Presented to American Oil Chemist's Society May 2014

1. Quantifying Adsorption of Surfactants and
Polyelectrolyte Complexes at the Solid-Liquid
Interface by Quartz Crystal Microgravimetry with
Dissipation (QCM-D)
Mona M. Knock
Advanced Measurements Sciences
Mike Kinsinger, David R. Scheuing
Advanced Technology
Clorox Technical Center, Pleasanton CA
ANA 1.1 / S&D 1.2 #42420; May 2, 2011
Phase Behavior and Characterization of Polyelectrolyte
Complexes (PECs)
AOCS Meeting – May, 2014
D.R. Scheuing, Mona M. Knock
Clorox
S&D 3.0 – General Surfactants

2. Outline
What Are PECs & How To Make Them
What Can PECs Do?
Characterization of PECs in Solution
Characterization of PECs on Surfaces
2

3. PECs Are Self-Assembling Aggregates of Oppositely Charged Polymers
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Ladder – Molecular
Level
or
Scrambled Egg -
Multiple Chains in
Particle
Ref. 1,2,6
Driving Force – Entropy Gain From Release of Small Counterions

4. PEC Formation Requires Balance of Entropic and Electrostatic
(Enthalpic) Energy Contributions
Entropic part –
• Small Entropy loss due to restrictions on polymer chains
• Large Entropy gain from release of small counterions
Electrostatic –
• Favors close association of PE charges in a phase
• Phase Separation and/or Precipitation Favored
• Stop Phase Separation at Colloidal Dimensions Yields Stable Particles
Let’s define “R” = moles
(equivalents) of cationic
charges/moles (eq) of
anionic charges –
R= +/-
Non-Stoichiometric PECs Are
Stabilized By the Electrostatic
Charges of Excess Component

5. PEC Synthesis in Aqueous Systems – Driven By Chain Dynamics
5
Polymer type – Strong Acid (styrene
sulfonate), Strong Base (DADMAC quat)
Little pH Dependence
Polymer type – Weak Acid (acrylic,
methacrylic acid), Weak Base (chitosan,
ethyleneimine )
Major pH Dependence
PECs Made in Pure Water – “Frozen” Non-Equilibrium Structures
PECs Made in Water + Electrolyte – Dynamic Living Systems
High MW Chains Favored, Sulfonates Displace Carboxylates 1
Assemble Stable PECs from Dilute PE Solutions !
Total Polymer – 0.01 – 0.1 wt% , or < 10 (meq/l or mM) of total charges 1,10

6. What Can PECs Do?
6
Specialized Membrane Production
1,2
Drug Delivery 3
PECs Layers on Particles – Sensors, Protein Immobilization
7,8
PECs Layers on Hard Surfaces – Hydrophilic/Hydrophobic
Surface Modification 9
PECs with DNA – Gene Therapy 4
Carolin Ganas, Michael Gradzielski
(Stranski-Laboratorium für Physikalische
und Theoretische Chemie, Institut für
Chemie, Technische Universität Berlin,
Germany)
Flocculants 1,2
Cartilage Mimics, 5

7. Characterization of PECs in Solution
7

8. Multi-Angle Light Scattering (MALS) in
Batch Mode
Simultaneously obtain:
• Absolute Molecular Weight (Mw)
• Second Virial Coefficient (A2)
• RMS Radius (Rg)
Characterization Via Static Light Scattering
c = Concentration of Solute
Excess Rayleigh Scattering
As Function of Angle and
Concentration
Angular
Dependence of
Scattered Light –
Yields RMS
Radius of
Aggregate
Weight Average
Molar Mass
2nd virial
coefficient
Optical
constant
*Wyatt Corp.
*

9. Chitosan/Poly(acrylic acid) PECs
Chitosan
Natural, edible, bacteriostatic, cationic PE at “low”
pH
Cationic Amine
groups for interaction
electrostatic binding
with PAA
Chitosan – weak base PE – water soluble only at pH < 6.
Readily Soluble as citric acid salt @ pH 2.0
Poly(acrylic acid) – weak acid PE. Well below pKa @ pH 2.0.
Will Chitosan/PAA PECs Form ?

10. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
0.0
500.0k
1.0M
1.5M
2.0M
2.5M
3.0M
3.5M
4.0M
Mw
(g/mole)
Amine/Acid Ratio
Static Light Scattering Confirms PEC Formation at Acidic pH and
Presence of Multiple Polymer Chains in Each PEC
PECs MW = 4 million !
Polymers are about 60K each
R = Chitosan/PAA – 2mM Total Polymer
pH = 2.2, [Citric Acid] = 0.7 %

11. Dynamic Light Scattering Measures the Correlation Curve
– Size is Calculated
11
212
)],([1),(  qgqg 
)exp(),(1
 qg
tDq2

Monodisperse particles
Decay rate
Diffusion
coefficient
Gaussian Distribution of Diffusion
Coefficients – Use “Cumulants Method” to
Fit Decay
Z – average
Diffusion
Coefficient
Polydispersity
Index (PDI)
Z-average Size Is Intensity-Weighted – Because Intensity Is Measured
If PDI <0.5 – Compare Z-average directly
If PDI >0.5 – Compare the Distributions of Samples Measured in Same Medium
*Zeta Sizer Nano Manual – Malvern Corp
*
*
*

12. Velocity of Particles in Field Measured – Zeta Potential is
Calculated
12
Electrophoretic
Mobility – Velocity
of Particle
Henry’s function –
approximately =
1.5
ViscosityDielectric
constant
Zeta
Potential
Folded Capillary Cell
(Malvern)
Particle Motion Causes Time-Dependent Intensity
Variation of Laser Light = Frequency/Frequencies
~ Velocity Distribution
PALS = Phase Analysis Light Scattering – Read Phase Shift of
Laser Light – Better Sensitivity
Malvern Applies Clever Field Reversal Sequences to Overcome
Capillary Wall Effects (M3)
*Zeta Sizer Nano Manual – Malvern Corp
*
*

13. Size Distributions of DADMAC/PAA PECs From DLS Show Shifts with
R (DADMAC cationic equivalents/PAA acid equivalents)
13
Polydispersity range = 0.063 – 0.165. Z-average diameters may be
compared.
polyDADMAC = Floquat 5240 (SNF)
Poly(acrylic acid) = Aquatreat AR-4 (Akzo Nobel)
Total polymer concentration constant 2 mM charges (2 meq/l) (< 0.025 wt%)
R=0.75
R=0.25
R=1.0
R=2.0
PECs From a Strong (Quat) and Weak (Carboxylic Acid) Polyelectrolyte
pH = 10. 5

14. DADMAC/PAA PECs Are “Living” Systems – Behavior Shifts
As pH Is Decreased
14
PECs Unstable at pH 10-
10.5 0.85 < R < 0.95
PECs Unstable at pH 3.0
R < 0.30
PECs Are Large Near
Phase Boundary – High pH
PECs Are Smaller at
Extremes of R @ pH 7 –
10.5
At pH 3.0, PECs
crash at low R value
Triplicate measurements % RSD
< 3.0% = Symbol Size
PDI < 0.25 for all samples

15. Zeta Potential of + or – 30 mV Stabilizes
DADMAC/PAA PECs
15
Unstable Region,
pH 7-10.5
Unstable Region,
pH 3.0
PECs Unstable in
Region of Charge
Reversal
At pH 3.0 – PECs are
Cationic Even at R < 1.0.
Most Acid Groups Are
Protonated. DADMAC
charges stabilize PECs.
At pH 3.0, R=0.25, Ppt.
Formed Due to Strong
DADMAC/Acid
Interactions. Chain
Dynamics Differ From
Chitosan/PAA !
Triplicate Measurements, %RSD
<10% (error bars) for all samples

16. What Can PECs Do?
16
Surface Modification & Engineering

17. IRE
(Ge)Air
Sampling depth, dp= 736
nm at 1650 cm-1
dp = l/2p (sin2 q  n21
2 )1/2
Refractive index = n2 = 1.5
Refractive index = n1=
4.0
q
n21=n2/n1
PECs On Surfaces – Fourier Transform Infrared Spectroscopy with Attenuated
Total Reflectance (ATR) Sampling Optics Can Probe Adsorbed Monolayers

18. 50 mm
Trough on Horizon rig
Commercial Optics Enable Controlled Exposure of a Ge
Surface to PECs Solutions
2.5 mL trough
Dry Nitrogen/Air
Input
Images of “Horizon”
from Harrick, Inc.
PECs Solution

19. DADMAC/PAA PECs Adsorb on Anionic Ge Surface at
both R>1 and R<1 – and Hydrate in Air Readily
Total Polymer Concentration – 1.7mM, pH 12.0, electrolyte = 0.12% NaCl,
5 minutes adsorption time

20. FT-IR Band Shifts Indicate Water Uptake Swells Adsorbed
DADMAC/PAA Layers – Polymer Chain Dynamics Persist
20
Carboxylate Bands (PAA) Shift Due to Increase in Distance To
DADMAC Quat Group “Counterion” 11. Water Uptake Obvious.

21. 21
PECs On Surfaces - Quartz Crystal Microbalance with
Dissipation (QCM-D) Measures Adsorption
Oscillating Crystal
– Silica Surface
PECs Solutions and Rinse Solutions Flow
Across Crystal @ 150 microliters/min,
Temperature Controlled at 25 ºC
*
*Q-Sense

22. 22
Quartz Crystal Microbalance with Dissipation: Solid-Liquid
Interface: Sauerbrey Relation
• crystal oscillates under applied AC voltage
• frequency (f) depends on oscillating mass, including
coupled water
• f decreases when thin film attached to crystal
• f decrease proportional to film mass, if film thin & rigid
• film mass (m) calculated by Sauerbrey relation:
∆m =  ∆f C / n
• C = 17.7 ng Hz-1 cm-2 for a ~5 MHz quartz crystal
• n = 1,3,5,7,9,11 is the overtone number
Here, we use the Sauerbrey model, as our films are not viscoelastic.

23. Net Cationic PECs Adsorb on Silica and Resist Rinsing with
Brine
23
NaCl
Rinse
Water
Rinse
Multiple Adsorption/Water
Rinse
Initial Maximum Adsorption
201 ± 26 ng/cm2
After NaCl Rinse
133 ± 20 ng/cm2
Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl.
Flow rate constant at 150 microliters/minute

24. Net Anionic PECs Adsorb on Silica – And Show Dynamic
Responses to Rinses
24
Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl
Multiple Adsorption/Water
Rinse
NaCl
Rinse
Water
Rinse
Initial Adsorption
398 ± 43 ng/cm2
After Water Rinses
235 ± 42 ng/cm2
After NaCl rinse
146 ± 47 ng/cm2

25. Adsorbed Amounts of PECs Converge Only After Extensive Rinsing.
Net Anionic PECs Differ in Chain Dynamics from Net Cationic PECs
25
Sauerbrey relation
was maintained for
both samples !

26. Summary
26
Polyelectrolytes of opposite charge can form PECs due to the overall
entropy gain from loss of small counterions
PECs can be assembled in dilute solutions and stabilized by the
charge of the polymer in excess
Static and Dynamic Light Scattering Can Be Readily Applied to
Characterization of PECs at < 5 mM total polymer concentrations.
PECs with diameters of 50 – 250 nm with zeta potentials of 30 mV (+ or
-) are found to be quite stable in solution
FT-IR spectroscopy with ATR optics confirms that PECs designed to
have living chain dynamics adsorb rapidly onto surfaces.
QCM-D can measure PECs on surfaces near 100 ng/cm2.
Confirmation of anionic PECs adsorbing on anionic surfaces due
to dynamic chain re-arrangements is also obtained.

27. Thanks !
27
Clorox
S&D Division & AOCS
You –
The Audience and
Consumer !

28. Appendix
28

29. References
29
1. Dautzenberg, H. in Surfactant Science Series #99 - Physical Chemistry of Polyelectrolytes, Chap 20, Marcel Dekker,
2001
2. Michaels, A.S., Miekka R.G. J.Phys.Chem. 1961, 65(10), 1765-1773(a)
3. Martin Müller, Bernd Keßler, Johanna Fröhlich, Sebastian Poeschla and Bernhard Torger ,Polymers 2011, 3, 762-778;
doi:10.3390/polym3020762
4. Alexander V. Kabanov ,Victor A. Kabanov , Advanced Drug Delivery Reviews 30 (1998) 49–60
5. Haifa H. Hariri, Joseph B. Schlenoff, Macromolecules DOI: 10.1021/ma101297
6. Katja Henzler,Bjorn Haupt,Karlheinz Lauterbach, Alexander Wittemann, Oleg Borisov, Matthias Baliauff J.AM.CHEM.
SOC. 2010, 132,3159-316
7. G.Decher, M.Eckle, J.Schmitt,B.Struth, Current Opinion in Colloid Interface Science, 1998, 3 (1), 32-39
8. G.Decher, B.Lehr,K.Lowack,Y.Lvov,J.Schmitt Biosensors Bioelectronics 1994, 9:677-684
9. Quantifying Adsorption of Surfactants and Polyelectrolyte Complexes at the Solid-Liquid Interface by Quartz Crystal
Microgravimetry with Dissipation (QCM-D), Mona M.Knock, Mike Kinsinger, D.R.Scheuing, presented at AOCS
meeting 2011, ANA 1.1 / S&D 1.2 #42420
10. Heide-Marie Buchhammer, Mandy Mende, Marina Oelmann, Colloids and Surfaces A: Physicochem. Eng. Aspects
218 (2003) 151-159
11. J.Umemera, H.H.Mantsch,D.G.Cameron J.Colloid Int.Sci. 83 (2) 558 (1981)

30. Net Cationic PECs Adsorb on Silica and Are Quite Resistant to
Water Rinsing
30
Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl
Adsorption Maximum -
174 ± 13 ng/cm2
After Rinsing 4 hours
135 ± 16 ng/cm2
Start Water
Rinse
Extremely Rapid Initial
Adsorption

31. Net Anionic PECs Adsorb on Silica And Can Also Resist
Water Rinsing
31
387 ± 7 ng/cm2
229 ± 4 ng/cm2
Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl
Start Water
Rinse

32. 32
• Autocorrelation is a sum of exponentials for a polydisperse system
Particle Size Distribution
2
2


 
dGGqg ii
n
i
i )exp()()exp()(),(
1
1


• Cumulant analysis (assumes a Gaussian distribution of diffusion rates)
inverse problem
2nd order cumulant fit
mean decay rate
2nd order polydispersity index






 ...
!3!2
1)exp(),( 33221




qg
• Regularization
• fit the distribution of exponentials to obtain an approximation of the real
distribution assuming it is smooth
• particle sizes should differ by at least a factor of 5 to be seen as distinct

33. SLS of PAA/Chitosan PECs
Amine/Acid < 1.0, pH = 2.2, [Citric Acid] = 0.7 %
RG
1/Mw
Amine/Acid = 0.22 Amine/Acid = 0.45
Amine/Acid = 0.67 Amine/Acid = 0.92

34. R=0.25 Chitosan/PAA PECs on Glass
Topography
Phase
1 µm
0 µm
0.5 µm
1 µm0 µm 0.5 µm
10.917 V
18.827 V
500 nm
0 nm
250 nm
500 nm0 nm 250 nm
10.958 V
18.599 V
1 µm
0 µm
0.5 µm
1 µm0 µm 0.5 µm
0.00 nm
20.36 nm
500 nm
0 nm
250 nm
500 nm0 nm 250 nm
0.00 nm
21.39 nm

35. R=0.25 Chitosan/PAA PECs on Glass
Exit
Hori Vert Var
Enlarge Image
Line 2:
Line 1:
Line 3:
Line No.:
Line Type:
55
81
108
Distance
ZData
0
5.3
10.5
15.8
21 nm
0 0.2 0.4 0.6 0.8 1 µm
File Information:
Zmax: 20.4 nmZmin: 0.0 nm Scan Range: 1 µm
Result:
Point1:
Point2:
Diff:
Pt Angle:
Line1 Line2 Line3
Length:
Resolution: 256 x 256
Line Width
65 pts
PEC diameter: 50 nm, height: 10-15 nm

36. Chitosan/PAA Adsorbed Layer Compositions Vary With R. Acid Groups
of PAA Are Protonated – Consistent With Low pH of Solution.
Samples from Static Light Scattering study. Adsorption Time on Ge Surface = 5 minutes.