north carolina state university raleigh, north carolina, usa
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Fitting Polymers to the Demands of the Wet End: A subtle Balance of Interactions at the Nanoscale. Orlando J. Rojas, NC State. www4.ncsu.edu/~ojrojas. (see abstract t#22-0 in page 48). 2007 Nanotechnology for the Forest Products Industry 13-15, JUNE, 2007 | KNOXVILLE - PowerPoint PPT PresentationTRANSCRIPT
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
PolyelectrolytesMacroscopic
EffectsPolyampholytes
Order of Mixing Effects
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
Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale
IntroductionSimple
PolyelectrolytesMacroscopic
EffectsPolyampholytes
Order of Mixing Effects
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
++ + +++ ++ +
++ ++
++
+
Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale
IntroductionSimple
PolyelectrolytesMacroscopic
EffectsPolyampholytes
Order of Mixing Effects
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
Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale
IntroductionSimple
PolyelectrolytesMacroscopic
EffectsPolyampholytes
Order of Mixing Effects
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.
Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale
IntroductionSimple
PolyelectrolytesMacroscopic
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
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
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.
(Polymer + Surfactant) CoadsorptionOne step adsorption
Sequential adsorption
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
One-step Coadsorption Case
Polyelectrolyte + Surfactant Adsorption 1
+
+
++
+
+
Polyelectrolyte + Surfactant Adsorption 2
(Polymer + Surfactant) CoadsorptionOne step adsorption
Sequential adsorption
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
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
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
Not path dependant!
SDS Concentration (normalized cmc)
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
Fitting polymers to the demands of the wet end: A subtle balance of interactions at the nanoscale
IntroductionSimple
PolyelectrolytesMacroscopic
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