North Carolina State University Raleigh, North Carolina, USA

North Carolina State University

Raleigh, North Carolina, USA

www4.ncsu.edu/~ojrojas

2007 Nanotechnology for the Forest Products Industry13-15, JUNE, 2007 | KNOXVILLESurface Modification and CharacterizationSession Chair: Pete Lancaster, Weyerhaeuser

Fitting Polymers to the Demands of the Wet End: A subtle Balance of Interactions at the Nanoscale

Orlando J. Rojas, NC State

(see abstract t#22-0 in page 48)

IntroductionSimple

PolyelectrolytesMacroscopic

EffectsPolyampholytes

Order of Mixing Effects

Conclusions

Fitting polymers to the demands of the

wet end: A subtle balance of

interactions at the nanoscaleor

The Soft Side of Nanotechnology

Outline

Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale

IntroductionSimple




Conclusions

Introduction

Papermaking: A “Colloidal” Soup

Pulping & Bleaching

Chemical Additives Recycling & other process streams• dry strength resins

• wet strength resins• release emulsions• surfactants• retention aids• pitch control aids

• promoters• dyes• defoamers• slimicides• glue

• salts• dissolved & organic compd’s• suspended solids• carry-over chemicals

monolayer

colloidal pitch

biological organism

size precipitate oremulsion microdroplet

polymer

fibermicelle

surfactantmolecule

fines

entrained air

pigment/filler particlePolymers are

added as surfa

ce m

odifiers (fi

bers and fines)

Fiberparticles

Woodfiber Wood

fiber

1 mm

0.1 mmClayagglom-erates

PAMPAM

Fiberfine

Fiber

Bentonite

0.01 mm

Woodfiber

Cat. PAM

Fibrils

Amylo-pectin

Kaolin

PAM

TiO2

TiO2 Kaolin

Amylose

0.001 mm (1 µm)

Fiberwallfibrils PAM

Amylose

TiO2

Bentonite

TiO2

Colloidalsilica

TiO2

Kaolin

Amylopectin


IntroductionSimple




Conclusions

Simple Polyelectrolytes (PE)

(and the Effect of PE Charge Density)

How do surface modifiers affect adhesion and macroscopic properties of papermaking

surfaces?

Interaction forces are difficult to measure and understand

Complex nature of fiber (and mineral) surfaces (chemical and morphological)

Subtle balance of interactions at the nanoscale

Simple Polyelectrolytes PE (+)

CH

C=O

2CH( )

n

NH2

acrylamide (AM )

3CH

CH2

3CH

3CH

C

C=O

CH2

CH2

N3

CH+

Cl-

2CH( )

n

NH

[3-(2-methylpropionamido)propyl] trimethylammonium chloride (MAPTAC ) +

+ ++

+

(charge density): 1, 10, 30, 100% (Mw= 1M)

++ + +++ ++ ++

+

+

Substrates Silica, glass, mica and cellulose(-)

Al KX-Ray

1486.6 eV

polyelectrolyte

x

IAIA

h

Photoelectron

K

L1

L2,3

ExcitationEmission

mica

C1s O1s Si2p K2p N1sXPS to QuantifyPolyelectrolyte Adsorption

IN

IK

NN

NK

NN

Amg Polyelectrolyte

A

Rojas et al., J. Phys. Chem. B, 104(43): 10032-10042 (2000)

Bimorph surface force apparatusMeasurement and Analysis of Surface and Interfacial Forces

Surfaces

Teflon diaphragm

Motor translation

Piezo tube LVDT

Teflon seal

Bimorph Teflon sheath

To charge amplifier...

Clamps for the bimorph

Polyelectrolyte Adsorption

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 100 200 300 400 500

PE (=1%) Concentration, g/ml

XPS/Mica

mg/

m2

Equilibrium Adsorption

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 1000 2000 3000 4000 5000 6000Time, s

mg

/m2

Ellipsometry /Silica

Adsorption kinetics

J Colloid Interface Sci. 205:77 (1998)

XPS detailed N 1s spectrum for cellulose after immersion

in 0.1 mM KBr solution

XPS detailed N 1s spectrum for cellulose after immersion in 0.1 mM KBr containing 200

mg/L of polyelectrolyte

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 50 100 150 200

Polyelectrolyte Concentration, g/mL

Ad

so

rbe

d P

oly

ele

ctr

oly

te,

mg

/m2 Mica

LB-Cellulose

Adsorption Isotherms XPS – N1s

XPS – N1s

Polyelectrolyte Charge Density -Adsorbed Amount and Conformation at the Interface

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100Ads

orbe

d P

olye

lect

roly

te, m

g/m

2

Langmuir 18: 1604 (2002)

Polyelectrolyte Charge Density, %

Nanoscale Interaction Forces!What are their implications at the macroscale?

Intl J Mineral Process, 56: 1–30 (1999).

Interaction ForcesIn

tera

ctio

n E

ner

gy

0

Double-layer repulsion

van der Waalsattraction

Total energy

Distance

Distance, nm

10

100

1000

10000

0 20 40 60 80 100

10000

0 20 40 60 80 100

F/R

, N

/m

Steric forces!A

ttra

ctio

n (

-)R

epu

lsio

n (

+)

DLVO

Cat. PE = 1%Adsorbed Conformation

and Adhesion

Distance, nm

F/R

, N

/m

10

100

1000

10000

0 20 40 60 80 100

s

c

P Dk T

s

L

D

D

LB( )

/ /

3

9 4 3 42

2

Alexander-de Gennes fit(elastic and osmotic contributions)

Loop density= 2.02x1017 loops/m2

Tail density= 3.34x1015 tails/m2

17 nm (24 nm from Alexander-de Gennes fit)

c=5-8 nm

s=50 nm

10% of mica charges are compensated

AM-MAPTAC-1 copolymer = (AM101 MAPTAC) 122

0.45 nm

tailloop

Stericrepulsion

JCIS 205: 77 (1998)

0.01

0.1

1

10

0 20 40 60 80 100

Apparent Separation Distance, nm

F/R

, m

N/m

DLVO fit

Electrostericrepulsion

Interpenetration & bridging adhesion

adhesion

Cat. PE = 10%Adsorbed Conformation

and Adhesion

Adv. Colloid Interface Sci 104: 53 (2003)

Force normalized by radius between surfaces precoated with various polyelectrolytes in aqueous 0.1 mM KBr solution. The arrow indicates an inward jump and the vertical

lines the layer thicknesses for adsorbed polyelectrolytes.

100%30%

10%

1%

-0.5

0

0.5

1

1.5

2

0 200 400 600 800

Distance (Å)

F/R

(m

N/m

)

Langmuir 18: 1604 –1612 (2002)

0.0

0.5

1.0

1.5

0 10 20 30 40 50 60 70 80 90 100

Polyelectrolyte Charge Density, %

Ch

arg

e N

eutr

aliz

atio

n

Flocculation & Stabilization

Steric repulsionBridging flocculationPatch &

Charge reversalre-dispersion

++ + +++ ++ +

++ ++

++

+


IntroductionSimple




Conclusions

Macroscopic Effects

(two cases: retention and adhesion)

Adsorption of Guar Gums (GG)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

Dosage, mg/g

Ab

sorb

an

ce

201510500.0

0.2

0.4

0.6

0.8

1.0

Dosage, mg/g

Ab

sorb

an

ce

low cationic GGwhole pulp

high cationic GGwhole pulp

201510500.0

0.2

0.4

0.6

0.8

1.0

Dosage, mg/g

Ab

sorb

an

ce

underivatized GGwhole pulp

201510500.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Dosage, mg/g

Ab

sorb

an

ce

anionic GGwhole pulp

= charge density

Adsorption of Guar Gums (GG)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

Dosage, mg/g 201510500.0

0.2

0.4

0.6

0.8

1.0

Dosage, mg/g

low cationic GGwhole pulp

high cationic GGwhole pulp

201510500.0

0.2

0.4

0.6

0.8

1.0

Dosage, mg/g

underivatized GGwhole pulp

201510500.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Dosage, mg/g

anionic GG

whole pulp

= charge density

Dis

solv

ed a

nd

Co

llo

idal

Car

bo

hyd

rate

s,

g/g

0

10

20

30

40

50

0 5 10 15 20 25

Dosage, mg/g

% F

ines

Ret

entio

nlow DS cationic GG

whole pulp

Fines Retention

25

30

35

40

45

50

0 5 10 15 20 25

Dosage, mg/g

low cationic GG(whole pulp)

Colloids & Surfaces A.155, 419-432 (1999)

ADHESION:

Symmetrical Systems

Asymmetrical Systems

PE layer thickness increase of 0.5-1 nm

PE stretching:

Surface contact

On separation:

r/r0 =0.65-0.75 (0.63 JKR)

(*) Note: Contact area on separation: stick-slip behavior

High charge density polymers:

PE collapses in different conformation

extensiveBRIDGING

0

1000

2000

3000

0 20 40 60 80 100

Charge density (%)

F/R

(m

N/m

)Effect of PE Charge

Density on Adhesion

Decreasing importance of electrostatic bridging

1st

5th sep.

Interpenetration and entanglement

layer is disrupted

Langmuir 20(8):3221-3230 (2004)

Paper strength:

Fiber intrinsic strength

Bond strength

Number of bonds

Fiber and bond distribution

Charge density of pulp fibers

Fibers are dried in close proximity (surface tension and capillary effects).

Larger chances for polymer layers to interpenetrate and interlock

Polyelectrolyte charge density: important effect on adsorbed state (“surface modification”)

Interaction forces at the nanoscale: shapes up macroscopic phenomena (e.g., retention and adhesion)

PE charge density key in adhesion development.

Evidence of formation of electrostatic bridges (for PEs with high charge density).

Entanglement: contributes to adhesion in the case of PEs of low charge density

Conclusions I


IntroductionSimple




Conclusions

Polyampholytes

(H3C)2N

N H2

HO

H O

OO

O

m100-n-m

n

Itaconic acid monomer group

Acrylamide monomer group

Dimethylaminoprolylacrylamide (DMAPAA) monomer group

O

NH

Polyampholytes

Synthesis of acrylamide-based polyampholytes and copolymers

Sam-ple

Polymer Type

DMAPAA

mol %IA

(mol %)Mw **

(106 Daltons)

A Amphoteric 2.5 1 2.95

B 5 2 2.85

C 10 4 2.90

D 20 8 2.93

F Cationic 5 0 2.98

G Anionic 0 2 3.23

** Mass-average molecular mass evaluated by SEC-LALLS-VIS (TDA-302, Viscotek).

Increasing charge

Polyampholyte in solution

Initial adsorbed conformation

Negatively Charged Substrate

Adsorption

Time Time

Conformation after rearrangement

Expected conformational changes following adsorption of a polyampholyte in which the distribution of charged groups

is segregated

SP vs pH: HW FBG

Kraft fiber

Poly-acid (-) G

Poly-base (+) F

Poly-ampholyte B

-20

-15

-10

-5

0

5

10

pH

Blank

2 4 6 8 10 12

Str

eam

ing

Po

ten

tial

(m

V)

SP vs pH: HW Fiber

Kraft fiber

Increasing charge

-16

-12

-8

-4

0

4

8

pH

Blank

A

B

C

D

2 4 6 8 10 12

Str

eam

ing

Po

ten

tial

(m

V)

Increasing charge

Poly-base (+) F

Poly-ampholyte B

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3 4 5 6 7 8 9 10 11

pH

Ad

sorb

ed A

mo

un

t (

g/1

00g

pu

lp)

B, 5% cat, 4% an

F, 5% cationic

Adsorption vs pH

NPPRJ 21(5): 638-645 (2006)

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Blank A B C D F G

pH=5

pH=8.5

pH=4

Polymer (1% Treatment Level)

Bre

akin

g L

eng

th (

km)

Bleached HW Kraft Fibers

JPPS 32(3): 156-162 (2006)

Conclusions II

Polyampholytes: interesting alternative to fine-tune (surface) properties of fiber and fiber networks.

Strength is related with the mass of polymer adsorbed:

Broad maximum in polyampholyte adsorption in pH range 6 to 9, greatly exceeding adsorbed amounts of corresponding polyelectrolytes

There appears to be an optimum charge density of polyampholytes to provide strength gains in paper.


IntroductionSimple


EffectsPolyampholytes Mixing Effects Conclusions

Mixing Effects

The effects of polymer/surfactant interactions on adsorption and adhesion remain difficult to predict

suspensions and slurries: pigment, paper, printing and

coating formulations.

Polymers and surfactants are included in fluid formulations to achieve independent objectives.

Polymers are intended to control rheology

Surfactants are intended to control capillarity

Surfactant binds to polymer surface is selective (type I)surface is non-selective (type II)

Surfactant does not bind to polymersurface is selective (type III)surface is non-selective (type IV)

Polymer-Surfactant-Surface Systems

Our case: Selective Surfaces I

Polymer (+) & Surfactant (-)Polymer (+) & Surfactant (-)

+ ++

= 10%

+ ++

++ +++ +

++

+

++

+

Na dedecyl sulphate (SDS)

OS

O

O

O-

CH

C=O

2CH( )

n

NH2

acrylamide (AM )

3CH

CH2

3CH

3CH

C

C=O

CH2

CH2

N3

CH+

Cl-

2CH( )

n

NH

[3-(2-methylpropionamido)propyl] trimethylammonium chloride (MAPTAC ) +

(Polymer + Surfactant) CoadsorptionOne step adsorption

Sequential adsorption




How do adsorbed polyelectrolytes respond to changes in surfactant concentration?

Mixed (polyelectrolyte/surfactant) coadsorption

Challenge:

Understand the origins of the synergies in polymer systems and rationalize issues related to processing history.

One-step Coadsorption Case

Polyelectrolyte + Surfactant Adsorption 1

+

+

++

+

+

Polyelectrolyte + Surfactant Adsorption 2

Sequential Coadsorption CasePolyelectrolyte +

Surfactant Adsorption

+

+

+

New solution, higher surfactant conc.

+

+

+

rinsing

++

+

Coadsorption…Coadsorption…

PE = 10% / SDS / silica

SDS Concentration (normalized cmc)

0 0.1 0.5 2 Rinse

Effe

ctiv

e O

ptic

al T

hic

kne

ss (

nm

)

0.1

0.2

0.3

0.4

0.5

0.6

Su

rfa

ce C

on

cen

trat

ion

(m

g/m

2)

0.6

1.2

1.8

2.4

3.0

3.6

4.2

Sequential adsorptionOne-step adsorption

Layer of aggregates

Coadsorption…Coadsorption…

PE = 10% / SDS / silica


0 0.1 0.5 2 Rinse

Effe

ctiv

e O

ptic

al T

hic

kne

ss (

nm

)

0.1

0.2

0.3

0.4

0.5

0.6

Su

rfa

ce C

on

cen

trat

ion

(m

g/m

2)

0.6

1.2

1.8

2.4

3.0

3.6

4.2

Sequential adsorptionOne-step adsorption

Layer of aggregates

Not path dependant!


0 0.1 0.5 2 Rinse

++

+

++

+

++

++

+

++

+

+

+

+

+

+

++

++

+

+

+

+

+

+

+

+

+

+

v+

+

+

++

+

++

+

++

+

+

+

+

50 nm

++

+

+

+

+

50 nm

++

+

0 SDSOn approach: Electrosteric interaction forcesOn separation: Adhesion, interpenetration and bridging

0.1 and 0.5 × cmc SDSOn approach: compression of thick layer of aggregatesOn separation: No Adhesion

2 × cmc SDSOn approach: Electrosteric interaction forcesOn separation: Reappearance of Adhesion interpenetration and bridging

Interaction forces

Reversibility! (the exception to the “rule”)

Type I co-adsorption systems:

In most cases the composition and

structure of the adsorbed layers

depends on the order in which the

surface is exposed to surfactants

and polymers.

Not in our case…

(Polymer + Surfactant)(Polymer + Surfactant)CoadsorptionCoadsorption

Type I systems

(surfactant and polymer associate in solution and the surface is selective for the polymer)

[AM-MAPTAC + SDS] / SILICA

[PEO-PPO-PEO + SDS] / SILICA

Polymer adsorbs irreversibly.

Mixed layers respond reversible to

changes in surfactant

Strongly path-dependent

coadsorption

Strong Surfactant-Polymer affinity

Weak Surfactant-Polymer affinity

[cellulose (HPC or hmHEC) + SDS] / SILICA

Strong Polymer affinity

+

+

+

+

+

++

+

+

+

++

Weak Polymer affinity

+

+

+

+

++

+v

+

+

+

++

Segments “solubilized”.More loops and tails.

++ ++

++

++

+ ++

+

+

+ ++

+ +

+

+ ++ +

SDS stripped off.More train segments.

X

Weak Polymer affinity

+

+ ++

++

++

+ ++ +

++ ++

++

+v

+

+ ++

+

+

+

+

+

++

+v

+

+

+

++

Strong Polymer affinity

+

+

+

v+

++

+v

+

+

+

+v+

Segments “solubilized”More loops and tails

SDS stripped off.More train segments

Activation barrier (against polymer

desorption or rearrangement) is

small

No capacity to respond to changes.

Path-dependant coadsorption

Conclusions III

Mixed adsorbed layers respond reversibly to changes in the concentration of SDS in a mixed PE / SDS solution

Most common cases: Path-dependent co-adsorption (hysteretic) (characterized by persistent non-equilibrium states at interfaces).

Balance of affinities: explains hysteretic effects


IntroductionSimple


EffectsPolyampholytes Mixing Effects Conclusions

Conclusions

Papermaking wet end: adsorption from polymer mixtures to the solid-liquid interface is a critical aspect of the process.

Interaction forces, balance of charges and adsorbed mass dominates cause-effect relationships (from the nano- to the macro-scales!)

Soft side of “Fiber Nanotechnology”:

Kelley Spence:Self Assembly

Monolayers of Cellulose

Dr. Montero: Cellulose

Nanocrystals Electrospinning &

Lignin Thermal Properties

Dr. Kim: Cellulose Nanorods and

Electrospinning of Cellulose

Nanocrystal Composites

Hongyi Liu: Boundary

Layer Lubrication

and Molecular Dynamics Simulation

Junlong Song: Polyampholyte Adsorption, Boundary Layer Lubrication and Molecular Dynamics Simulation

Chang Woo Jeong: Enzyme Activity via

piezoelectric Sensors, Thin films and Boundary

Layer Lubrication

Dr. Xavier Turon: Enzyme Activity via

piezoelectric Sensors and Molecular

Dynamics Simulation

Wes Crawford: Surfactants in Paper

Recycling

Special thanks to Prof. Martin Hubbe, Dr. Xingwu Wang and Yun Wang.

Generous support from the National Research Initiative of the USDA Cooperative State Research (grant number 2004-35504-14655); Harima Chemical Co., and NCSU Nanotechnology Seed Grant are acknowledged.

Acknowledgments

Thanks for your attention

North Carolina State University Raleigh, North Carolina, USA

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