1. Rheology of
Polyelectrolyte Multilayer Modified Suspensions
PHD Talk, Andreas Hess
23 April 2013

2. Outline
PEMs for suspension modification?
Effect of polyelectrolyte layer number on
rheology.
Effect of terminating polyelectrolyte on
rheology.
Tuning the yield stress of polyelectrolyte
multilayer modified suspensions.
2 / 18

3. Motivation for PEM Modified Suspensions
Cartoon of the zoo of colloidal systems∗
∗M. Cloitre, High Solid Dispersions, Adv. Polym. Sci., Vol. 236 (2010)
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4. Polyelectrolyte Multilayer Modification
PDADMAC PSS
Surface charge reversal
-80
-60
-40
-20
0
20
40
0 2 4 6 8 10 12
ζ(mV)
# layers
Template: 5 µm Polystyrene sphere
Layer-by-layer self assembly∗
Suspension:
φ = 0.55 (Glycerol)
φ = 0.4...0.6 (water)
∗G. Decher et al., Science 277, 1232 (1997)
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5. Topography of Polyelectrolyte Multilayers
(PAH/PSS)n multilayers onto Si-Wafer∗:
500 nm
n=2
500 nm
n=6
(PDADMAC/PSS)n multilayers onto 5 µm PS-Sphere+
:
n=2
100 nm
n=8
100 nm
20 nm
0 nm
∗V. Bosio et al., Colloid. Surface A 243, 147 (2004) +A. Hess et al., Phys. Rev. E 84, 31407 (2011)
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6. Precursor and Multilayer RegimeForce
Distance
Force
Distance
Force
Distance
Precursor regime (n=2) Multilayer regime (n=6)
Force
Distance
Force
Distance
Force
Distance
Cartoon after V. Bosio et al., Colloid. Surface A 243, 147 (2004)
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7. Connecting Particle Interactions with Macroscale Rheology
Microscopic picture of yielding:
1
2
3
4
5
6
Local strain
U
Macroscopic measures:
Shear modulus:
G ∝ U′′
(r0)
Yield stress:
σy ∝ U′
(ry )
U
U0
Slope U'(ry)
Curvature U''(r0)
r0 ry r
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8. Detecting the Multilayer Regime by Macroscale Rheology
10−2
10−1
100
0 2 4 6 8 10 12 14
σy/G
# layers
Bare particles
PSS terminated
PDADMAC terminated
Precursor regime Multilayer regimeTransition
A. Hess et al., Phys. Rev. E 84, 31407 (2011)
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9. Typical Dense Suspension Flow Curve
logσ
logγ, log ˙γ
σh
σy
1
1
Newtonian
Shear thickening
Shear thinning
Solid-like
G
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10. Modeling the Flow Behavior
Extended Herschel-Bulkley model∗:
σ ( ˙γ) = σy
Yield stress
+ a1 · ˙γ1/2
Shear thinning-
+ a2 · ˙γ1/ε
Shear thickening stress
10−2
10−1
100
101
102
10−5 10−4 10−3 10−2 10−1 100 101
σ(Pa)
˙γ (s−1)
Experiment+
a1 ˙γ1/2
a2 ˙γ1/ε
Extended Herschel-Bulkley
∗E. Brown et al., Nature Materials 9, 220 (2010) +A. Hess and N. Aksel, Soft Matter (in review)
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11. Layer Dependence of the Shear Thickening Stress
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12
a2(Pas)
# layers
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10 12
1/ε
# layers
10−3
10−2
10−1
100
101
102
102 103 104
105
106
σ/σh
Pe
Bare particles
PSS terminated
PDADMAC terminated
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12. Origin of the Shear Thickening
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12
a2(Pas)
# layers
-80
-60
-40
-20
0
20
40
0 2 4 6 8 10 12
ζ(mV)
# layers
Force balance at the onset of shear thickening:
σh
Hydrodynamic force
∝ ζ2
Electrostatic force
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13. Origin of the Shear Thickening
10−1
100
101
103 104
σh(Pa)
ζ2 ·aφ (mV)2
1
Cartoon of PEM membranes∗
aPDADMAC
φ = 2·aPSS
φ Permeability ∆PDADMAC
= 2·∆PSS
Modified force balance at the onset of shear thickening&
:
σh ·∆−1
Modified hydrodynamic force
∝ ζ2
Electrostatic force
∗M. L. Bruening et al., Langmuir 24, 7663 (2008) &V. Gopalakrishnan et al., J. Rheol. 48, 1321 (2004)
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14. Tuning the Yield Stress at Fixed Layer Number
Yield stress∗:
σy ∝
φνU
a2
Particle size a (=const.)
Volume fraction φ
Interaction potential U
10-3
10-2
10-1
100
101
10-2 10-1 100 101 102
σ(Pa)
˙γ (s−1
)
(a) I = 500 mM KCl
φ
10-3
10-2
10-1
100
101
10-2 10-1 100 101 102
σ(Pa)
˙γ (s−1
)
(b) I = 1 mM KCl
φ
∗A. R. Studart et al., Soft Matter 7, 6408 (2011) A. Hess and N. Aksel, Langmuir (in review)
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15. Tuning the Yield Stress at Fixed Layer Number
PEMs assembled at:
1 M KCl (brush-like)
10 mM KCl (rod-like)
salt concentration
-
-
- -
- -
- -
-
-
-
-
-
--
--
- -
-
-
- -
-
-
--
-
-
-
-
rod-like brush-like
10-3
10-2
10-1
100
101
102
10-1 100 101 102 103 104
σ·a(Pa)
˙γ ·b/η∞ (s−1
)
brush-like
rod-like
10-1
100
101
102
103
10-1
100
101
102
103
a
b/η∞
1
A. Hess and N. Aksel, Langmuir (in review)
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16. Conclusions
The rheology is sensitive to polyelectrolyte multilayer modification.
The rheology is independent of the layer number in the multilayer
regime.
The rheology depends on the terminating polyelectrolyte.
The yield stress can be tuned by the polyelectrolyte conformation
during PEM assembly.
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17. Synthesis of 5 µm polystyrene particles
Reaction flask contains 200g
particles after washing.
⊲ Dispersion polymerisation1, 2
:
difficult to control the particle size
→ premixing starter (AMBN) with little amount of
styrene
PVP and Triton X-305 as stabilizers
synthesis in water/ethanol mixtures
⊲ Particle size:
light scattering (Malvern Mastersizer2000)
→ polydispersity: 0.03 (quasi-monodisperse)
REM
→ diameter: 5±0.1 µm
→ non-porous
1
Lok et al., Can. J. Chem., 63, 209 (1985)
2
Song et al., J. Am. Chem. Soc., 126, 6562 (2004)
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18. Particle Synthesis - Size Distribution
Batch no.
127
129
130
132
Mixing several syntheses batches is possible! 18 / 18