Quantifying Adsorption of Surfactants and Polyelectrolyte Complexes at the Solid-Liquid Interface by Quartz Crystal Microgravimetry with Dissipation (QCM-D)
Mona M. KnockAdvanced Measurements Sciences
Mike Kinsinger, David R. ScheuingAdvanced TechnologyClorox Technical Center, Pleasanton CAANA 1.1 / S&D 1.2 #42420; May 2, 2011
Phase Behavior and Characterization of Polyelectrolyte Complexes (PECs)
AOCS Meeting – May, 2014D.R. Scheuing, Mona M. KnockCloroxS&D 3.0 – General Surfactants
Outline
What Are PECs & How To Make Them
What Can PECs Do?
Characterization of PECs in Solution
Characterization of PECs on Surfaces
2
PECs Are Self-Assembling Aggregates of Oppositely Charged Polymers
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Ladder – Molecular Level
orScrambled Egg - Multiple Chains in Particle
Ref. 1,2,6
Driving Force – Entropy Gain From Release of Small Counterions
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
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 SystemsHigh 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
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
Characterization of PECs in Solution
7
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.
*
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 ?
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50.0
500.0k
1.0M
1.5M
2.0M
2.5M
3.0M
3.5M
4.0M
Mw (
g/m
ole)
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 %
Dynamic Light Scattering Measures the Correlation Curve – Size is Calculated
11
212 )],([1),( qgqg
)exp(),(1 qg
tDq2
Monodisperse particles
Fit Exp
onential D
ecay F
unction
Decay rateDiffusion 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 MeasuredIf 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
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Velocity of Particles in Field Measured – Zeta Potential is Calculated
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Electrophoretic Mobility – Velocity of Particle
Henry’s function – approximately = 1.5
Viscosity Dielectric 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
**
Size Distributions of DADMAC/PAA PECs From DLS Show Shifts with R (DADMAC cationic equivalents/PAA acid equivalents)
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0
5
10
15
20
0.1 1 10 100 1000 10000
Inte
nsity
(P
erce
nt)
Size (d.nm)
Size Distribution by Intensity
Record 4: DAD/PAA R=0.25 No FWA 3 Record 10: DAD/PAA R=0.75 No FWA 3Record 12: DAD/PAA R=1.0 No FWA 2 Record 19: DAD/PAA R=2.0 No FWA 3
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
DADMAC/PAA PECs Are “Living” Systems – Behavior Shifts As pH Is Decreased
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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 SizePDI < 0.25 for all samples
Zeta Potential of + or – 30 mV Stabilizes DADMAC/PAA PECs
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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
What Can PECs Do?
16
Surface Modification & Engineering
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
50 mm
Trough on Horizon rig
Commercial Optics Enable Controlled Exposure of a Ge Surface to PECs Solutions
2.5 mL trough
Harrick “Horizon”Horizontal ATR rig
Dry Nitrogen/Air Input
Images of “Horizon” from Harrick, Inc.
PECs Solution
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
FT-IR Band Shifts Indicate Water Uptake Swells Adsorbed DADMAC/PAA Layers – Polymer Chain Dynamics Persist
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Carboxylate Bands (PAA) Shift Due to Increase in Distance To DADMAC Quat Group “Counterion” 11. Water Uptake Obvious.
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
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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.
Net Cationic PECs Adsorb on Silica and Resist Rinsing with Brine
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NaCl Rinse
Water Rinse
Multiple Adsorption/Water Rinse
Initial Maximum Adsorption201 ± 26 ng/cm2
After NaCl Rinse133 ± 20 ng/cm2
Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl.Flow rate constant at 150 microliters/minute
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 Adsorption398 ± 43 ng/cm2
After Water Rinses235 ± 42 ng/cm2
After NaCl rinse146 ± 47 ng/cm2
Adsorbed Amounts of PECs Converge Only After Extensive Rinsing. Net Anionic PECs Differ in Chain Dynamics from Net Cationic PECs
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Sauerbrey relation was maintained for both samples !
Summary
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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.
Thanks !
27
CloroxS&D Division & AOCS
You – The Audience and Consumer !
Appendix
28
References
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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/polym30207624. Alexander V. Kabanov ,Victor A. Kabanov , Advanced Drug Delivery Reviews 30 (1998) 49–605. Haifa H. Hariri, Joseph B. Schlenoff, Macromolecules DOI: 10.1021/ma1012976. Katja Henzler,Bjorn Haupt,Karlheinz Lauterbach, Alexander Wittemann, Oleg Borisov, Matthias Baliauff J.AM.CHEM.
SOC. 2010, 132,3159-3167. G.Decher, M.Eckle, J.Schmitt,B.Struth, Current Opinion in Colloid Interface Science, 1998, 3 (1), 32-398. G.Decher, B.Lehr,K.Lowack,Y.Lvov,J.Schmitt Biosensors Bioelectronics 1994, 9:677-6849. 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)
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 hours135 ± 16 ng/cm2
Start Water Rinse
Extremely Rapid Initial Adsorption
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
• Autocorrelation is a sum of exponentials for a polydisperse system
Particle Size Distribution
22
dGGqg ii
n
ii )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!21)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
Amine/Acid = 0.5
sin²(theta/2)0.0 0.2 0.4 0.6 0.8
K*c
/R(t
het
a)
0.0
-72.0x10
-74.0x10
-76.0x10
-78.0x10
Amine/Acid = 0.75
sin²(theta/2)0.0 0.2 0.4 0.6 0.8
K*c
/R(t
het
a)
0.0
-72.0x10
-74.0x10
-76.0x10
-78.0x10
-61.0x10
-61.2x10
Amine/Acid = 1.0
sin²(theta/2)0.0 0.2 0.4 0.6 0.8
K*c
/R(t
het
a)
0.0
-72.0x10
-74.0x10
-76.0x10
-78.0x10
-61.0x10
SLS of PAA/Chitosan PECs Amine/Acid < 1.0, pH = 2.2, [Citric Acid] = 0.7 %
Amine/Acid = 0.25
sin²(theta/2)0.0 0.2 0.4 0.6 0.8
K*c
/R(t
het
a)
0.0
-71.0x10
-72.0x10
-73.0x10
-74.0x10
-75.0x10
-76.0x10
RG
1/Mw
Amine/Acid = 0.22 Amine/Acid = 0.45
Amine/Acid = 0.67 Amine/Acid = 0.92
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 V500 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 nm500 nm
0 nm
250 nm
500 nm0 nm 250 nm
0.00 nm
21.39 nm
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
Z D
ata
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
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.
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