Physics and Chemistry of Interfaces

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1 Hans Jürgen Butt, Karlheinz Graf, and Michael Kappl Physics and Chemistry of Interfaces Second, Revised and Enlarged Edition WILEY- VCH WILEY-VCH Verlag GmbH & Co. KGaA

Contents Preface XI 1 Introduction 1 2 Liquid surfaces 5 2.1 Microscopic picture of the liquid surface 5 2.2 Surface tension 6 2.3 Equation of Young and Laplace 9 2.3.1 Curved liquid surfaces 9 2.3.2 Derivation of the Young-Laplace equation 11 2.

2 Contents Preface XI 1 Introduction 1 2 Liquid surfaces Microscopic picture of the liquid surface Surface tension Equation of Young and Laplace Curved liquid surfaces Derivation of the Young-Laplace equation Applying the Young-Laplace equation Techniques to measure the surface tension The Kelvin equation Capillary condensation Nucleation theory Summary Exercises 26 3 Thermodynamics of interfaces The surface excess Fundamental thermodynamic relations Internal energy and Helmholtz energy Equilibrium conditions Location of the interface Gibbs energy and definition of the surface tension Helmholtz surface energy, interfacial enthalpy, and Gibbs surface energy The surface tension of pure liquids Gibbs adsorption isotherm Derivation System of twocomponents Experimental aspects The Marangoni effect Summary Exercises 44 Physics and Chemistry of Interfaces. Second, Revised and Enlarged Edition. Hans-Jürgen Butt, Karlheinz Graf, Michael Kappl Copyright 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN:

VI Contents 4 The electric double layer 45 4.1 Introduction 45 4.2 Poisson-Boltzmann theory of the diffuse double layer 46 4.2.1 The Poisson-Boltzmann equation 46 4.2.2 Planar surfaces 47 4.2.3 The füll one-dimensional case 49 4.

3 VI Contents 4 The electric double layer Introduction Poisson-Boltzmann theory of the diffuse double layer The Poisson-Boltzmann equation Planar surfaces The füll one-dimensional case The Grahame equation Capacityof the diffuse electric double layer Beyond Poisson-Boltzmann theory Limitations of the Poisson-Boltzmann theory The Stern layer The Gibbs free energy of the electric double layer Summary Exercises 59 5 Effects at charged interfaces Electrocapillarity Theory Measurement of electrocapillarity Examples of charged surfaces Mercury Silveriodide Oxides Mica Semiconductors Measuring surface charge densities Potentiometrie colloid titration Capacitances Electrokinetic phenomena: The zeta potential The Navier-Stokes equation Electro-osmosis and Streaming potential Electrophoresis and Sedimentation potential Types of potentials Summary Exercises 84 6 Surface forces Van der Waals forces between molecules The van der Waals force between macroscopic solids Microscopic approach Macroscopic calculation Lifshitz theory Surface energy and Hamaker constant Concepts for the description of surface forces The Derjaguin approximation The disjoining pressure Measurement of surface forces 101

Contents VII 6.5 The electrostatic double-layer force 103 6.5.1 General equations 103 6.5.2 Electrostatic interaction between two identical surfaces 106 6.5.3 The DLVO theory 108 6.

4 Contents VII 6.5 The electrostatic double-layer force General equations Electrostatic interaction between two identical surfaces The DLVO theory Beyond DLVO theory The solvation force and confined liquids Non DLVO forces in an aqueous medium Steric and depletion interaction Properties of polymers Force between polymer coated surfaces Depletion forces Spherical particles in contact Summary Exercises Contact angle phenomena and wetting Young's equation The contact angle Derivation The line tension Complete wetting and wetting transitions Important wetting geometries Capillary rise Particles in the liquid-gas interface Network offibers Measurement of the contact angle Experimental methods Hysteresis in contact angle measurements Surface roughness and heterogeneity Theoretical aspects of contact angle phenomena Dynamics of wetting and dewetting Wetting Dewetting Applications Flotation Detergency Microfiuidics Adjustable wetting Summary Exercises Solid surfaces Introduction Description of crystalline surfaces The Substrate structure 154

VIII Contents 8.2.2 Surface relaxation and reconstruction 155 8.2.3 Description of adsorbate structures 158 8.3 Preparation of clean surfaces 158 8.4 Thermodynamics of solid surfaces 161 8.4.1 Surface stress and surface tension 161 8.

5 VIII Contents Surface relaxation and reconstruction Description of adsorbate structures Preparation of clean surfaces Thermodynamics of solid surfaces Surface stress and surface tension Determination of the surface energy Surface steps and defects Solid-solid interfaces Microscopy of solid surfaces Optical microscopy Electron microscopy Scanning probe microscopy Diffraction methods Diffraction patterns of two-dimensional periodic structures Diffraction with electrons, X-rays, and atoms Spectroscopic methods Spectroscopy using mainly inner electrons Spectroscopy with outer electrons Secondary ion mass spectrometry Summary Exercises Adsorption Introduction Defmitions The adsorption time Classification of adsorption isotherms Presentation of adsorption isotherms Thermodynamics of adsorption Heats of adsorption Differential quantities of adsorption and experimental results Adsorption modeis The Langmuir adsorption isotherm The Langmuir constant and the Gibbs energy of adsorption Langmuir adsorption with lateral interactions The BET adsorption isotherm Adsorption on heterogeneous surfaces The potential theory of Polanyi Experimental aspects of adsorption from the gas phase Measurement of adsorption isotherms Procedures to measure the specific surface area Adsorption on porous solids hysteresis Special aspects of chemisorption Adsorption from Solution Summary Exercises 217

Contents IX 10 Surface modiflcation 219 10.1 Introduction 219 10.2 Chemical vapor deposition 220 10.3 Soft matter deposition 222 10.3.1 Self-assembled monolayers 222 10.3.2 Physisorption of Polymers 226 10.

6 Contents IX 10 Surface modiflcation Introduction Chemical vapor deposition Soft matter deposition Self-assembled monolayers Physisorption of Polymers Polymerization on surfaces Plasma polymerization Etching techniques Lithography Summary Exercises Friction, lubrication, and wear Friction Introduction Amontons'and Coulomb's Law Static, kinetic, and stick-slip friction Rolling friction Friction and adhesion Experimental Aspects Techniques to measure friction Macroscopic friction Microscopic friction Lubrication Hydrodynamic lubrication Boundary lubrication Thin film lubrication Lubricants Wear : Summary Exercises Surfactants, micelles, emulsions, and foams Surfactants Spherical micelles, cylinders, and bilayers The critical micelle concentration Influence of temperature Thermodynamics of micellization Structure of Surfactant aggregates Biological membranes Macroemulsions General properties Formation Stabilization 282

X Contents 12.3.4 Evolution and aging 285 12.3.5 Coalescence and demulsification 287 12.4 Microemulsions 287 12.4.1 Sizeofdroplets 288 12.4.2 Elastic properties of Surfactant films 289 12.4.3 Factors influencing the structure of microemulsions 290 12.

7 X Contents Evolution and aging Coalescence and demulsification Microemulsions Sizeofdroplets Elastic properties of Surfactant films Factors influencing the structure of microemulsions Foams Classification, application and formation Structure of foams Soap films Evolution of foams Summary Exercises Thin films on surfaces of liquids Introduction Phases of monomolecular films Experimental techniques to study monolayers Optical methods X-ray reflection and diffraction The surface potential Surface elasticity and viscosity Langmuir-Blodgett transfer Thick films - spreading of one liquid on another Summary Exercises Solutions to exercises 321 Appendix A Analysis of diffraction patterns 343 A.l Diffraction at three dimensional crystals 343 A.l.l Bragg condition 343 A.1.2 Laue condition 344 A.1.3 The reciprocal lattice 345 A.1.4 Ewald construction 347 A.2 Diffraction at Surfaces 347 A.3 Intensity of diffraction peaks 349 B Symbols and abbreviations 353 Bibliography 357 Index 379

Contents. Preface XI Symbols and Abbreviations XIII. 1 Introduction 1

Contents. Preface XI Symbols and Abbreviations XIII. 1 Introduction 1 V Contents Preface XI Symbols and Abbreviations XIII 1 Introduction 1 2 Van der Waals Forces 5 2.1 Van der Waals Forces Between Molecules 5 2.1.1 Coulomb Interaction 5 2.1.2 Monopole Dipole Interaction