wennerstroem overbeek lecture in budapest 2006.pdf
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ELECTROSTATIC INTERACTIONS
Applications in colloid scienceOverbeek Medal Lecture
Håkan WennerströmDivision of Physical Chemistry 1Lund University
Combine theory and experiment.Study model systems that can illustrate theory.Combine molecular, colloidal and thermodynamic perspective.Demonstrate relevance for some applications.
Strategy
MotivationElectrostatic intermolecular interactionsare the most important cause of molecularorganization and selectivity inbiological and colloidal systems
Counterion NMR
Söderman,Engström&HW J.Colloid.Interfacce Sci 1980
Approach:Measure quadrupolar splittingsfor lamellar liquid crystals
23Na
7Li
Na+ vs Li+
competition
Question:How are counterions interactingwith highly charged surfaces?
The Poisson-Boltzmann equation andthe cell model
HW,Jönsson,Linse J.Chem. Phys.1982
Ael = 12 ρΦdV − k ci∫ (lnci −1)dV − ni{ln(ni /V ) −1}dV
i∑∫
ε0εr∇2Φ = −e zi
i∑ ci0 exp(−zieΦ /kT)
Force /area = kT cii∑ (zw ) −σ w /(2ε0εr)
Contac value theorem:
Poisson-Boltzmann equation
Mean field free energy functional
Minimization leads to:Cell model
Ionic amphiphiles 1Question:What is the electrostaticcontribution to the formation ofa micelle?
Approach: Solvethe PB equation.
Theory and experiment forCMC ofalkyl sulfates
Gunnarsson, Jönsson,HWJ.Phys.Chem 1980
Ionic ampiphiles 2
Gunnarsson, Jönsson,HWJ.Phys.Chem 1980
Q:Micelle-micelle interactions?
A:PB equation.Cell model.Test for ion chemical potential.
Theory and experimentFor SDS
Calculated phasediagram!
Ionic amphiphiles 3
Jönsson,HW J.Phys Chem 1987
Q:Is phase behavior driven by electrostatics?A:Create model free energy.
Ion Correlations 1
Guldbrand,Jönsson,HW,Linse J.Chem.Phys. 1984
Q:Accuracy of mean fieldapproximation?
A:MC simulations!
Model:Planar charged walls.Only counterions
MC
PB
Complete breakdownof PB for high charge densities and high counterion valencies
Non-monotonicforce curvein transition region
Ion correlations 2
Khan,Jönsson,HW J.Phys.Chem 1985
Q:Experimental manifestationof correlation attraction?
A:Compare lamellar liquid crystals with monovalent anddivalent counterions!
NaAOT - CaAOT-water
Observations:Pure Na system swellPure Ca system no swellingCoexistence at intermediatemixing.Generic behavior.
Ion correlations 3
Guldbrand,Nilsson, Nordensköld, J.Chem.Phys 1986
Q:Is geometry importantfor attraction?
A:MC simulation onDNA-like system.
Result:Attraction also incylindrical systems.Less pronounced.
PB
MC
Ion correlations 4
Jönsson,HW,Nonat,Cabane Langmuir 2004
Q:Practical applicationof correlation attraction
A:Cohesion in cement
In wet cement “C3S”particles dissolve andcharged silica-sulfatenanoparticles precipitate.pH increases steadily.
Ion correlations 5
Measured interparticle force.AFM
MC simulation for varyingcharge density.Jönsson,HW,Nonat,Cabane Langmuir 2004
Domain correlations
Tsao,Evans,HW Science 1993
Perkin,Kampf,Klein Phys.Rev.Lett 2006
ForceArea
≈ − σ 2
2εrε0
{exp[(κ 2 + 3.4 /R2)1
2 h /2]+ exp[−(κ 2 + 3.4 /R2)1
2 h /2]}−2
Attractionobserved for patchysurfaces
The dielectric approximation 1Q:Accuracy of the dielectricmodel of water?
A:Quantitative test ofMC simulations relativeto experimental phasediagram.
Theory appears towork quantitatively even for separations of 1nm!?
Turesson,Forsman,Åkesson,Jönsson,Langmuir 2004
Khan,Jönsson,HW J.Phys.Chem 1985
The dielectric approximation 2
Carlsson,Fogden,HW Langmuir 1999
Q:Temperature dependenceof electrostatic interactions?
Observation:The dielectricpermittivitty of water has anomalous T-dependence!Electrostatic free energylarger at high T.
Test: Ionic microemulsions
Non-ionicsystem
Ionic system
Full lines:calculation basedon PB equation andcell model
PB theory describestemperature dependencequantitativly!
The dielectric approximation 3Q:Attractive electrostaticinteractions at short range?
Proton NMR,alkyl chain and CH3
a)
b)
c)A:Hydration of DNA- CTA+
Leal,Topgaard,Martin,HWJ.Phys.Chem2004
The dielectric approximation 4
Leal,Wadsö,Olofsson,Miguel,HW J.Phys.Chem B 2004
A:Calorimetric study of of DNA- CTA+
Free energy Enthalpy
Q:Thermodynamics of hydration?
The dielectric approximation 5
Leal,Moniri,Pegado,HW Submitted
Q:Effect of salt?
A:Add NaCl to dry DNA- CTA+.
Result:Salt increases swelling.Effect can be modeled using PBequation
Dissolution ofNaCl in complex
Lifshitz theory and classical electrostatics 1
HW,Daicic,Ninham Phys.Rev.A 1999
OH
H
O
HH
R
V(R)=− 3kTα2
(4πε0)2R6
DispersionDebye andKeesom interactionshave an identicalasymptotic form forthe free energy!!!(but for energy)
Lifshitz theory and classical electrostatics 2
HW Collids&Surfaces A 2003h
Dipolarfluid
Dipolarfluid
G /area = − kT32πh2 x 2
0
∞
∫ {(ε(0) +1ε(0) −1
)2ex −1}−1dx
Comment: An elementary useof Lifshitz theory would suggesta different expression!
Unresolved issues
The breakdown of the dielectric approximationInteractions at short range, adhesion, binding constantsAnions at polar-apolar interfaceThe distance dependence of the hydrophobic interactionDipolar correlations in waterClassical-quantum high T free energy equivalence
Acknowledgements
Thanks toBengt Jönsson: A master of electrostatic theory and much moreBo Jönsson: For all computer simulation contributionsSven EngströmOlle SödermanAndrew FogdenIngemar CarlssonJohn DaicicAnd all collegues at Physical Chemistry 1, Lund University