II. FLUID INTERFACES AND CAPILLARITY

Transcription

1 CONTENTS Preface vii I. INTRODUCTION 1 A. Interfaces 1 B. Colloids 4 C. The bridge to nanoscience What is nanoscience? Nanostructures and assemblies Generic nanoscience New tools of generic nanoscience The plan 22 II. FLUID INTERFACES AND CAPILLARITY 23 A. Fluid interfaces: Young s membrane model The thinness of interfaces Definition of surface tension 25 B. The surface tension of liquids Pure liquids Temperature dependence of surface tension Surface tension of solutions 29 C. Intermolecular forces and the origin of surface tension Van der Waals forces Surface tension as unbalanced intermolecular forces; the Hamaker constant Pressure deficit in the interfacial layer; Bakker s equation Components of the surface tension 41 D. Interfacial tension Experimental interfacial tension Combining rules for interfacial tension 43 E. Dynamic surface tension 46 F. Capillary hydrostatics: the Young-Laplace Equation Capillary pressure: pressure jump across a curved fluid interface The curvature of a surface Derivation of the Young-Laplace equation Boundary conditions for the Young-Laplace equation 55 G. Some solutions to the Young-Laplace equation Cylindrical surfaces; meniscus against a flat plate Axisymmetric and other surfaces 59

2 x CONTENTS 3. Nondimensionalization of the Young-Laplace equation; the Bond number Saddle-shaped surfaces 62 H. The measurement of surface and interfacial tension Geometric vs. force methods Capillary rise Sessile drop and pendant drop Du Noüy ring detachment Wilhelmy slide Langmuir film balance Drop weight (or volume) Maximum bubble pressure and dynamic surface tension The pulsating bubble surfactometer Elliptical (vibrating) jet Contracting circular jet Problems with interfacial tension measurement Spinning drop method 76 I. Forces on solids in contact with liquids: capillary interactions Liquid bridges Shared menisci 80 J. Effect of curvature on the equilibrium properties of bulk liquids: the Kelvin Effect The vapor pressure of small droplets and liquids in pores The effect of curvature on boiling point Capillary condensation Nucleation 88 K. Thin liquid films Disjoining pressure and its measurement The molecular origin of disjoining pressure The disjoining pressure isotherm The augmented Young-Laplace equation 101 SOME FUN THINGS TO DO: CHAPTER III. THERMODYNAMICS OF INTERFACIAL SYSTEMS 107 A. The thermodynamics of simple bulk systems Thermodynamic concepts The simple compressible system 108 B. The simple capillary system The work of extension Heat effects; abstract properties; definition of boundary tension 111 C. Extension to fluid-solid interfacial systems The work of area extension in fluid-solid systems Compound interfacial systems; Young s equation 116 D. Multicomponent interfacial systems The Gibbs dividing surface and adsorption 119

3 CONTENTS xi 2. Immiscible interfacial systems The measurement of adsorption The phase rule; descriptive equations for binary interfacial systems 127 E. The Gibbs adsorption equation 128 F. Surface tension of solutions Ideal-dilute capillary systems Moderately dilute capillary systems 135 G. Surface active agents (surfactants) and their solutions The structure of different types of surface active agents Solutions of non-electrolyte surfactants Solutions of electrolyte surfactants 147 H. Self-assembly of surfactant monomers in solution Formation of micelles: critical micelle concentration (CMC) Solubilization 160 I. Micelle morphology, other self-assembled structures, and concentrated surfactant solutions Micellar shape and the Critical Packing Parameter (CPP) Beyond micelles: other self-assembled structures Concentrated surfactant solutions; liquid crystalline mesophases Kinetics of micellization and other self-assembly processes 171 J. Dynamic surface tension of surfactant solutions Diffusion-controlled adsorption Finite adsorption-desorption kinetics 175 K. Insoluble (Langmuir) monolayers Formation of monolayers by spontaneous spreading Hydrodynamic consequences of monolayers: Gibbs elasticity π-a isotherms of insoluble monolayers Langmuir-Blodgett films Transport properties of monolayers 184 L. The thermodynamics of fluid-solid interfacial systems revisited The concept of interfacial energy and its measurement in fluid-solid systems Adsorption of non-polymeric molecules at the solid-liquid interface Experimental measurement of small molecule solid-liquid adsorption Adsorption of polymers at the solid-liquid interface 202 SOME FUN THINGS TO DO: CHAPTER IV. SOLID-LIQUID INTERACTIONS 214 A. Wettability and the contact angle: Young's Equation Importance of wetting; definition of contact angle 214

4 xii CONTENTS 2. Young s equation revisited; classification of wetting and contact angle values 216 B. Contact angle hysteresis Origins of hysteresis: roughness and heterogeneity Complexity of real surfaces: texture and scale Wenzel equation for rough surfaces Cassie-Baxter analysis of heterogeneous surfaces; composite surfaces and ultra-hydrophobicity The dynamic contact angle; Tanner s law 227 C. Methods for measuring the contact angle Optical or profile methods: contact angle goniometry Force methods: contact angle tensiometry Dynamic contact angle measurement 235 D. Relation of wetting behavior to surface chemical constitution Zisman plots; the critical surface tension The wettability series Estimates of surface energies from contact angle data or vice versa Thermodynamics of solid-liquid contact: work of adhesion, work of wetting and work of spreading; the Young-Dupré equation The promotion or retardation of wetting: practical strategies 245 E. Spreading of liquids on solid surfaces Criteria for spontaneous spreading; spreading morphology Temperature effects of wetting; heats of immersion and wetting transitions The kinetics of spreading on smooth surfaces Spreading agents; superspreaders 257 F. The relationship of wetting and spreading behavior to adhesion Definition of adhesion; adhesion mechanisms The Laws of Molecular Adhesion Practical adhesion vs. thermodynamic adhesion The importance of wetting (contact angle) to practical adhesion The optimization of thermodynamic contact adhesion Acid-base effects in adhesion Contact mechanics; the JKR method 272 G. Heterogeneous nucleation 277 H. Processes based on wettability changes or differences Detergency Flotation Selective or spherical agglomeration Offset lithographic printing 282 I. Wicking flows (capillary action) and absorbency Wicking into a single capillary tube 284

5 CONTENTS xiii 2. Wicking in porous media Practical strategies for promoting absorbency Immiscible displacement Mercury porosimitry Motion of liquid threads Surface wicking; spreading over rough or porous surfaces 295 J. Particles at interfaces Particles at solid-fluid interfaces: effects on wetting and spreading The disposition of particles at fluid interfaces Particle-assisted wetting Pickering emulsions Armored bubbles and liquid marbles Janus particles and nanoparticles at fluid interfaces 306 K. The description of solid surfaces Solid surface roughness Fractal surfaces Surface texture Measurement of surface roughness and texture by stylus profilometry 314 L. Optical techniques for surface characterization Optical microscopy Optical profilometry Confocal microscopy Electron microscopy Near-field scanning optical microscopy (NSOM) 320 M. Scanning probe microscopy (SPM) Scanning Tunneling Microscopy (STM) Atomic Force Microscopy (AFM) 324 N. Surface area of powders, pore size distribution 331 O. Energetic characterization of solid surfaces: Inverse Gas Chromatography (IGC) 333 SOME FUN THINGS TO DO: CHAPTER V. COLLOIDAL SYSTEMS: PHENOMENOLOGY AND CHARACTERIZATION 345 A. Preliminaries Definition and classification of colloids General properties of colloidal dispersions Dense vs. dilute dispersions 349 B. Mechanisms of lyophobic colloid instability Phase segregation: the "phoretic processes" Thermodynamic criteria for stability Aggregation Coalescence Particle size disproportionation 356

6 xiv CONTENTS C. Preparation of colloid particles and colloidal dispersions Classification of preparation strategies for lyophobic colloids Top-down strategies Bottom-up strategies 365 D. Morphology of colloids: particle size, size distribution, and particle shape Description of particle size distributions Distributions based on different size variables and weighting factors Normal (Gaussian) and log-normal distributions Particle shape 382 E. Sedimentation and centrifugation Individual particle settling: Stokes law Multi-particle, wall and charge effects on sedimentation Differential sedimentation; particle size analysis Centrifugation 395 F. Brownian motion; sedimentation-diffusion equilibrium Kinetic theory and diffusion Brownian motion Sedimentation (centrifugation) diffusion equilibrium Practical retrospective regarding sedimentation and other phoretic processes 407 G. Measurement of particle size and size distribution: overview Classification of methods Microscopy 410 H. Light scattering Classical (static) light scattering Rayleigh scattering Turbidity Rayleigh-Gans-Debye (RGD) scattering Mie scattering Fraunhofer diffraction; laser diffraction Inelastic scattering: absorbance; the Raman effect Scattering from denser dispersions Dynamic Light Scattering (Photon Correlation Spectroscopy) Dynamic light scattering from denser dispersions 442 I. Aperture, chromatographic and acoustic methods for particle sizing Aperture (one-at-a-time) methods Chromatographic methods Acoustic methods 448 SOME FUN THINGS TO DO: CHAPTER 5 450

7 CONTENTS xv VI. ELECTRICAL PROPERTIES OF INTERFACES 455 A. Origin of charge separation at interfaces Overview Preferential adsorption/desorption of lattice ions Specific adsorption of charged species Ionization of surface functional groups Isomorphic substitution Accumulation/depletion of electrons Interface charging in non-aqueous systems 463 B. Electric double layer formation and structure The Helmholtz model; electrostatic units The Gouy-Chapman model; Poisson-Boltzmann equation Boundary conditions to the Poisson-Boltzmann equation Double layers at spherical and cylindrical surfaces The free energy of double layer formation The Stern model; structure of the inner part of the double layer The mercury solution interface; electrocapillarity and refinements to the double layer model Oriented dipoles at the interface: the χ-potential 485 C. Electrostatic characterization of colloids by titration methods Colloid titrations Potentiometric titrations Conductometric titrations Donnan equilibrium and the suspension effect 493 D. Electrokinetics The electrokinetic phenomena The zeta potential and its interpretation Electrokinetic measurements; micro-electrophoresis Relationship of zeta potential to electrophoretic mobility Electrokinetic titrations Electro-acoustic measurements 514 E. Dielectrophoresis and optical trapping Dielectrophoresis Electrorotation and traveling wave dielectrophoresis Optical trapping; laser tweezers 520 SOME FUN THINGS TO DO: CHAPTER VII. INTERACTION BETWEEN COLLOID PARTICLES 525 A. Overview and rationale 525 B. Long-range van der Waals interactions The Hamaker (microscopic) approach Retardation The Lifshitz (macroscopic) approach Measurement of Hamaker constants 535 C. Electrostatic interactions; DLVO theory 540

8 xvi CONTENTS 1. Electrostatic repulsion between charged flat plates Electrostatic interactions between curved surfaces; the Derjaguin approximation DLVO theory: electrocratic dispersions Jar testing, the Schulze-Hardy rule and agreement with theory The Hofmeister series; ion speciation and ionic specific adsorption Repeptization Interaction between dissimilar surfaces: hetero-aggregation 558 D. Kinetics of aggregation Classification of aggregation rate processes and nomenclature Smoluchowski theory of diffusion-limited aggregation The hydrodynamic drainage effect Orthokinetic (shear flow induced) aggregation Reaction-limited (slow) aggregation; the stability ratio W Secondary minimum effects Kinetics of hetero-aggregation Measurement of early-stage aggregation kinetics (W) Surface aggregation Electrostatic stabilization and aggregation rates in apolar media 579 E. Steric stabilization and other colloid-polymer interactions Polymer adsorption and steric stabilization Thermodynamic considerations: enthalpic vs. entropic effects Fischer theory Steric repulsion plotted on DLVO coordinates Electro-steric stabilization Bridging flocculation Depletion flocculation Electrophoretic displays; electronic paper 599 F. The kinetics (and thermodynamics) of flocculation 601 G. Other non-dlvo interaction forces 603 H. Aggregate structure evolution; fractal aggregates Stages of the aggregation process Fractal aggregates The effect of particle size on aggregation phenomena; coating by nanoparticles 612 SOME FUN THINGS TO DO: CHAPTER 7 613

9 CONTENTS xvii VIII. RHEOLOGY OF DISPERSIONS 616 A. Rheology: scope and definitions 616 B. Viscometry Newton s law of viscosity Measurement of viscosity 618 C. The viscosity of colloidal dispersions Dilute dispersions; Einstein theory Denser dispersions of non-interacting particles Dilute dispersions of non-spherical particles 625 D. Non-Newtonian rheology General viscous behavior of dispersions of non-interacting particulates Fluids with a yield stress Time-dependent rheology Viscoelasticity 633 E. Electroviscous effects 637 SOME FUN THINGS TO DO: CHAPTER IX. EMULSIONS AND FOAMS 643 A. General consideration of emulsions Classification of emulsions Emulsifiers and emulsion stability Thermodynamics of emulsification/breakdown Preparation of emulsions 651 B. O/W or W/O emulsions? Rules of thumb The hydrophile-lipophile balance (HLB) and related scales Double (or multiple) emulsions 659 C. Application of emulsions Formation/breaking in situ Demulsification 663 D. Microemulsions Distinction between microemulsions and macro emulsions Phase behavior of microemulsion systems Ultra-low interfacial tension Interfacial film properties in microemulsion systems 672 E. General consideration of foams Nature and preparation of foams Stages in foam lifetime Stability mechanisms Foam behavior and foaming agents Antifoam action Froth flotation 686

10 xviii CONTENTS 7. Foaming in non-aqueous media; general surface activity near a phase split 687 SOME FUN THINGS TO DO: CHAPTER X. INTERFACIAL HYDRODYNAMICS 695 A. Unbalanced forces at fluid interfaces Unbalanced normal forces Tangential force imbalances: the Marangoni effect Boundary conditions at a fluid interface 702 B. Examples of Interfacial Hydrodynamic Flows The breakup of capillary jets Steady thermocapillary flow The motion of bubbles or drops in a temperature gradient Marangoni instability in a shallow liquid pool Bénard cells 718 C. Some Practical Implications of the Marangoni Effect Marangoni effects on mass transfer Marangoni drying Marangoni patterning 733 D. The Effect of Surface Active Agents Gibbs elasticity The boundary conditions describing the effects of surfactants The effect of surfactants on bubble or droplet circulation The effect of surfactants on the stability of a pool heated from below 745 SOME FUN THINGS TO DO: CHAPTER Appendix 1: EXERCISES 753 Appendix 2: THE TOP TEN 767 Appendix 3: OTHER SOURCES 771 Index 773