Pushkar N Patil

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Nanoscale free volume hole distribution and its correlation with physico- chemical properties of polymers Pushkar N. Patil Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085

Transcript of Pushkar N Patil

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Nanoscale free volume hole distribution and its correlation with physico-chemical properties of polymers

Pushkar N. Patil

Radiochemistry Division,Bhabha Atomic Research Centre,

Trombay, Mumbai 400 085

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Polymeric system: Study of synthetic polymers has received enormous attention due to their wideapplications in the various fields

Utility of the polymer for desirable purpose depends on their physical and chemicalproperties

Designing the polymeric system for specific application is always a challenging task

Free volume is one of the important factors that explains the degree of segmental andterminal relaxation of the polymeric chains which ultimately affects thermo-mechanicalproperties.

Synthesis of few industrial polymeric systems in various methods is carried out tomodify free volume holes and its related physico-chemical properties

Positron: Positron Annihilation Spectroscopy is an established technique to measure the freevolumes

Positrons have propensity to get localized at low electron density region like defects inmetallic systems and free volume nanoholes in polymers.

Introduction

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P. A. M. Dirac (1928) predicted the existence of a positron in

C. D. Anderson (1933) observed the positrons in cloud chamber

• Positron is an antiparticle of electron• Same mass as that of electron (rest mass = 511keV)• Opposite in their charges and their attendant properties

P. A. M. Dirac

C. D. Anderson

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Positron in Polymeric medium

Step-1: Thermalization

Step-2:Free positron annihilation OR Positronium (Ps) formation

Para-Positronium Ortho-PositroniumNotation p-Ps o-PsIntrinsic lifetime 0.125 ns 142 nsMode of annihilation 2 (of 511keV) 3 (0-511 keV)Spin state (Anti-parallel) (parallel)Fraction of formation 1/4 3/4

Positron loses its kinetic energy in the sample due to the inelastic collision,(10-12 ps)

e+e-

511 keV

Ps 511 keV

Lifetime reduces from 142 ns to 1- 10 ns

Step-3: Ps “Pick-off” annihilation

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Experimental TechniquesPositron annihilation Spectroscopy

Positron Source : 22Na

(i) Positron annihilation lifetime spectroscopy (PALS)(free volume size, concentration and their distribution)

(ii) Doppler broadening spectroscopy (DBS)(defect/free volume and electron momentum)

(iii) Age momentum correlation (AMOC) spectroscopy(electron momentum at different positron age)

Slow positron beam

(i) Depth dependent defect studies (DBS)

Supplementary techniques: XRD, DMA, mDSC

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Positron annihilation lifetime spectrometerWe measure the time difference between the birth (1275 keVprompt gamma) and death of a positron/Positronium (511 keVgamma) using a fast-fast coincidence circuitry.

1( ) ( ) * i

tki

i i

IF t R e B

200 400 600 800 1000 120010

100

1000

10000

Cou

nts

Channels

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Doppler broadening spectrometerMeasurement of 511 keV gamma line (which undergoes line width broadening) using high resolution Gamma-ray spectroscopy

2Zp CE

Doppler broadening of annihilationgamma line proportional to electron kinetic energy

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Age momentum correlation (AMOC) spectrometerAMOC involves the correlated measurement between positronlifetime and electron momentum distribution from the sameannihilation event. It can differentiate the positron states indifferent media.

BaF2STOP

BaF2START

High Voltage

High Voltage

High Voltage

HPGe det.

Spec. Amplifier

TFA TSCA

CFDD

GDG

GDG

CFDD Delay Delay Amp.TAC

Universal C

oincidence Unit

Linear Gate and Stretcher / G

DG

Multiparam

eter data acquisition system

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Nanoscale free volumes in Polymer

Free-volume influences,

1) mechanical properties (viscoelastisic nature)2) transport properties (diffusion of liquid/gas molecules)3) phase transition (Tg and sub Tg)

Excluded volumeFree-volume

Positronium (Ps) is sensitive to free volumes Ps life time gives the information about free volume size, concentration and their distribution

• due to the segmental and terminal motion of molecular chains

1 1 2( ) 2 1 sin2

R RnsR R R R

The Tao-Eldrup equation

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Molecular packing and swelling properties of polymer hydrogels

Structure-property relationships in modified epoxy resins

Free volume nanoholes and interfacial interaction in Epoxy/modified clay composites

Bulk and surface studies in Ag nanoparticles incorporated Nafion membrane

Objectives

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Influence of free volume properties of poly (N-isopropyl acrylamide) on their swelling in water

Hydrogel, potential uses in biomedical applications, drug delivery systems, separation sciences etc.

N-isopropyl acrylamide (NIPA), a thermo-responsive hydrogel with lower critical solution temperature (LCST) of about 32˚C

But, still a swelling study of the hydrogels is debatable

Many attempts have been made to improve the swelling kinetics of these gels by altering the preparation procedures and introducing other copolymers into the gel network

Therefore, in this study, the effect of the chemical nature of crosslinkers and synthesis solvent in the swelling properties of these gels has been studied in the context of their free volume properties

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two different synthesis solvents,

1) Dimethyl formamide (DMF), aprotic solvent 2) Methanol (MeOH), protic solvent

All Hydrogel samples were prepared by U.V. polymerization using α,α-dimethoxy-α-phenylacetophenone as a photo initiator

Chemical structures of the crosslinkers

CC

C

C

C

C

C

C

C

C

C

C

C

C

C

O

OO

O

O

O

O

H2

H2

H2H2

H2

H2

H2

H

H

H

O

CC

H2

H

Ethylene Glycol Dimethacrylate (EGDM), tetrafunctional, straight chain

Penta erythritol Tetraacrylate (PETA), octafunctional, branched

1,4 – Butanediol diacrylate (1,4 B), Short chain

1,6 – Hexanediol diacrylate (1,6 H), Long chain

CHCH2

C O

NHCH(CH3)2

N-isopropyl acrylamide

CH2OC

C

O

O

H2CC

CO

H

H

CH2OC

C

O

O

H2CC

CO

H

H

CH2OC

C

O

O

H2CC

CO

CH3

CH3

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2 3 4 5 6 7 8 9 10 110

100

200

300

400

500

Perc

enta

ge E

quili

brum

Sw

ellin

g

mole % of cross linker

EGDM-MeOH EGDM-DMF

2 3 4 5 6 7 8 9 10 110

50

100

150

200

250

300

350

400

mole % of cross linker

Perc

enta

ge E

quili

brum

Sw

ellin

g PETA-MeOH PETA-DMF

Effect of synthesis solvent on Swelling

The percentage equilibrium swelling (PES) at room temperature in deionizedwater

PES = 100w d

d

W WW

where, Ww is the weight of the swollen gel

Wd is the weight of dry gel

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2 3 4 5 6 7 8 9 10 111.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

mole % of cross linker

Frac

tiona

l fre

e vo

lum

e (r

elat

ive)

EGDM-MeOH EGDM-DMF

2 3 4 5 6 7 8 9 101.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Frac

tiona

l fre

e vo

lum

e (r

elat

ive)

mole % of cross linker

PETA-MeOH PETA-DMF

fractional free volume can’t explain the effect of solvent

Fractional free volume

fv=c(4/3ΠR3)I3

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2 3 4 5 6 7 8 9 10 1118

19

20

21

22

23

24

25

26 EGDM-MeOH EGDM-DMF

wid

th o

f rad

ius d

istri

butio

n (R

elat

ive)

mole % of cross linker 2 3 4 5 6 7 8 9 10 11

18

20

22

24

26

28

30

32

mole % of cross linker

wid

th o

f rad

ius d

istri

butio

n (R

elat

ive)

PETA-MeOH PETA-DMF

Relative width of free volume radius distribution

nicely explains the experimental results

MeOH is less polar and Protic solventDMF is more polar and Aprotic solvent

Swelling is facilitated by not the free volume fraction but, the free volume hole size distribution

Polym. Bull., 65 (2010), 577-581

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Neil Graham in 1998, indicated the microgelation and macrogelation formation duringthe polymerization.

the solubility parameter is the fundamental thermodynamic property for polymers and isused extensively for the discussion of the miscibility of the polymers in the solvents.

The solubility parameter for the NIPA gel is 11.2 (cal/cm3)1/2 whereas, the solubilityparameters for the DMF and methanol are 12.1 and 14.5 (cal/cm3)1/2, respectively

DMF leads to homogenous crosslinking with well defined microstructure

Methanol leads to inhomogeneous crosslinking results into the cluster formation

Mater. Sci. Forum, 733 (2013), 155-158

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Influence of free volumes on the thermo-mechanical properties in epoxy resin

Epoxy resins are considered as model systems to study the relaxation phenomena. Therelaxation behavior is profoundly influenced by the chemical structure of the polymers.

A series of epoxy-poly ether diamine networks has been prepared with systematicvariation in the degree of crosslinking.

Chemical structures of epoxy resins and diamines:

characteristic length of glass transitions is evaluated using modulated DSC (MDSC).

viscoelastic parameters and crosslink density are evaluated from DMA

Molecular topology of the networks is determined by PALS

Glassy Rubbery

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Characteristic length of glass transition from MDSC

Glass transition, Tg and length scale of cooperativity, ξ(Tg) are evaluated using the derivative of reversing heat capacity (Cp) signals.

ξ(Tg) has calculated from Donth thermal fluctuation theory -

3/1

2

2

)()/1(

TCkT V

EPD-230

EPED-900

Reversible Cp and its derivative for EPD-230 (glassy) and EPED-900 (rubbery) networks are shown in figures,

Sample ID (g/cm3) Tg (K) (1/Cp) δT (K) (nm)

Pure epoxy 1.140 257 0.2812 2.33 3.42

EPD-230 1.174 361 0.0338 2.55 2.00

EPD-400 1.154 320 0.050 2.62 2.07

EPED-600 1.169 291 0.0325 2.87 1.58

EPED-900 1.163 265 0.0456 3.69 1.41

Thermal fluctuation parameters at Tg :

Rubbery networks require smaller cooperative volume for Tg

Dependence of the ξ(Tg) on chemical nature of diamines

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α relaxation characteristics α relaxation phenomenon is attributed to the glass transition (Tg)

storage modulus, E′ vs. T and tanδ vs. T have been measured for all epoxy networks.

In each case E' drops sharply in the high temperature range where the dissipation factor (tan δ) displays a maximum.

α relaxation peak is single and well defined (absence of any phase separation)

low temperature tan δ peak characterizes the subglassy relaxation process (β relaxation)

Two relaxation zones for all the epoxy networks are present in both the plots.

crankshaft motion of the hydroxyl ether groups in epoxy-amine networks

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various parameters of the α relaxation

α relaxation temperature (Tg) increases with increasing crosslink density.

These effects are consistent with the decreased intensity of the rotational andtranslational modes of molecular motion with increasing crosslink density and hence thedecreased length of the interjection distances

Consequently, the value of E' (at Tg+ 30 K) decreases with decreased crosslink density(enhanced molecular mobility)

Sample ID α relaxation

temperature

(Tg) (K)

tan δ

(peak intensity)

Width

(K)

Storage modulus,

E′(MPa) at

Tg + 30K

Crosslink

density,

(ν x103 )

(moles/m3)

EPD-230 369.0 1.08 9.50 17.2 1.90

EPD-400 336.0 1.35 9.63 10.6 1.26

EPED-600 296.8 1.58 12.50 8.9 1.20

EPED-900 275.1 1.28 14.81 6.1 0.89

The crosslink density (υ) of the epoxy-amine networks was evaluated from E' vs. T plots at Tg + 30 K, using

υ = E'/3RT, where R is the gas constant and T is the absolute temperature

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β relaxation characteristics occurrence of a clearly well defined β transition is seen for all the networks, inagreement with the reported results

Glassy (EPD-230 and EPD-400 ) networks, similar relaxation characteristics

Rubbery (EPED-600 and EPED-900), markedly different relaxation pattern

β transition Glassy Epoxy Rubbery Epoxy

width Broad Narrow

amplitude Lower Higher

Temperature at Higher Lower

characteristics of the β transitions used for quantitative treatment of sub-glassy process:

Sample ID β maxima

(K)

Relaxation

Intensity

Width

(K)

Ea,max

(kJmol-1)

EPD-230 217.61 130.43 69.76 72.5

EPD-400 208.68 74.61 50.31 66.3

EPED-600 198.80 64.85 37.26 54.8

EPED-900 193.78 129.6 26.42 -

lower crosslink densitynetworks (EPED 600and 900),regarded as internallyplasticized systems dueto the presence offlexible POE blocks.

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to gain further understanding of the β relaxation process, the activation energy wascalculated from frequency dependence of the relaxation process

E" vs. temperature plot of the model epoxy networks as a function of frequency

)/exp( RTEAf a The activation energy depends on both the intramolecular contributions (internalrotation barriers) and intermolecular components (environment of the relaxing units).

the peak maxima shifts towards high temperature and the intensity of the peakincreases with increasing frequency.

with decreasing crosslink density, the Ea,max of the epoxy-amine networks decreases.

thermally activated relaxation frequencies represent an Arrhenius type expression

Arrhenius plot for EPD-230 sample

Slope = Ea,max.= 72.5kJ/mole

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Sample ID o-Ps lifetime

τ3 (ns)

o-Ps Intensity

I3 (%)

Free volume

radius R (nm)

Fractional free

volume fv

EPD-230 1.61 ± 0.01 19.45 ± 0.20 0.246 2.18

EPD-400 1.69 ± 0.01 20.25 ± 0.19 0.255 2.53

EPED-600 1.81 ± 0.01 18.79 ± 0.17 0.267 2.69

EPED-900 1.95 ± 0.01 21.00 ± 0.14 0.281 3.51

The free volume parameters of the networks obtained from PALS

two classes of the networks (similar to MDSC and DMA results)

For the same kind of networks, both τ3 and I3 increase with decreasing crosslink density of the networks, as expected. Free volume hole size distribution and its parameters for all epoxy networks

The glassy networks show relatively lower values of free volume radius (R), volume υh, dispersionσ (υh) compared to the rubbery networks.

Free volume analysis

Sample ID Centroid

(υh) (nm3)

Dispersion

σ (υh) (nm3)

EPD-230 0.062 0.045

EPD-400 0.073 0.050

EPED-600 0.083 0.057

EPED-900 0.095 0.069

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Further, we calculated the mean distance between crosslinks (l), where the intrinsic holevolume elements can be localized to interpret the free volume data as 2R (diameter offree volume)

Theoretical ‘l’ values:3/1 dXl where, Xd is the theoretically calculated crosslink density and can be calculated by,

avd NMbMaX 2211 /)2(/)2(

The experimental l values were calculated from the DMA results by using the followingequation

s

As M

N

32

νs is the effective crosslink density of network sites, ρ is the density of the networks, NA is the Avogadro number and Ms = ρ/υ, where υ is the crosslink density values obtained from DMA

Experimental ‘l’ values:

Dependence of the mean distance between crosslinks (l), (l-2R) of the networks.

Sample ID l, theoretical (nm) l, experimental (nm) l-2R (nm)

Theor. Expt.

EPD-230 0.75 1.09 0.26 0.59

EPD-400 0.82 1.25 0.31 0.74

EPED-600 0.88 1.28 0.35 0.53

EPED-900 0.97 1.35 0.41 0.78

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can assume only the sub-glassy β relaxation time scales.

The β relaxation time τβ is known to have Arrhenius temperature dependence

)/exp( RTE

where τβ∞ is of the order of 10-13-10-16 s [Johari et al., 1970; 1971]. τβ∞ value of 10-14 s is used for thecalculation of τβ.Eβ is an activation energy of β relaxation obtained from DMA.

Thus, it can be emphasized that the time scale of relaxation associated with the sub-glassy β relaxation process has a bearing on the mean size of the free volume holes of glassy epoxy networks.

Whereas, the rubbery networks, does not follow this relation due to the danglingchains in the networks, leading to higher l values.

Is time scale of relaxation of the networks commensurate with the o-Ps lifetime of1.61 - 1.95 ns ?

From the results it is evident that the τβ (298 K) values are slower than the mean o-Pslifetimes of the networks, i.e. 4.7Χ10-2 s for EPD-230 and 3.9 Χ 10-3 s for EPD-400

Soft Matter, 9 (2013), 3589-3599

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Investigation of the microstructure in the epoxy\clay composite system

In recent years, polymer nanocomposite have attracted a great attention owing to theirunexpected hybrid properties that are synergistically derived from multicomponent.

Epoxy/clay nanocomposites were synthesized using modified clay to investigate thefree volume properties and interfacial interactions.

Clay was modified with the organic modifier,

Nanocomposites have been prepared with different weight % of clay i.e. 1, 3, 5, 7.5.

Clay dispersion has been studied using XRD and SEM

Free volume properties and Positron/Positronium states were examined by PAS

C H 2 C H 3N +

C H 3

H TH T - H ydrogenated T allow

(65% C 18; 30% C 16; 5% C 14)

C loisite 10A

Chem Phys Chem, 13 (2012), 3916-3922

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strong intercalation of epoxy matrix in between two consecutive silicate layers

no characteristic diffraction peak in EPJ1 (clay exfoliated morphology)

smooth fractured surface of the EPJ1 in SEM scan

diffraction peaks appear in EPJ3, 5 and 7.5 samples (clay intercalated morphology)

deformed regions resulting from the coarseness of the fractured surface in SEM scans

Characterization of nanocomposites

EPJ1

EPJ7.5EPJ5

EPJ3

2θ = 4.69°

d = 1.92nm

2θ = 2.68°

d = 3.29nm

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Free volume and interfacial properties

nanocomposites have lower fv as compared to pristine epoxy

fv decreases with clay loading upto 3 wt. % and saturates at higher concentration

Simple law of mixing - reduction in fv (exp) is more than fv (calc) – interfacial interaction

the deviation between experimental and calculated I2 values is maximum for EPJ1sample and further reduces with increase in clay concentration

exfoliated morphology in EPJ1 sample enhances the interfacial interaction while theclay agglomeration at higher clay concentration reduces the interfacial interaction aswell as the fractional free volumes

● experimental

○ calculated

● experimental

○ calculated

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AMOC measurements

S(t) parameter profilefor pristine epoxy iswell consistent with thereported literature

Low average S-parameter valuein pure clay →crystalline nature

same chemical environment trapping of positron atinterfacial layer

positrons trapped andannihilate from clayagglomerate and notfrom the epoxy/clayinterface

Clay concentration

Clay morphology fv Free positron trapping and

annihilation from

Interfacial interaction

(I2)Low Exfoliated High Interfacial layer Strong

High Intercalated Low Clay agglomerates Weak

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1.60

40( ) ( )Z E E

Implantation depth of positron depends upon positron energy and polymer density,

Surface analysis: depth dependent measurementsSlow Positron Beam Setup at Radiochemistry Division, BARC.

• In present case, the surface morphology (about 2 μm) is studied using the positronenergy range of 0.2 to 15 keV

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0 2 4 6 8 10 12 14

0.455

0.460

0.465

0.470

0.475

0.480

0.485

0.490

2.3721.8541.3840.9690.6110.3190.1050.000

Mean Implantation Depth (m)

Positron energy (keV)

S-pa

ram

eter

EPJ0 EPJ1 EPJ3

VEPFIT analysis

d t t bd c dD v c I z k n c cdz dz

2

2 ( ) 0 ,

Time averaged positron density c(z) is given by the following equation

Where, c(z) = the time averaged positron density,vd(z) = E(z) = the drift velocity with positron mobility and electric field E,I(z) = positron trapping rate at depth z,nt(z)= the defect density,kt = rate constant for positron trapping at defects,b = bulk annihilation rate andD+ = positron diffusion coefficient

The general solution for vd=0 in the ith interval

ii i i i i

i

pc z A z B z( ) exp( ) exp( ) ,

i i ii t t bi

DLL k n

2 1/ 2,

, ,

1 , [ ]( )

L+ is the positron diffusion length in ith layer

0 2 4 6 8 10 12 14

0.455

0.460

0.465

0.470

0.475

0.480

0.485

0.4902.3720.9690.3190.105 1.8541.3840.6110.000

EPJ0 EPJ5 EPJ7.5

Positron energy (keV)

S-pa

ram

eter

Mean Implantation Depth (m)

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Sample lD (nm) S0 ± 0.001 Sb ± 0.001

EPJ0 196.2 ± 7.71 0.4577 0.4859EPJ1 117.6 ± 6.04 0.4616 0.4831EPJ3 72.21 ± 5.04 0.4689 0.4830EPJ5 154.1 ± 9.81 0.4662 0.4836EPJ7.5 117.3 ± 6.48 0.4618 0.4818

• Decrease in diffusion length with clay loading (0-3%): Increase in the number of trapping sites (interfaces between clay and polymer).Exfoliation of clay at lower concentrations.

• Increase in Diffusion length at 5 % clay loading: formation of clay microparticles effectively reducing the no. of interfaces.

• Positron diffusion length follows bulk S-parameter profile.

Various parameters from VEPFIT analysis:

Chem Phys Chem, 13 (2012), 3916-3922

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Microstructural studies on the silver nanoparticles incorporated poly (perfluorosulfonic acid) membrane

Inclusion of the silver nanoparticles (AgNps) in host poly (perfluorosulfonicacid) membrane (Nafion-117) has been carried out

Two different reducing agents were used:Sodium borohydride (NaBH4), anionicFormamide, non-ionic

Nanoparticles (Nps) size were determined by XRD measurements

PALS was employed to measure free volume properties in the AgNps dopedand undoped Nafion membranes

Depth dependent S-parameter and Positronium fraction (3γ/2γ ratio)measurements have been carried out using variable slow positron beam

Journal of Physics: CS, 262 (2011), 012045, 1-4

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Nafion-117 One of the ion exchange membrane Selective permeability to cations (separation science) Low resistance to current flow (batteries and fuel cells) Excellent chemical, thermal and mechanical stability (industrial engineering)

Thickness : 178 m IEC: 0.91 mmol/g Density: 1.95 g/cc

Washed with deionized water

Nafion-117 with

organic impurities

Conc.HNO3

3-4 hrswashed with excess boiled water

Pure Nafion-117

1 hr

1 hr 1M HCl 1M NaOH

three times each

H+ form0.5M NaCl

30 hrs

0.25M AgNO3

48 hrsNa+ formAg+ form

30 mins

Na+/Ag

H+/Ag

C F 2

C F

C F 3

O HS

x y

z

C F 2

C F 2

C F 2

C F 2

C F 2

C F

O O O

OSample preparation:

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3 4 3 4[ ] [ ] [ ] [ ] [ ]mem aq mem aq memR SO Ag NaBH R SO Na BH Ag

The membrane samples were loaded with Ag+ ions by ion-exchange mechanism,

74 2 3 3 22[ ] [ ] 3 [ ] [ ] ( )o

aq mem aq memBH Ag H O H BO Ag H g

with Formamide, (distributed across the thickness of the membrane)0

3 2 2 3 22[ ] [ ] [ ] 2[ ] [ ] 2[ ]mem aq mem mem aq memR SO Ag HCONH H O R SO H NH COOH Ag

3 3[ ] [ ] [ ] [ ] [ ]mem aq mem aq aqR SO H NaCl R SO Na H Cl

3 3[ ] [ ] [ ] [ ]mem aq mem aqR SO Na Ag R SO Ag Na

with NaBH4, (near the surface region of the membrane)

Reducing agents AgNps size (nm) AgNps size (nm)Kumar et al., 2010

NaBH4 15 ± 5 15 ± 4

Formamide 10 ± 3 9 ± 2

XRD measurements:

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Among the ionic forms the most hydrated form has maximum o-Ps intensity andlifetime.

Ag+ is a good scavenger of electrons – inhibits the Positronium formation

Less o-Ps intensity in the nanoparticles doped membrane nanoparticles blocks the freevolume holes in the Nafion membrane

In Formamide case (H+/Ag), distinguishable change in the free volume nature

In NaBH4 case (Na+/Ag), marginal change in the free volume nature

Bulk characterization

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1.60

40( ) ( )Z E E

Implantation depth of positron depends upon positron energy and polymer density,

Surface analysis: depth dependent measurementsSlow Positron Beam Setup at Radiochemistry Division, BARC.

• In present case, the surface morphology (about 1 μm) is studied using the positronenergy range of 0.2 to 10keV

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• AgNps doped membranes shows high S-parameter values and high 3γ /2γratio

• increase in free volumes or high surface open porosity due to chemical reduction process

• Higher S-parameter value in Ag+ membrane with lower 3g/2g ratio is due to the formation of metallic silver layer at surface region

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Summary

Positron annihilation spectroscopy (PAS) complemented by conventionalcharacterization techniques has been used to investigate the correlations between thenanostructure and physico-chemical properties of polymers.

In chemically identical samples, the free volume size distribution plays a key role inthe swelling properties of the hydrogels.

The backbone chain length of polyether diamines plays a significant role indetermining the structural relaxations as well as macroscopic properties, which in turnexhibits the free volume properties in the epoxy systems.

Free positron trapping/annihilation events provide the information about the filler-matrix interfacial layers.