4

6.3

6.1

6.0

6.0

6.0

6.0

6.0

49

3.5 X-Ray Photoelectron Spectroscopy

Cu 2p XPS for H-PANI and DB-PANI are shown in Fig. 3.4. The spectrum of H-PANI

shows a strong Cu 2p signal which is completely absent in the DB-PANI product. The binding

energies of the Cu 2p3/2 and Cu 2p1/2 peaks at 933.4 eV and 953.3 eV (2:1 area ratio) are

characteristic for Cu(II), as are the characteristic shake up satellites ~7 eV above the main Cu 2p

lines. The satellite peak areas are ~36% of the total Cu 2p signal area. This is typical for copper

(II) containing compounds such as CuO. NH4OH treatment of the B-PANI product removed all

of the copper(II), whereas HCl treatment of the same material did not. This is consistent with

proposal above that the PANI formed in the CuCl2 oxidative polymerization is in the form of the

EB-PANI H2CuCl4 salt. The copper(II) that is contained in B-PANI would not be removed by

treatment with HCl, and it would still be present in the H-PANI product, but it would be

removed (as [Cu(NH3)4]2+ 2Cl-) by treatment with NH4OH, and would therefore be absent in the

DB-PANI product, as observed experimentally. Also consistent with this, is the fact that the XPS

data also showed the presence of Cl, and that the Cl content is reduced in the DB-PANI product.

However, the Cl/Cu ratio in H-PANI estimated from the XPS signal intensities (2.6) is closer to

3 as compared to the value 4 expected if the dopant were [CuCl4]2-. This suggests that the dopant

is [CuCl3]- (or an oligomeric or polymeric form thereof), and that the material is therefore the

EB-PANI 2HCuCl3 salt. [CuCl3]- would be a more likely dopant than [CuCl4]

2- under the

conditions of the synthesis (excess CuCl2 present) However, this does not provide a good

agreement with the composition determined by elemental analysis as the %C, H, N values for

this form is too low. The surface sensitivity of the XPS technique may be responsible for the

discrepancy in the Cl/Cu ratio. The XPS signal comes from the top 1-2 nm of the PANI samples.

Surface leaching of chloride during post synthesis washings could have partially removed

chloride from the near surface region of the samples (while leaving the bulk composition

determined by elemental analysis largely unaffected).

50

Figure 3.4. Cu 2p XPS for (a) H-PANI, and (b) DB-PANI.

A further variable relevant to the composition of PANI materials is the degree of

oxidation (or oxidative doping level) and this can be determined by XPS by examining the

oxidation states of N present, via the N 1s [95] signal. N 1s XPS for H-PANI and DB-PANI are

shown in Fig. 3.5. The N 1s data for both samples can be fitted using a combination of sub-

spectra due to oxidized (-NH2+-, =NH+-) and neutral (-NH-, =N-) nitrogen environments. Results

of the curve-fitting are shown in Table 3.4 which indicates a degree of oxidation of ca. 0.3 for

both products. The fact that the same value is obtained for both is consistent with the expectation

that acid/base doping/dedoping should not change the degree of oxidation. The degree of

oxidation is less than the value 0.5 corresponding to the ES-PANI form, and this is consistent

51

with the expectation that a weaker oxidant such as CuCl2 might not achieve as high a degree of

oxidation as a stronger oxidant such as APS. The degree of oxidation also determines the

maximum level of acid doping. Combination of the results of the XPS analyses for the H-PANI

product (30% oxidation, [CuCl3]- dopant) results in the composition [(C12H10N2)1-

x(C12H10N22+)x[CuCl3

-]2x with x = 0.3. This yields % C, H, N values that are in reasonable

agreement with the observed values (Table 3). Further improvement in the agreement is obtained

if the possibility of partial doping of the polymer is considered. It is well known that EB PANI

can only be fully acid doped (2H+ per two oxidized N atoms) in solutions of low pH, near pH = 0

[24] In the CuCl2 oxidation experiments, the pH only fell to 1.7 in the R = 15 case. Therefore,

the degree of doping would be expected to be less than 2HCuCl3 per two oxidized N atoms. In

the last row of Table 3.3 the results for 1.8CuCl3 per two oxidized N atoms have been added,

resulting in much better agreement with the observed %C, H, N values.

52

Figure 3.5. N 1s XPS for (a) H-PANI, and (b) DB-PANI.

53

Table 3.4. Speciation of Nitrogen in PANI samples from N 1s Peak Analysis

Sample Percentage of total N Nox/Ntotal

2HN

402.5 eV

HN

401.1 eV

NH

399.7 eV

N

398.4 eV

H-PANI 4.7 23.5 52.8 19.0 0.28

DB-PANI 7.4 22.9 63.2 6.5 0.32

3.6 Soft X-ray Spectroscopy

Fig. 3.6 shows the nitrogen K edge NEXAFS spectra of (a) B-PANI, (b) DB-PANI, and

(c) RB-PANI. The spectra contain an intense feature at around 397.4 eV, in B-PANI, DB-PANI

and RB-PANI which is likely to arise from the =N- quinoid ring of the emeraldine base form

[96]. The intensity of this peak for the quinoid unit of polyaniline in the RB-PANI is less

compared to those of B-PANI and DB-PANI, which confirms that the sample has been reduced.

This is supported by the fact that the peak at 402.3 eV gains intensity as the peak at 397.4 eV

peak was attenuated. The 400.1 eV peak is assigned to the three electron =N--bonding in the

emeraldine base form of PANI [96]. The 402.3 eV peak is due to -NH- in PANI emeraldine base

forms[96]. The broad peak above 406 eV is due to delocalized sigma* resonances [97]. The

observations in Fig. 3.6 are consistent with those seen in the FTIR and UV/Vis for these

materials.

54

Figure 3.6. NEXAFS of (a) B-PANI (b) DB-PANI (c) RB-PANI.

3.7 Solid state NMR

Fig. 3.7 shows the solid state 13C NMR of the sample DH-PANI. The solid state NMR

spectra show peaks at 118.580, 130.163, 133.472, 142.296 and 155.533 ppm. Based on previous

related work [98-101] the assignment of these peaks is shown in Table 3.5 which are similar to

the EB form of PANI reported in literature. The peak at 118.580 and 130.163 ppm are assigned

to C-6 and C-2,3 respectively. The peaks for the C-7,8 of the quinoid unit of EB PANI appear at

155.533 and 133.472 respectively. The peak at 142.296 is assigned to C-4,5.

55

Figure 3.7. 13C Solid State NMR spectra of DH-PANI.

Table 3.5.Peak assignment in the SSNMR of EB form of PANI

* NH NH Nn

N

2 3

3

1

2

4 5

6

6

5 4

3

36

6

2

2

1 7

8

8

8

8

7

13C chemical shift Assignment (carbon number)

118.580 C-6

130.163 C-2, 3

133.472 C-8 Quinoid unit

142.296 C-4, 5

155.533 C-7 Quinoid unit

56

3.8 SEM Analysis

The SEM images of B-PANI, H-PANI and DB-PANI are shown in Fig. 3.8 (a), (b) and

(c) respectively. The images show the spherical morphology of particles as reported in previous

literature [17]. In the work reported by Ding et al. [102], they have prepared PANI nanofibers

whereas we have obtained the PANI nano particles. The average particle size of B-PANI and H-

PANI is 660 nm, 350 nm respectively. The material is highly porous and has irregular pore size

[103].

Figure 3.8. SEM analysis of (a) B-PANI, (b) H-PANI, and (c) DB-PANI.

56

3.8 SEM Analysis






[103].


56

3.8 SEM Analysis






[103].


57

3.9 Mechanism of PANI formation

A proposed mechanism of PANI formation by oxidation of aniline with copper chloride

is as follows: (see Figure 3.9)

4C6H5NH2 + 10 CuCl2 {[-C6H4-NH-]4}2+ + 8H+ + 10 CuCl2

-

where {[-C6H4-NH-]4}2+ is the emeraldine salt form of PANI the structure of which is given

below

Figure 3.9. Mechanism of PANI formation.

This differs from the mechanism reported in literature for the corresponding reaction

involving gold(III) chloride, in which the gold(III) is reduced to gold metal [17]. While the

formation of copper metal in the reaction of aniline with copper(II) has been proposed previously

[84], this seems unlikely in the present case because a rather strong reducing agent is required to

reduce copper(II) to copper(0), and in protic solvents copper(II) and copper(0) comproportionate

to copper(I). In the present study, the XPS showed that the copper in the product was present as

copper(II). If the above reaction were stochiometric, the dopant would be CuCl2- (copper(I))

rather than CuCl3- (copper(II)). However, because CuCl2 is in large excess in the reaction

mixture, copper(II) is more likely to be incorporated in the dopant anion than copper(I).

58

3.10 Results and Discussion (Part II)

3.11 pH measurement along with mass yield

Table 3.6 shows the mass of product relative to the mass of aniline monomer and the

oxidant to monomer ratio of the reactions. A decrease in final pH and the corresponding increase

in the yield of reactions were observed as the concentration of CuCl2 increases in the reaction

mixture. This increase in the yield is most likely due to an increase in the oxidation potential of

CuCl2 with an increase in its molar concentration [88].

Table 3.6. Oxidant to Monomer Ratio and Mass Yield along with initial and final pH

Oxi/Mon Initial pH Final pH Mass yield in grams

0.05 4.72 4.58 0.0171

0.25 4.85 4.60 0.0280

0.50 4.83 4.47 0.0342

0.75 4.70 4.37 0.0263

1.0 4.75 4.23 0.0373

1.25 4.71 4.10 0.0342


The FTIR spectra for pure emeraldine base (EB) and L-PANI samples are shown in

Fig.3.10 (a) and (b) respectively. The spectrum of pure EB shows intense peaks at 1585 and

1493 cm-1 which are assigned to the quinoid and benzenoid unit of polyaniline respectively. In

case of L-PANI sample the peak for the quinoid unit of polyaniline is absent while that of

benzenoid unit is shifted to1469 cm-1. The C-N stretching mode in L-PANI (Fig.3.10 b) is shown

by peak at 1209 cm-1 [33], while the C-H out of plane bending is shown by peak at 866 cm-1 [18].

In L-PANI (Fig. 3.10 b) another intense peak at 1290 cm-1 indicates the presence of secondary

amine [32]. From the FTIR spectra it is evident that the product L-PANI is the fully reduced

leucoemeraldine form of PANI.

59

Figure 3.10. FTIR spectra of (a) pure EB (b) L-PANI.

3.13 UV/Vis Spectroscopy

The UV/Vis spectra of polyaniline EB form shows strong absorption in the region from

320-340 nm and 600-660 nm which is due to the presence of benzenoid and quinoid units of

polyaniline [92]. The UV/ Vis spectra of pure EB and L-PANI sample are shown in Fig.3.11 (a)

and (b) respectively. The UV/Vis spectra of pure EB has two peaks at 629 and 324 nm while in

case of L-PANI sample the peak for the quinoid unit is absent indicating that the L-PANI sample

is the fully reduced leucoemeraldine form of PANI. The information provided by the UV/Vis is

in agreement with the FTIR spectra in Figure 3.10.

60

Figure 3.11. UV/Vis spectra of (a) pure EB (b) L-PANI.

3.14 Elemental Analysis

Table.3.7 shows the results of elemental analysis of L-PANI sample. The percentage of C,

H and N were found to be 76.87, 5.64 and 15.20 respectively, which are close to the theoretically

calculated values for leucoemeraldine form of polyaniline. The percentage of hydrogen is found to

be more than expected which may be due to the presence of water molecule [90]. The C/N ratios

from elemental analysis are close to the expected value of 6.0.

Table 3.7. Elemental Analysis Results of L-PANI

Sample Oxi/Mon %Yield % C % H % N Composition C/N ratio

L-PANI 1 23 76.87 5.64 15.20 C24H20.06N4.07.(H2O)0.5 5.89

61

3.15 Results and discussion (Part III)

3.16 Mass yield and conductivity measurements

Table 3.8 shows the calculated mass yield for various PANI-Cu products and their

conductivities measured by four point probe instrument. Table1 shows that the mass yield of the

composite PANI-Cu decreases as the molar concentration of CuCl2 solution increases in the

reaction mixture. This decrease in mass yield may be attributed to the formation of copper

aniline complex [87] in addition to the formation of PANI-Cu products. The conductivity data

shows the decrease in conductivity of the composite which could be attributed to the partial

blocking of conductive path by Cu particle in the PANI matrix [104, 105], however, these values

are in good agreement with the data reported in [106].

Table 3.8. Mass Yield and Conductivity of PANI and its Composites with Cu

Sample Mass yield (g) Conductivity (S/cm)

PANI 0.192 1.92×10-2

PANI-Cu 0.2 0.0974 5.13×10-3

PANI-Cu 0.4 0.0664 2.14×10-4

PANI-Cu 0.5 0.0491 4.34×10-4

PANI-Cu 0.6 0.0133 4.81×10-4

PANI-Cu 0.7 0.0123 4.83×10-4

3.17 UV/Visible Spectroscopy

The UV/Vis spectra of polyaniline show strong absorption in the region from 320-330

nm and 600-660 nm. These peaks are assigned to the π−π* and n−π* transition of the benzenoid

and quinoid units of polyaniline respectively [92].

The UV/Vis spectra of PANI, PANI-Cu 0.2, PANI-Cu 0.4, PANI-Cu 0.6 and PANI-Cu

0.7 are shown in Figure 3.12 (a), (b), (c), (d), and (e) respectively. The peaks at 326-328 nm

62

indicate the π−π* transition of benzenoid units of polyaniline [93]. In case of PANI-Cu 0.2,

PANI-Cu 0.4, PANI-Cu 0.6 and PANI-Cu 0.7 the peak for the quinoid units of polyaniline has a

blue shift. This blue shift may be attributed to the presence of Cu II chromophores. The spectra

also indicate that the blue shift becomes more prominent with the increase in CuCl2

concentration. Such kind of blue shift has been reported for the presence of TiO2 in polyaniline

by Karim et al. [107].

Figure 3.12. UV/Vis spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, (d) PANI-Cu 0.6and (e) PANI-Cu 0.7.


Figure 3.13 shows the FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, and

(d) PANI-Cu 0.6. In Fig. 3.13 (a), (b), (c), and (d) the peaks at around 1492 and 1581 cm-1 are

attributed to the benzenoid and quinoid unit of polyaniline. The bands at 1232 and 1301 cm-1 are

attributed to the C=N and C-N stretching modes. The peaks at 829 and 1139 cm-1are assigned to

the C-H out-of-plane and in-plane bending mode [17]. In Fig. 3.13 (b), (c) and (d) the peak for

quinoid unit at 1581 gains intensity as the concentration of CuCl2 increases in the reaction

mixture indicating the interaction of CuCl2 with the nitrogen atom of quinoid unit of polyaniline

[108], however, in our case the peak for quinoid unit of PANI has not been blue shifted, which

63

may be due to the low concentration of CuCl2 solutions and co-formation of Cu-aniline complex,

as discussed earlier. The FTIR spectra are mostly dominated by the polyaniline signals and thus

the polymer-metal interaction is not very clear [20].

Figure 3.13. FTIR spectra of (a) PANI, (b) PANI-Cu 0.2, (c) PANI-Cu 0.4, and (d) PANI-Cu0.6.

3.19 Thermogravimetric Analysis (TGA)

The thermal stability of synthesized PANI and PANI-Cu was tested by using TGA. The

samples were kept for one minute at 30 oC and then heated from 30 °C to 600 oC at a rate of 10oC/minute. The loss in mass for PANI and PANI-Cu composite upon heating under nitrogen

atmosphere is shown in Fig. 3.14 (a) and (b) respectively. A steady mass decrease is found up to

296oC both in case of PANI Fig.3.14 (a) and PANI-Cu Fig.3.14 (b). A rapid change in mass

occur in the range from 300-400oC in both the samples but in case of PANI the % weight loss is

more as compared to PANI-Cu which indicates greater stability of PANI-Cu as compared to

PANI. The weight lost at low temperature is attributed to the expulsion of water from the

polymer structure while at high temperature the degradation of polymer chain takes place due to

the removal of acid dopant. After the removal of acid dopant the decomposition of polymer

skeleton occurs at even higher temperature [109]. The weight loss of PANI and PANI-Cu

64

composite at 600oC was 68.06% and 42.01% respectively. The data indicate the improvement in

the thermal stability due to the inculcation of metal particles in the PANI matrix [107].

Figure 3.14. TGA analysis of (a) PANI and (b) PANI-Cu.

3.20 X-ray Diffraction (XRD)

The XRD is a nondestructive and helpful technique used to identify the crystallinity of

solid materials. Fig. 3.15 (a) and (b) show the XRD of PANI and PANI-Cu respectively. For

PANI and PANI-Cu the characteristic peak appears at 2θ = 25o, 19o and 13o indicating that both

the samples were amorphous [16]. Since the XRD peaks for PANI-Cu are mostly similar to that

of the free PANI so this suggests that the structure of CuCl2 may be distorted during the process

of polymerization [110], moreover, the peaks for PANI sample are slightly sharper than PANI-

Cu which suggests that the PANI sample is more crystalline than PANI-Cu. This is in agreement

with the conductivity data as discussed in Section 3.16 (Table 3.8).

65

Figure 3.15. XRD analysis of (a) PANI and (b) PANI-Cu.

3.21 Scanning Electron Microscopy (SEM)

The SEM images of PANI and PANI-Cu are shown in Fig. 3.16 (a) and (b) respectively.

The PANI sample i.e Fig. 3.16 (a) has an uneven irregular surface morphology as reported in

previous literature [57]. In case of PANI-Cu, Fig. 3.16 (b) the irregularity of surface has

increased and appears to be more porous than PANI [111]. The pore size in PANI-Cu is uneven

and larger as compared to PANI. Although the surface morphology of the composite PANI-Cu

does not differ much from the pure PANI, when CuCl2 is added, the pore size of composite

become larger, which leads to the change in morphological structure from firm gravel to lose

cotton appearance.

66

Figure 3.16. SEM images of (a) PANI and (b) PANI-Cu.

3.22 Cyclic voltammetry (CV)

Cyclic voltammetry (CV) was carried out to study the redox properties of synthesized

material by using gold as working electrode. The calomel electrode was used as reference. On

the gold foil electrode a thin film of the polymer was deposited and the CVs were recorded with

a scan rate of 50 mV S-1 in 0.5M H2SO4 solution as supporting electrolyte.

The cyclic voltamograms of the synthesized PANI and PANI/PVA composite are shown

in Fig. 3.17 (a) and (b) respectively. The PANI sample, Fig. 3.17 (a), shows two redox peaks (I

and II). The conversion of fully reduced neutral leucoemeraldine (LE) form of PANI to partially

oxidized emeraldine base (EB) form of PANI is shown by the peak at ESCE= 0.109V, while the

conversion of partially oxidized EB form to the fully oxidized pernigraniline state of PANI is

shown by the peak at ESCE= 0.650V [112, 113]. In the reverse scan the conversion of

pernigraniline to emeraldine and then from emeraldine to leucoemeraldine state is shown by the

peak I/ and II/ at ESCE= -0.046V and ESCE= 0.6130V respectively [57]. The peak I and II in case

of PANI-Cu appears at ESCE= 0.104V, and ESCE= 0.63V respectively which are slightly shifted

toward the left indicating the presence of metal in the sample [114]. In the reverse scan the peaks

I/ and II/ appear at ESCE= 0.0180V and ESCE=0.594V respectively for PANI-Cu composite. The

cyclic voltamogram of PANI-Cu shows that the composite is electro active and show two

oxidation/reduction peaks just like PANI [114].

67

Figure 3.17 CVS of (a) PANI and (b) PANI-Cu.

3.23 In situ UV/Vis Spectroscopy

The UV/Vis spectra of PANI and PANI-Cu film, deposited on ITO coated glass electrode

at various electrode potentials ERHE = 0.0 to 0.8 is shown in Fig. 3.18 (a) and (b) respectively.

Three characteristic absorption bands can be seen. The band at around λ= 315 nm is attributed to

the π−π* transition of the benzenoid units of reduced PANI [115, 116]. This peak is shifted to

360 nm in the spectra of PANI-Cu product. The band at λ= 420 nm showing maximum intensity

at ERHE = +0.3 is attributed to an intermediate redox state of the PANI film, which possibly

possesses non conjugated benzenoid units in a polymer chain [115-119]. In the red region of the

UV/Vis spectra the main absorbance band is assigned to the emeraldine form of PANI. This peak

is also shifted towards the lower wavelength with increase in potential as reported earlier [119].

A decrease in the intensity of the band at λ= 315 nm and a progressive increase in the intensity of

the band in the red region is observed by shifting the electrode potential to higher values,

indicating a decreasing number of benzenoid rings and increasing number of quinoid rings

because of oxidation of the leucoemeraldine into the emeraldine form of PANI. This behavior is

more prominent in PANI as compared to PANI-Cu product.

68

Figure 3.18. UV-Vis spectra of (a) PANI and (b) PANI-Cu film, deposited on ITO coated glass

electrode, obtained at different electrode potential values ranging from ESCE= 0.0 TO 0.8 V at an

interval of 0.1 V.

Fig. 3.19 (a) and (b) show the dependence of absorbance on potential at three different

wavelengths [(315 and 360 nm), 420 nm, and 750 nm] derived from Fig.3.18 (a) and (b). A

decrease in absorbance at λ= 315 and 360 nm is observed by sweeping the potential to higher

values which is attributed to the conversion of benzenoid segments to quinoid segments of

69

PANI [115]. The absorbance maxima for the band at λ= 420 nm is observed at around ERHE =

+0.3 V which is assigned to the intermediates formed during the electro oxidation of

leucoemeraldine form of PANI [117-119]. A progressive increase in the absorbance band at λ=

750 nm with the increase in potential indicates the increase in quinoid units of emeraldine form

of PANI [119].

Figure 3.19. (a) and (b) Absorbance vs. Potential at three selected wavelengths, derived

from the above displayed spectra in Fig. 3.18 (a) and (b).

70

3.24 Results and Discussion (Part IV)

3.25 Conductivity Measurements and Mass Yield

The mass yield calculated for various PANI/PVA products and their conductivity

measurement by four probe instrument are shown in Table 3.9. The results in Table 3.9 show

that the mass yield of the PANI/PVA decreases as the percentage of PVA solution increases in

the reaction mixture. This decrease in mass yield may be attributed to hydrogen bonding between

hydrogen of hydroxyl group of PVA and nitrogen of aniline due to which the aniline

polymerization is inhibited [120]. The conductivity data obtained from the four point probe

instrument show that the composite containing 3% PVA has maximum conductivity i.e.

6.66×10-2 S/cm. This is further supported by the XRD data (see below, Fig. 3.23 (b) PANI/PVA)

that the conductivity increases with the increase in crystallinity [121]. Beyond 3% PVA content,

the conductivity of the composite decreases which can be attributed to the increase of non

conducting PVA content with respect to conducting PANI contents in the composite [122, 123].

Table 3.9. Mass Yield and Conductivity of PANI and its Composites with PVA

Sample Mass yield (g) Conductivity (S/cm)

PANI 0.1927 1.9×10-2

PANI/PVA 1% 0.1259 2.46×10-2

PANI/PVA 2% 0.1640 4.99×10-2

PANI/PVA 3% 0.1373 6.66×10-2

PANI/PVA 4% 0.1368 5.35×10-2

PANI/PVA 5% 0.1010 5.27×10-2

PANI/PVA 6% 0.1130 5.27×10-2

71

3.26 UV/Visible spectroscopy

The UV/Vis spectra of PANI and PANI/PVA are shown in Figure 3.20. The peaks at 326

and 633 nm [Fig.3.20 (a)] indicate the π−π* transition of benzenoid and quinoid segments of

polyaniline [93]. In PANI/PVA [Fig.20 (b)] these peaks for π−π*are red shifted to 335 and 645

nm respectively. This red shift may be attributed to the doping of PVA in PANI matrix [124].

Figure 3.20. UV/Vis spectra of (a) PANI and (b) PANI/PVA.


Figure 3.21 (a) and (b) show the FTIR spectra of PANI and PANI/PVA respectively. The

characteristic bands in the spectrum of PANI [Fig. 3.21 (a)] are observed at 1581, 1508, 1311,

1138, 1028 and 827 cm-1. The frequency bands at 1581 and 1508 cm-1 are due to the presence of

quinoid and benzenoid ring of polyaniline respectively [17, 125]. The peak at 1311 cm-1 is

attributed to the C-N stretching mode of secondary aromatic amine [126]. The band at 1138 cm-1

has been assigned to the vibration of Q=+NH-B representing that the product PANI is in the

conductive emeraldine salt form of polyaniline [127]. The band at 1028 cm-1 is assigned to the

absorption of –SO3H group indicating that the PANI sample is also doped with DBSA. The peak

at 827 cm-1 is assigned to the C-H out-of-plane bending vibration [125]. The spectrum of

PANI/PVA shows all the characteristic peaks corresponding to the PANI spectrum and did not

72

show any additional peak thereby giving indication of no chemical interaction between PANI

and PVA [123]. However, in PANI/PVA spectrum the peak for the quinoid segment of

polyaniline is shifted from 1581 cm-1 to 1595 cm-1 which indicates the presence of hydrogen

bonding between PANI and PVA [120]. The FTIR spectra of PANI and PANI/PVA are

consistent with the UV/Vis spectra of PANI and PANI/PVA in Fig.3.20.

Figure 3.21. FTIR spectra of (a) PANI and (b) PANI/PVA.

3.28 Thermogravimetric Analysis (TGA)

Thermo gravimetric analysis (TGA) was performed to study the thermal stability of

synthesized PANI and PANI/PVA composite. The samples were heated from 30oC to 600 oC at a

rate of 10oC/minute after holding them for one minute at 30 oC. Fig.3.22 shows the loss in mass

for PANI and PANI/PVA composite upon heating under nitrogen atmosphere. A steady mass

decrease is observed up to 297 oC in both PANI (Fig.3.22 (a)) and PANI/PVA (Fig.3.22 (b)).

From 300-400oC a rapid change in mass is observed in both the samples but in case of

PANI/PVA the % weight loss from 350-400 oC is more as compared to PANI which indicates

that the stability of PANI is higher than that of PANI/PVA in the said temperature range. Beyond

400 oC the stability of PANI/PVA composite is greater as compared to PANI as the overall mass

loss in PANI/PVA is less than PANI. At low temperature the weight lost is attributed to the

removal of water from the polymer structure while the degradation of polymer chain takes place

73

at higher temperature due to the removal of acid dopant. At even higher temperatures, the

decomposition of polymer skeletal occurs after the removal of acid dopant [109]. The TGA

indicates the improvement in the thermal stability due to the incorporation of PVA in PANI

[124].

Figure 3.22. TGA curve of (a) PANI and (b) PANI/PVA.

3.29 X-ray Diffraction (XRD)

Most of the polymers are amorphous due to large volume fraction of amorphous phases.

Generally both PANI and PVA are amorphous. Fig.3.23 (a) and (b) show the XRD pattern of

PANI and PANI/PVA respectively. The PANI/PVA show the characteristic peak of PVA at

2θ=20o which confirms the presence of PVA in PANI [124]. The PANI and PANI/PVA samples

have peaks at 2θ=12o, 20o and 25o showing the amorphous nature [16]. However, the peak at

2θ=25o is more intense in PANI/PVA thus the crystallinity of PANI/PVA is increased by the

insertion of PVA [10]. This is further supported by the fact that the conductivity of PANI-PVA

has increased (see , Table 3.9) with the increase in crystallinity.

74

Figure 3.23. XRD of (a) PANI and (b) PANI/PVA.

3.30 Scanning Electron Microscopy (SEM)

Fig. 3.24 (a) and (b) show the SEM images of PANI and PANI/PVA respectively. The

SEM image of PANI [Fig.3.24 (a)] shows an irregular morphology. The irregular morphology of

PANI is also reported elsewhere [57]. From the SEM images it is quite clear that small granules

of PVA are present in the PANI matrix and the morphology of PANI is different from that of

PANI/PVA. The SEM image of PANI/PVA composite shows irregular shaped particles with

variable size. The irregular shape of PANI/PVA composite is attributed to the non compatibility

of two components [128]. Moreover, the PANI/PVA is more porous as compared to PANI [103,

129]. The surface of PANI is smoother than PANI/PVA and the sharp edges of PANI/PVA

particles can easily be correlated with the XRD data as discussed above (Fig. 3.23 (a), (b)). The

average particle size of PANI/PVA is 4 μm.

75

Figure 3.24. SEM images of (a) PANI and (b) PANI/PVA.

3.31 Cyclic Voltammetry (CV)

In order to investigate the redox properties of synthesized material cyclic voltammetry

(CV) was carried out by using gold as working electrode. Fig. 3.25 (a) and (b) show the cyclic

voltamograms of the synthesized PANI and PANI/PVA composite. The PANI sample show two

redox peaks (I and II). The peak at ESCE= 0.109V corresponds to the conversion of fully reduced

neutral leucoemeraldine form of PANI to partially oxidized emeraldine base (EB) form of PANI

while the peak at ESCE= 0.650V is due to the conversion of partially oxidized EB form to the

fully oxidized pernigraniline state of PANI [112, 113]. In the reverse scan peak I/ at ESCE= -

0.046V and II/ at ESCE= 0.6130V are attributed to conversion of pernigraniline to emeraldine and

then from emeraldine to leucoemeraldine state [57]. In case of PANI/PVA the peak I appears at

ESCE= 0.0830V, while the peak II retains its position at 0.65V. In the reverse scan the peak I/ and

II/ appears at ESCE= 0.0180V and 0.6380V for PANI/PVA composite. From the cyclic

voltamograms we can conclude that the PANI/PVA composite is electro active and show two

oxidation/reduction peaks just like PANI [130].

76

Figure 3.25. CVs of (a) PANI and (b) PANI/PVA on gold foil electrode (vs SCE) in 0.5MH2SO4.

3.32 In situ UV/Visible Spectroscopy

Fig. 3.26 (a) and (b) show the UV/Vis spectra of PANI and PANI/PVA film, deposited on ITO

coated glass electrode respectively. The various electrode potentials for both the samples are

ERHE = 0.0 to 0.8 V. In the absorption spectra of PANI the band at around λ= 315 nm is assigned

to the π−π* transition of the benzenoid segment of reduced PANI [115, 116]. This peak is shifted

to 360 nm in the spectra of PANI-Cu product. The band at λ= 420 nm in both PANI and PANI-

PVA having maximum intensity at ERHE = +0.3 V is related to an intermediate redox state of the

PANI film, which possibly possesses non conjugated benzenoid units in a polymer chain [115-

119]. The main absorbance band in the red region of the UV/Vis spectra of both PANI and

PANI/PVA is assigned to the emeraldine form of PANI. This peak is also shifted towards the

lower wavelength with increase in potential as reported earlier [119]. In PANI sample a decrease

in the intensity of the band at λ= 315 nm and a progressive increase in the intensity of the band in

the red region is observed by shifting the electrode potential to higher values, indicating a

decreasing number of benzenoid units and increasing number of quinoid units because of

oxidation of the leucoemeraldine into the emeraldine form of PANI. This behavior is more

prominent in PANI as compared to PANI/PVA product.

77

Figure 3.26. UV/Vis spectra of (a) PANI and (b) PANI/PVA film, deposited on ITO coated

glass electrode, obtained at different electrode potential values ranging from ESCE= 0.0 TO 0.8 V

at an interval of 0.1 V.

The dependence of absorbance on potential at different wavelengths i.e 315 nm, 420 nm, and 750

nm for PANI and 420 nm and 750 nm for PANI/PVA derived from Fig.3.26 (a) and (b) are

shown by the graph in Fig. 3.27 (a) and (b) respectively. In case of PANI a decrease in

absorbance at λ= 315 and 360 nm is observed by sweeping the potential to higher values which

78

is assigned to the conversion of benzenoid segments to quinoid segments of PANI [115]. The

absorbance maxima for the band at λ= 420 nm is observed at around ERHE = +0.3 V which is

assigned to the intermediates formed during the electro oxidation of leucoemeraldine form of

PANI [117-119]. A progressive increase in the absorbance band at λ= 750 nm with the increase

in potential indicates the increase in quinoid segments of emeraldine form of PANI [119].

Figure 3.27 (a) and (b) Absorbance vs. Potential at three selected wavelengths, derived from the

above displayed spectra in Fig 3.26. (a) and (b).

79

3.33 Results and Discussion (Part V)

3.34 Conductivity Measurements and Mass Yield

Table 3.10 shows the mass yield and conductivity measurements of PANI, PANI-Cu,

PANI-PVA, and PANI-Cu-PVA. The conductivity of the three component system i.e PANI-Cu-

PVA is greater than the conductivity of pure PANI, PANI-Cu, and PANI-PVA as shown by

Table 3.10. The conductivity of two component system comprising of PANI-Cu is less than the

conductivity of alone pure PANI and two component PANI-PVA system. The Cu particles

embedded in the PANI matrix are responsible for the decrease in conductivity of PANI-Cu

because they partially block the conductive path present in the neat PANI [105]. This is further

confirmed by the XRD data shown in Fig. 3.31 (b) where the crystallinity of PANI-Cu is less

than the rest of the samples.

Table 3.10. Mass Yield and Conductivity Measurements

Sample Mass yield (g) Conductivity(S/cm)

PANI 0.1947 1.92×10-2

PANI-Cu 0.0979 5.12×10-3

PANI-PVA 0.1423 6.65×10-2

PANI-Cu-PVA 0.1243 1.04×10-1

80

3.35 UV/Visible Spectroscopy

The UV/Vis spectra of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in Fig.3.28

(a), (b), (c), and (d) respectively. The UV/Vis spectra of PANI [Fig. 3.28 (a)] and PANI-PVA

[Fig.3.28 (c)] show two peaks at around 330 nm and 640 nm which are assigned to the π−π*

transition of benzenoid and n−π* transition of quinoid units of polyaniline respectively [92]. In

case of PANI-Cu [Fig.3.28 (b)] the peak for the quinoid unit is shifted towards the lower

wavelength at around 560 nm which could be due to the presence of Cu II chromophores [107].

In case of the three components system i.e PANI-Cu-PVA [Fig.3.28 (d)] the peak for quinoid

unit appears at around 580 nm which is red shifted as compared to PANI-Cu and blue shifted as

compared to both PANI, and PANI-PVA. A shoulder peak at around 280 nm in both PANI-Cu

and PANI-Cu-PVA is also present which is indicative of the presence of Cu II [107]. This peak

at 280 nm is absent in both PANI and PANI-PVA.

Figure 3.28. UV/Vis spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.


The FTIR spectra of PANI, PANI-Cu, PANI-PVA, and PANI-Cu-PVA is shown in Fig. 3.29 (a),

(b), (c), and (d) respectively. The benzenoid and quinoid unit of polyaniline are shown by the

81

peaks at around 1498 and 1582 cm-1. The C-N and C=N stretching modes are shown by the

bands at 1307 and 1230 cm-1 respectively [17]. The C-H in-plane and out-of-plane bending

modes are evident from the peaks at 1139 and 826 cm-1 respectively [17]. In case of PANI-Cu

the intensity of quinoid unit is more as compared to all other samples which indicates the

interaction of Cu with the nitrogen atom of imine units of polyaniline [108], however the

expected blue shift of the quinoid peak is not observed in our case which may be attributed to the

co- formation of Cu aniline complex [87] and low molar concentration of CuCl2 solution in the

reaction mixture. In case of PANI-PVA there is no significant change in the position and

intensity of peaks for the quinoid and benzenoid units of polyaniline, thus there is no chemical

interaction of PVA with PANI [123]. In case of three components PANI-Cu-PVA system, a

significant decrease is observed in the intensity of peaks for the amine and imine units of

polyaniline.

Figure 3.29. FTIR spectra of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.

3.37 Thermo gravimetric Analysis (TGA)

Thermo-gravimetric analysis was carried out to test the thermal stability of the synthesized

materials. The TGA curves for PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in

Fig. 3.30 (a), (b), (c), and (d) respectively. Fig. 3.30 shows that the loss in mass from 30 to 300

82

oC in the PANI-Cu, PANI-PVA and PANI-Cu-PVA is almost the same and less than that of neat

PANI. This loss in mass is attributed to the removal of water molecules from the polymer chain

[109]. From 300-400 oC a greater mass loss is observed in all the samples which is attributed to

the removal of acid dopants from the polymer structure [109]. The degradation of polymer chain

starts at even higher temperature for all the samples [109] and at 600oC the % mass loss for

PANI (98.56%) is greater than the % mass loss of the PANI-Cu (53.17%), PANI-PVA (67.94%)

and PANI-Cu-PVA (72.11%). This indicates that the thermal stability of the composites of PANI

is more than the neat PANI [107, 124].

Figure 3.30 TGA analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.

3.38 X-Ray Diffraction

The XRD patterns of PANI, PANI-Cu, PANI-PVA and PANI-Cu-PVA are shown in Fig.3.31

(a), (b), (c) and (d) respectively. In comparison of PANI Fig.3.31 (a) and PANI-Cu, Fig.3.31 (b)

the characteristic peak for both appears at 2θ = 13o, 19o and 25o indicating that both the samples

are amorphous [16]. Since the XRD peaks for PANI-Cu are mostly similar to that of the free

PANI so this suggest that the structure of CuCl2 may be distorted during the process of

polymerization [110], moreover, the peaks for PANI sample are slightly sharper than PANI-Cu

83

which suggest that the PANI sample is more crystalline than PANI-Cu. This is consistent with

the conductivity data as discussed in table 3.10.

The PANI/PVA (Fig. 3.31 (c)) show the characteristic peak of PVA at 2θ=20o which confirms

the presence of PVA in PANI [124]. The PANI/PVA sample have peaks at 2θ=12o, 20o and 25o

showing the amorphous nature [16]. However, the peak at 2θ=25o is more intense in PANI/PVA

thus the crystallinity of PANI/PVA is more than PANI due to the insertion of PVA [10]. This is

supported by the fact that the conductivity of PANI-PVA has increased (see table 3.10) with the

increase in crystallinity.

Fig. 3.31 (d) shows the XRD pattern of PANI-Cu-PVA. In comparison the crystallinity of the

three component system PANI-Cu-PVA is less than PANI-PVA, comparable to neat PANI, and

greater than PANI-Cu. However, this observation is in contrast with the conductivity data

discussed in table 3.10 where the conductivity of the three component system is greater than any

of the other two component system and neat PANI itself.

Figure 3.31. XRD analysis of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.

84

3.39 SEM Analysis

Fig. 3.32 (a), (b), (c), and (d) shows the SEM images of PANI, PANI-Cu, PANI/PVA, and

PANI-Cu-PVA respectively. The surface morphology for PANI [Fig. 3.32 (a)] is un even and

irregular as reported in previous literature [57]. The PANI-Cu [Fig. 3.32 (b)] seems to be more

porous and irregular as compared to PANI [111]. The pore size in PANI-Cu is larger and uneven

as compared to PANI which leads to the change in morphological structure from firm gravel to

lose cotton appearance.

The SEM image of PANI/PVA [Fig.3.32 (c)] shows the presence of small granules of PVA in

the PANI matrix. The PANI/PVA composite show irregular shaped particles with variable size.

The non compatibility of two components is responsible for the irregular shape of PANI/PVA

composite [128]. Moreover, the PANI/PVA is more porous as compared to PANI [103, 129] and

PANI-Cu. In the PANI/PVA the sharp edges of particles can easily be correlated with the XRD

data as discussed in Fig 3.31 (c). The average particle size of PANI/PVA is 4μm.

Fig. 3.32 (d) shows the SEM image of the three component system PANI-Cu-PVA. The surface

of the three component system is smoother than PANI, PANI-Cu, and PANI-PVA. Similar

smooth morphology is reported for the three component system of PANI-PVA-NiO

nanocomposites [131].

85

Fig 3.32. SEM images of (a) PANI, (b) PANI-Cu, (c) PANI-PVA and (d) PANI-Cu-PVA.

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85


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85


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86

4. CONCLUSION

The synthesis of polyaniline by using copper (II) chloride as oxidant was investigated in

detail. The UV/Vis, FTIR, XPS, NEXAFS and SSNMR and elemental analysis showed that

polyaniline was formed in a partially oxidized form, partially protonated with [CuCl3]- as the

dopant counter ion. The results of SEM show the spherical morphology of particles. A decrease

in the final pH of the reaction solution and an increase in the reaction yield with an increase in

the oxidant to monomer ratio were observed. The increase in the yield of the reaction was

ascribed to an increase in the oxidation potential of CuCl2 with an increase in its molar

concentration. The low yield of the reaction was attributed to the co-formation of a copper(II)

chloride aniline complex. Although the mass yield of reaction was on the low side (ca. 10% or

less), the present work indicates that weak oxidizing agents, such as copper(II) chloride can be

used for the oxidative polymerization of aniline. Oxidation of aniline by transition metal salts has

been proposed as a method for producing polyaniline/metal composites [83], and the production

of polyaniline/copper composites by using copper(II) compounds as the oxidant has been

proposed [84, 132]. However, it is apparent from the present work that, in the absence of air, a

significant amount of polymerization only occurs if a large excess of the copper(II) compound is

used. Moreover, the presence of copper metal in the product seems unlikely. For example, in a

recently reported study [132], the presence of copper as copper metal in the product appears to

have been assumed rather that proven, and the amount of “copper” found (46.6 wt. %) is

considerably greater than the theoretical maximum amount (39.4%) for the proposed mechanism

involving reduction of copper(II) to copper(0). These observations indicate that considerable care

is required to identify the exact nature of the reaction products before claiming the synthesis of a

particular polyaniline/metal composite.

In the present work we are not advocating the use of copper(II) chloride as a suitable

oxidant for the bulk synthesis of PANI, because it clearly is not. Rather, we have shown the kind

of reaction conditions and product characterization methods that are necessary to obtain well-

characterized PANI and to determine the true nature of the copper that is incorporated in the

product.

87

Polyaniline synthesis was carried out by using CuCl2 as oxidizing agent. The results

obtained from the FTIR, UV/Vis and elemental analysis show the presence of polyaniline in the

leucoemeraldine form. A decrease in pH of the reaction mixture with increase in oxidant:

monomer ratio was observed. Similarly an increase in the yield of reaction with increase in

oxidant : monomer ratio was observed which was attributed to the increase in oxidation potential

with increase in the molar concentration of copper II chloride. The formation of leucoemeraldine

was attributed to the low oxidation potential of CuCl2.

An inverse emulsion polymerization method was used to investigate the synthesis and

characterization of polyaniline doped with Cu II chloride. The results show that polyaniline was

coordinated with Cu II chloride. The TGA results show an increased thermal stability for PANI-

Cu while the XRD data proposed relatively less crystallinity of the composite. A decrease in

crystallinity causes the decrease in conductivity of the PANI-Cu composite. The cyclic

voltamograms indicate that the composite material (PANI-Cu) is electroactive. The SEM result

shows an uneven morphology for PANI-Cu composite with large pore size as compared to

PANI.

The synthesis and characterization of polyaniline doped with polyvinylalcohol was

investigated by inverse emulsion polymerization. The results show the presence of EB form of

polyaniline doped with polyvinylalcohol. The TGA and XRD results show an increased thermal

stability and better crystallinity of the composite PANI/PVA. An increase in conductivity was

observed as the crystallinity of composite increases. The composite material (PANI/PVA) was

found to be electroactive as clear from the cyclic voltamograms.

Polyaniline (PANI), polyaniline doped with polyvinylalcohol (PANI-PVA), polyaniline

doped with copper (PANI-Cu) as well as polyaniline co-doped with polyvinylalcohol and copper

(PANI-Cu-PVA) were prepared under similar conditions by inverse emulsion polymerization.

The UV/VIS and FTIR were used to examine the chemical structure of synthesized products.

The SEM results show the smooth morphology for the three component system of PANI-Cu-

PVA in comparison to PANI, PANI-Cu and PANI-PVA. The thermal stability of PANI-Cu-PVA

was found to be greater than PANI and less than PANI-Cu and PANI-PVA as shown by TGA.

The XRD data confirms the amorphous nature of all the samples.

88

References

1. Shirakawa, H., et al., Synthesis of electrically conducting organic polymers: halogen derivatives ofpolyacetylene, (CH). Journal of the Chemical Society, Chemical Communications, 1977(16): p.578-580.

2. R. Mcneill, et al., Electronic conduction in polymers. Aust. J. Chem, 1963. 16: p. 1056-1075.3. Syed, A.A. and M.K. Dinesan, Review: Polyaniline—A novel polymeric material. Talanta, 1991.

38(8): p. 815-837.4. Ayad, M.M., et al., Phosphoric acid and pH sensors based on polyaniline films. Current Applied

Physics, 2010. 10(1): p. 235-240.5. Gupta, K., P.C. Jana, and A.K. Meikap, Optical and electrical transport properties of polyaniline–

silver nanocomposite. Synthetic Metals, 2010. 160(13–14): p. 1566-1573.6. Xia, Y.N., et al., One-dimensional nanostructures: Synthesis, characterization, and applications.

Advanced Materials, 2003. 15(5): p. 353-389.7. Dai, H., E.W. Wong, and C.M. Lieberf, Probing ESectncai Transport in Nanomaterials:

Conductivity of Individual Carbon Nanotubes. Nature, 1995. 376: p. 139.8. Kong, J., et al., Nanotube Molecular Wires as Chemical Sensors. Science, 2000. 287(5453): p.

622-625.9. Di Wei, et al., Electrochemical fabrication of a nonvolatile memory device based on polyaniline

and gold particles. Journal of Materials Chemistry, 2008. 18: p. 1853-1857.10. Bhadra, J. and D. Sarkar, Electrical and optical properties of polyaniline polyvinyl alcohol

composite films. Indian Journal of Pure and Applied Physics, 2010. 48(June): p. 425-428.11. Rupali Gangopadhyay, A.D., Conducting Polymer Nanocomposites: A Brief Overview. Chemistry

of Materials, 2000. 12: p. 608-622.12. Kang, E.T., K.G. Neoh, and K.L. Tan, Polyaniline: A polymer with many interesting intrinsic redox

states. Progress in Polymer Science, 1998. 23(2): p. 277-324.13. Shreepathi, S. and R. Holze, Spectroelectrochemical Investigations of Soluble Polyaniline

Synthesized via New Inverse Emulsion Pathway. Chemistry of Materials, 2005. 17(16): p. 4078-4085.

14. Harada, I., Y. Furukawa, and F. Ueda, Vibrational spectra and structure of polyaniline and relatedcompounds. Synthetic Metals, 1989. 29(1): p. 303-312.

15. Conroy, K.G. and C.B. Breslin, The electrochemical deposition of polyaniline at pure aluminium:electrochemical activity and corrosion protection properties. Electrochimica Acta, 2003. 48(6): p.721-732.

16. Olad, A. and B. Naseri, Preparation, characterization and anticorrosive properties of a novelpolyaniline/clinoptilolite nanocomposite. Progress in Organic Coatings, 2010. 67(3): p. 233-238.

17. Zhang, L., et al., Self-Assembled Hollow Polyaniline/Au Nanospheres Obtained by a One-StepSynthesis. Macromolecular Rapid Communications, 2008. 29(7): p. 598-603.

18. Zhang, L., M. Wan, and Y. Wei, Nanoscaled Polyaniline Fibers Prepared by Ferric Chloride as anOxidant. Macromolecular Rapid Communications, 2006. 27(5): p. 366-371.

19. Kinyanjui, J.M., et al., Chemical Synthesis of a Polyaniline/Gold Composite UsingTetrachloroaurate. Chemistry of Materials, 2004. 16(17): p. 3390-3398.

20. Pillalamarri, S.K., et al., One-Pot Synthesis of Polyaniline−Metal Nanocomposites. Chemistry ofMaterials, 2005. 17(24): p. 5941-5944.

21. Feng, X., et al., Self-Assembly of Polyaniline/Au Composites: From Nanotubes to Nanofibers.Macromolecular Rapid Communications, 2006. 27(1): p. 31-36.

89

22. Wang, Z., et al., One-step synthesis of gold–polyaniline core–shell particles. Nanotechnology,2007. 18(11): p. 115610.

23. Can, M., S. Uzun, and N.Ö. Pekmez, Chemical polymerization of aniline using periodic acid inacetonitrile. Synthetic Metals, 2009. 159(14): p. 1486-1490.

24. Du, D., et al., Acetylcholinesterase biosensor design based on carbon nanotube-encapsulatedpolypyrrole and polyaniline copolymer for amperometric detection of organophosphates.Biosensors and Bioelectronics, 2010. 25(11): p. 2503-2508.

25. Li, J., et al., Synthesis and thermoelectric properties of hydrochloric acid-doped polyaniline.Synthetic Metals, 2010. 160(11–12): p. 1153-1158.

26. Lijuan Zhang, et al., Polyaniline nanotubes doped with polymeric acids. Current Applied Physics,2008. 8: p. 312-315.

27. Nurxat Nuraje, et al., Liquid/Liquid Interfacial Polymerization To Grow Single CrystallineNanoneedles of Various Conducting Polymers. acs nano, 2008. 2: p. 502-506.

28. Gupta, K., et al., Temperature dependent dc and ac electrical transport properties of thecomposite of a polyaniline nanorod with copper chloride. Solid State Communications, 2011.151(7): p. 573-578.

29. Yang Li, et al., Water-soluble polyaniline and its composite with poly(vinyl alcohol) for humiditysensing. Synthetic Metals, 2010. 160: p. 455-461.

30. Gangopadhyay, R., A. De, and G. Ghosh, Polyaniline–poly(vinyl alcohol) conducting composite:material with easy processability and novel application potential. Synthetic Metals, 2001. 123(1):p. 21-31.

31. Heeger, A.J., Semiconducting and Metallic Polymers: The Fourth Generation of PolymericMaterials (Nobel Lecture). Angewandte Chemie International Edition, 2001. 40(14): p. 2591-2611.

32. Sathiyanarayanan, S., et al., Sulphonate doped polyaniline containing coatings for corrosionprotection of iron. Surface and Coatings Technology, 2010. 204(9–10): p. 1426-1431.

33. Zhang, Y., et al., High efficient removal of mercury from aqueous solution by polyaniline/humicacid nanocomposite. Journal of Hazardous Materials, 2010. 175(1–3): p. 404-409.

34. Naoi, K., et al., Application of electrochemically formed polypyrrole in lithium secondarybatteries: Analysis of anion diffusion process. Journal of Power Sources, 1987. 20(3–4): p. 237-242.

35. Green, A.G. and A.E. Woodhead, CCXLIII.-Aniline-black and allied compounds. Part I. Journal ofthe Chemical Society, Transactions, 1910. 97: p. 2388-2403.

36. Green, A.G. and A.E. Woodhead, CXVII.-Aniline-black and allied compounds. Part II. Journal ofthe Chemical Society, Transactions, 1912. 101: p. 1117-1123.

37. Spange, S., Electrochemical Synthesis of Novel Polyaniline-Montmorillonite Nanocomposites andCorrosion Protection of Steel.

38. Geniès, E.M., et al., Polyaniline: A historical survey. Synthetic Metals, 1990. 36(2): p. 139-182.39. J. Stejskal and R. G. Gilbert, Pure Appl. Chem 2002. 74: p. 857.40. P. S. Rao, D. N. Sathyanarayana, and T. Jeevananda, In Advanced Functional Molecules and

Polymers, H. S. Nalwa (ed.), Gordon and Breach, Tokyo,, 2001. Vol. 3: p. 79.41. Li, D., J. Huang, and R.B. Kaner, Polyaniline Nanofibers: A Unique Polymer Nanostructure for

Versatile Applications. Accounts of Chemical Research, 2008. 42(1): p. 135-145.42. Brazovskii, S. and N. Kirova, Excitons, polarons, and bipolarons in conducting polymers. Jetp Lett,

1981. 33(1): p. 4.43. Wnek, G.E., A proposal for the mechanism of conduction in polyaniline. Synthetic Metals, 1986.

15(2–3): p. 213-218.

90

44. Lundberg, B., W.R. Salaneck, and I. Lundström, Pressure, temperature and field dependence ofhopping conduction in polyaniline. Synthetic Metals, 1987. 21(1–3): p. 143-147.

45. Holze, R., In Advanced Functional Molecules and Polymers, H. S. Nalwa (ed.), Gordon andBreach, Tokyo,, 2001. vol.2: p. 171.

46. Shim, Y.-B. and S.-M. Park, Electrochemistry of conductive polymers VII. Autocatalytic rateconstant for polyaniline growth. Synthetic Metals, 1989. 29(1): p. 169-174.

47. Mohilner, D.M., R.N. Adams, and W.J. Argersinger, Investigation of the Kinetics and Mechanismof the Anodic Oxidation of Aniline in Aqueous Sulfuric Acid Solution at a Platinum Electrode.Journal of the American Chemical Society, 1962. 84(19): p. 3618-3622.

48. Yang, H. and A.J. Bard, The application of fast scan cyclic voltammetry. Mechanistic study of theinitial stage of electropolymerization of aniline in aqueous solutions. Journal of ElectroanalyticalChemistry, 1992. 339(1–2): p. 423-449.

49. Chiang, J.-C. and A.G. MacDiarmid, ‘Polyaniline’: Protonic acid doping of the emeraldine form tothe metallic regime. Synthetic Metals, 1986. 13(1–3): p. 193-205.

50. A. J. Heeger and Angew, Chem. Int. Ed., 2001. 40: p. 2591.51. Murugesan, R. and E. Subramanian, The effect of Cu(II) coordination on the structure and electric

properties of polyaniline–poly(vinyl alcohol) blend. Materials Chemistry and Physics, 2003. 77(3):p. 860-867.

52. Izumi, C.M.S., et al., Spectroscopic characterization of polyaniline doped with transition metalsalts. Synthetic Metals, 2006. 156(9-10): p. 654-663.

53. Aoki, K., et al., Redox Reactions of Polyaniline-Coated Latex Suspensions. Langmuir, 2003. 19(13):p. 5511-5516.

54. Marie, E., et al., Synthesis of Polyaniline Particles via Inverse and Direct Miniemulsion.Macromolecules, 2003. 36(11): p. 3967-3973.

55. Nguyen, M.T., et al., Synthesis and Properties of Novel Water-Soluble Conducting PolyanilineCopolymers. Macromolecules, 1994. 27(13): p. 3625-3631.

56. Wessling, B., Polyaniline on the metallic side of the insulator-to-metal transition due todispersion: the basis for successful nano-technology and industrial applications of organicmetals. Synthetic Metals, 1999. 102(1–3): p. 1396-1399.

57. Bilal, S., et al., Synthesis and characterization of completely soluble and highly thermally stablePANI-DBSA salts. Synthetic Metals, 2012. 162(24): p. 2259-2266.

58. Xu, L.G., S.C. Ng, and H.S.O. Chan, Polyaniline with ω-hydroxyalkoxy pendant substituent on themeta-position. Synthetic Metals, 2001. 123(3): p. 403-410.

59. Dhawan, S.K. and D.C. Trivedi, Influence of polymerization conditions on the properties of poly(2-methylaniline) and its copolymer with aniline. Synthetic Metals, 1993. 60(1): p. 63-66.

60. Lin, H.-K. and S.-A. Chen, Synthesis of New Water-Soluble Self-Doped Polyaniline.Macromolecules, 2000. 33(22): p. 8117-8118.

61. Chan, H.S.O., et al., A New Water-Soluble, Self-Doping Conducting Polyaniline from Poly(o-aminobenzylphosphonic acid) and Its Sodium Salts: Synthesis and Characterization. Journal ofthe American Chemical Society, 1995. 117(33): p. 8517-8523.

62. Anjum, M.N., et al., Tailoring of chiroptical properties of substituted polyanilines by controllingsteric hindrance. Polymer, 2011. 52(25): p. 5795-5802.

63. Probst, M. and R. Holze, A systematic spectroelectrochemical investigation of alkyl-substitutedanilines and their polymers. Macromolecular Chemistry and Physics, 1997. 198(5): p. 1499-1509.

64. Schemid, A.L., L.M. Lira, and S.I. Córdoba de Torresi, On the electrochemical and spectroscopicproperties of a soluble polyaniline parent copolymer. Electrochimica Acta, 2002. 47(12): p. 2005-2011.

91

65. Wei, Y., R. Hariharan, and S.A. Patel, Chemical and electrochemical copolymerization of anilinewith alkyl ring-substituted anilines. Macromolecules, 1990. 23(3): p. 758-764.

66. Han, C.-C., et al., Highly Conductive New Aniline Copolymers Containing Butylthio Substituent.Macromolecules, 2000. 34(3): p. 587-591.

67. Savitha, P., P. Swapna Rao, and D.N. Sathyanarayana, Highly conductive new aniline copolymers:poly(aniline-co-aminoacetophenone)s. Polymer International, 2005. 54(9): p. 1243-1250.

68. Huber, C., et al., Microengineered conducting composites from nanochannel templates.Advanced Materials, 1995. 7(3): p. 316-318.

69. Anand, J., S. Palaniappan, and D.N. Sathyanarayana, Conducting polyaniline blends andcomposites. Progress in Polymer Science, 1998. 23(6): p. 993-1018.

70. Yang, S. and E. Ruckenstein, Preparation and mechanical properties of electrically conductivepolypyrrole-poly(ethylene-co-vinyl acetate) composites. Synthetic Metals, 1993. 60(3): p. 249-254.

71. Banerjee, P. and B.M. Mandal, Conducting Polyaniline Nanoparticle Blends with Extremely LowPercolation Thresholds. Macromolecules, 1995. 28(11): p. 3940-3943.

72. Swapna, P., R.S. Subrahmanya, and D.N. Sathyanarayana, Water-soluble conductive blends ofpolyaniline and poly(vinyl alcohol) synthesized by two emulsion pathways. Journal of AppliedPolymer Science, 2005. 98(2): p. 583-590.

73. Jousseaume, V., et al., X-ray photoelectron spectroscopy of conducting polyaniline andpolyaniline–polystyrene blends. Journal of Applied Polymer Science, 1998. 67(7): p. 1209-1214.

74. Im, S.S. and S.W. Byun, Preparation and properties of transparent and conducting nylon 6-basedcomposite films. Journal of Applied Polymer Science, 1994. 51(7): p. 1221-1229.

75. Kuramoto, N. and E.M. Geniès, Micellar chemical polymerization of aniline. Synthetic Metals,1995. 68(2): p. 191-194.

76. Kuramoto, N. and A. Tomita, Aqueous polyaniline suspensions: Chemical oxidativepolymerization of dodecylbenzene-sulfonic acid aniline salt. Polymer, 1997. 38(12): p. 3055-3058.

77. Kim, B.-J., et al., Synthesis and characterization of polyaniline nanoparticles in SDS micellarsolutions. Synthetic Metals, 2001. 122(2): p. 297-304.

78. Yu, L., et al., Preparation of aqueous polyaniline dispersions by micellar-aided polymerization.Journal of Applied Polymer Science, 2003. 88(6): p. 1550-1555.

79. Hassan, P.A., et al., Polyaniline Nanoparticles Prepared in Rodlike Micelles. Langmuir, 2004.20(12): p. 4874-4880.

80. Dodouche, I. and F. Epron, Promoting effect of electroactive polymer supports on the catalyticperformances of palladium-based catalysts for nitrite reduction in water. Applied Catalysis B:Environmental, 2007. 76(3–4): p. 291-299.

81. Stejskal, J., et al., The reduction of silver nitrate with various polyaniline salts to polyaniline–silvercomposites. Reactive and Functional Polymers, 2009. 69(2): p. 86-90.

82. Gupta, K., P.C. Jana, and A.K. Meikap, Electrical transport and optical properties of the compositeof polyaniline nanorod with gold. Solid State Sciences, 2012. 14(3): p. 324-329.

83. Ćirić-Marjanović, G., Recent advances in polyaniline composites with metals, metalloids andnonmetals. Synthetic Metals, 2013. 170(0): p. 31-56.

84. Mallick, K., et al., Polymerization of Aniline by Cupric Sulfate: A Facile Synthetic Route forProducing Polyaniline. Journal of Polymer Research, 2006. 13(5): p. 397-401.

85. Li, X., et al., Polyaniline/CuCl nanocomposites prepared by UV rays irradiation. Materials Letters,2008. 62(15): p. 2237-2240.

86. Chen, Z., et al., A green route to conducting polyaniline by copper catalysis. Journal of Catalysis,2009. 267(2): p. 93-96.

92

87. Le Cocq, A., et al., Reactions of Aniline with Copper(ii) Compounds in Relation to the Formationof Copper-Polyaniline Composites*. Australian Journal of Chemistry, 2012: p. -.

88. Lundström, M., J. Aromaa, and O. Forsén, Redox potential characteristics of cupric chloridesolutions. Hydrometallurgy, 2009. 95(3–4): p. 285-289.

89. Bian, C. and A. Yu, De-doped polyaniline nanofibres with micropores for high-rate aqueouselectrochemical capacitor. Synthetic Metals, 2010. 160(13–14): p. 1579-1583.

90. Zeng, X.-R. and T.-M. Ko, Structures and properties of chemically reduced polyanilines. Polymer,1998. 39(5): p. 1187-1195.

91. Stejskal, J., P. Kratochvil, and M. Špírková, Accelerating effect of some cation radicals on thepolymerization of aniline. Polymer, 1995. 36(21): p. 4135-4140.

92. Laska, J. and J. Widlarz, Spectroscopic and structural characterization of low molecular weightfractions of polyaniline. Polymer, 2005. 46(5): p. 1485-1495.

93. Chandrakanthi, R.L.N. and M.A. Careem, Preparation and characterization of CdS and Cu2Snanoparticle/polyaniline composite films. Thin Solid Films, 2002. 417(1–2): p. 51-56.

94. Albuquerque, J.E., et al., A simple method to estimate the oxidation state of polyanilines.Synthetic Metals, 2000. 113(1–2): p. 19-22.

95. Kang, E.T., et al., Protonation and deprotonation of polyaniline films and powders: effects of acidand base concentrations on the surface intrinsic oxidation states. Synthetic Metals, 1998. 92(2):p. 167-171.

96. do Nascimento, G.M., et al., Aniline Polymerization into Montmorillonite Clay: A SpectroscopicInvestigation of the Intercalated Conducting Polymer. Macromolecules, 2004. 37(25): p. 9373-9385.

97. Magnuson, M., et al., The electronic structure of polyaniline and doped phases studied by soft X-ray absorption and emission spectroscopies. Journal Name: Journal of Chemical Physics; JournalVolume: 111; Journal Issue: 10; Other Information: Journal Publication Date: September 1999;PBD: 1 Sep 1999, 1999: p. Medium: X; Size: vp.

98. Gizdavic-Nikolaidis, M. and G.A. Bowmaker, Iodine vapour doped polyaniline. Polymer, 2008.49(13–14): p. 3070-3075.

99. Hagiwara, T., M. Yamaura, and K. Iwata, Structural analysis of deprotonated polyaniline by solid-state 13C N.M.R. Synthetic Metals, 1988. 26(2): p. 195-201.

100. Kaplan, S., et al., Solid-state carbon-13 NMR characterization of polyanilines. Journal of theAmerican Chemical Society, 1988. 110(23): p. 7647-7651.

101. Sahoo, S.K., et al., An Enzymatically Synthesized Polyaniline: A Solid-State NMR Study.Macromolecules, 2004. 37(11): p. 4130-4138.

102. Ding, H., M. Wan, and Y. Wei, Controlling the Diameter of Polyaniline Nanofibers by Adjustingthe Oxidant Redox Potential. Advanced Materials, 2007. 19(3): p. 465-469.

103. Patil, D.S., et al., Chemical synthesis of highly stable PVA/PANI films for supercapacitorapplication. Materials Chemistry and Physics, 2011. 128(3): p. 449-455.

104. Izumi, C.M.S., et al., Spectroscopic characterization of polyaniline doped with transition metalsalts. Synthetic Metals, 2006. 156(9–10): p. 654-663.

105. Chowdhury, A.-N., M.S. Islam, and M.S. Azam, Polyaniline matrix containing nickel ferromagnet.Journal of Applied Polymer Science, 2007. 103(1): p. 321-327.

106. Dimitriev, O.P., Doping of Polyaniline by Transition-Metal Salts. Macromolecules, 2004. 37(9): p.3388-3395.

107. Karim, M.R., et al., Conducting polyaniline-titanium dioxide nanocomposites prepared byinverted emulsion polymerization. Polymer Composites, 2010. 31(1): p. 83-88.

108. Gizdavic-Nikolaidis, M., et al., Spectroscopic studies of interactions of polyaniline with someCu(II) compounds. Current Applied Physics, 2006. 6(3): p. 457-461.

93

109. Palaniappan, S. and B.H. Narayana, Temperature effect on conducting polyaniline salts: Thermaland spectral studies. Journal of Polymer Science Part A: Polymer Chemistry, 1994. 32(13): p.2431-2436.

110. Gemeay, A.H., et al., Preparation and characterization of polyaniline/manganese dioxidecomposites via oxidative polymerization: Effect of acids. European Polymer Journal, 2005.41(11): p. 2575-2583.

111. Özdemir, U., et al., Modeling adsorption of sodium dodecyl benzene sulfonate (SDBS) ontopolyaniline (PANI) by using multi linear regression and artificial neural networks. ChemicalEngineering Journal, 2011. 178(0): p. 183-190.

112. Pournaghi-Azar, M.H. and B. Habibi, Electropolymerization of aniline in acid media on the bareand chemically pre-treated aluminum electrodes. Electrochimica Acta, 2007. 52(12): p. 4222-4230.

113. Bilal, S. and R. Holze, Electrochemical copolymerization of o-toluidine and o-phenylenediamine.Journal of Electroanalytical Chemistry, 2006. 592(1): p. 1-13.

114. Trung, T., T.H. Trung, and C.-S. Ha, Preparation and cyclic voltammetry studies on nickel-nanoclusters containing polyaniline composites having layer-by-layer structures. ElectrochimicaActa, 2005. 51(5): p. 984-990.

115. Scully, M., M.C. Petty, and A.P. Monkman, Optical properties of polyaniline thin films. SyntheticMetals, 1993. 55(1): p. 183-187.

116. Malinauskas, A. and R. Holze, In situ UV–VIS spectroelectrochemical study of polyanilinedegradation. Journal of Applied Polymer Science, 1999. 73(2): p. 287-294.

117. Stilwell, D.E. and S.M. Park, Electrochemistry of Conductive Polymers V. In SituSpectroelectrochemical Studies of Polyaniline Films. Journal of The Electrochemical Society,1989. 136(2): p. 427-433.

118. Leclerc, M., Characterization of a bipolaronic form in poly(2-methylaniline). Journal ofElectroanalytical Chemistry and Interfacial Electrochemistry, 1990. 296(1): p. 93-100.

119. D'Aprano, G., M. Leclerc, and G. Zotti, Steric and electronic effects in methyl and methoxysubstituted polyanilines. Journal of Electroanalytical Chemistry, 1993. 351(1–2): p. 145-158.

120. Shi, Z., et al., Photoinduced protonation of polyaniline assisted by hydrogen-bonding materials.Synthetic Metals, 2011. 161(13–14): p. 1420-1423.

121. Bhadra, S., et al., Improvement of conductivity of electrochemically synthesized polyaniline.Journal of Applied Polymer Science, 2008. 108(1): p. 57-64.

122. Bhadra, J. and D. Sarkar, Size variation of polyaniline nanoparticles dispersed in polyvinyl alcoholmatrix. Bulletin of Materials Science, 2010. 33(5): p. 519-523.

123. Honmute, S., et al., Studies on Polyaniline-Polyvinyl Alcohol (PANI-PVA) Interpenetrating PolymerNetwork (IPN) Thin Films. International Journal of Science Research, 2012. 1(2): p. 102-106.

124. Misra, N., et al., Polyaniline-poly(vinyl alcohol) IPN-composite prepared from potassiumdichromate embedded PVA film: a material for humidity sensing application. Indian Journal ofPhysics, 2011. 85(5): p. 703-712.

125. Rao, P.S., et al., Effect of sulphuric acid on the properties of polyaniline–HCl salt and its base.European Polymer Journal, 2000. 36(5): p. 915-921.

126. Swaruparani, H., et al., A new approach to soluble polyaniline and its copolymers with toluidines.Journal of Applied Polymer Science, 2010. 117(3): p. 1350-1360.

127. Bedre, M.D., et al., Preparation and characterization of Pani and Pani-Ag nanocomposites viainterfacial polymerization. Polymer Composites, 2009. 30(11): p. 1668-1677.

128. Shahi, M., et al., Electrospun PVA–PANI and PVA–PANI– composite nanofibers. Scientia Iranica,2011. 18(6): p. 1327-1331.

94

129. Adhikari, S. and P. Banerji, Polyaniline composite by in situ polymerization on a swollen PVA gel.Synthetic Metals, 2009. 159(23–24): p. 2519-2524.

130. Mirmohseni, A. and G.G. Wallace, Preparation and characterization of processable electroactivepolyaniline–polyvinyl alcohol composite. Polymer, 2003. 44(12): p. 3523-3528.

131. Sindhu honmute, A.l., A. Venkataraman, Synthesis and Characterisation of Polyaniline-PolyvinylAlcohol-NiO Nanocomposite Film. Indian Journal of Applied Research, 2013. 3(8): p. 91-93.

132. Divya, V. and M.V. Sangaranarayanan, A facile synthetic strategy for mesoporous crystallinecopper–polyaniline composite. European Polymer Journal, 2012. 48(3): p. 560-568.

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