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

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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?

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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

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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.

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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

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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

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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?

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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.

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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

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*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

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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 !

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CloroxS&D Division & AOCS

You – The Audience and Consumer !

Appendix

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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

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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

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387 ± 7 ng/cm2

229 ± 4 ng/cm2

Total Polymer Concentration = 1.5 mM, pH =11.0, 20mM NaCl

Start Water Rinse

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• Autocorrelation is a sum of exponentials for a polydisperse system

Particle Size Distribution

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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

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Distance

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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.