Table Of Content

COLLOID AND INTERFACE SCIENCE PALLAB GHOSH Associate Professor Department of Chemical Engineering Indian Institute of Technology Guwahati New Delhi-110001 2009 About the cover illustration: The background depicts the waves created at the air–water interface induced by external forces (e.g. when a rain drop falls on a calm water surface); (top left) petroleum oil-spill on sea that can cause extensive environmental hazard; (middle) gas bubbles fascinate us with their shape and colour, and they also constitute an integral part of gas–liquid dispersions; (bottom right) water-drops on hydrophobic tree-leaves depicting the wetting phenomena; (top right) carbon-nanotube catalytic reactor depicting the production of ethanol [taken from the work of Pan, X., Fan, Z., Chen, W., Ding, Y., Luo, H. and Bao, X., “Enhanced Ethanol Production Inside Carbon-Nanotube Reactors Containing Catalytic Particles”, Nature Materials, 6, 507 (2007), reproduced by permission from Macmillan Publishers Ltd., © 2007] Rs. 425.00 COLLOID AND INTERFACE SCIENCE Pallab Ghosh © 2009 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-3857-9 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi-110001 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli-131028, Sonepat, Haryana. Contents Preface xi SI Units xiii 1. BASIC CONCEPTS OF COLLOIDS AND INTERFACES .....................................1–23 1.1 Introduction ..................................................................................................................................2 1.2 Examples of Interfacial Phenomena..............................................................................................3 1.2.1 Capillary Action..................................................................................................................3 1.2.2 Tears of Wine......................................................................................................................4 1.3 Solid–Fluid Interfaces...................................................................................................................5 1.4 Colloids ........................................................................................................................................6 1.4.1 Colloids and Interfaces .......................................................................................................7 1.4.2 Classification of Colloids....................................................................................................9 1.4.3 Electrical Charge on Colloid Particles..............................................................................10 1.4.4 Stability of Colloids..........................................................................................................11 1.4.5 Kinetic and Thermodynamic Stabilities............................................................................13 1.4.6 Preparation of Colloids.....................................................................................................13 1.4.7 Parameters of Colloid Dispersions....................................................................................17 Summary..............................................................................................................................................19 Keywords.............................................................................................................................................19 Notation...............................................................................................................................................20 Exercises .............................................................................................................................................21 Numerical and Analytical Problems...................................................................................................21 Further Reading..................................................................................................................................22 2. PROPERTIES OF COLLOID DISPERSIONS.......................................................24–68 2.1 Introduction ................................................................................................................................25 2.2 Sedimentation under Gravity......................................................................................................25 2.3 Sedimentation in a Centrifugal Field..........................................................................................28 (cid:2)(cid:2)(cid:2) (cid:2)(cid:3) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 2.4 Brownian Motion........................................................................................................................30 2.5 Osmotic Pressure........................................................................................................................32 2.6 Optical Properties.......................................................................................................................36 2.6.1 Determination of Molecular Weight by Light Scattering..................................................39 2.6.2 Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) .............................................................................42 2.6.3 Dynamic Light Scattering (DLS)......................................................................................42 2.6.4 Small-Angle Neutron Scattering (SANS).........................................................................43 2.7 Electrical Properties....................................................................................................................43 2.7.1 Reciprocal Relationships..................................................................................................48 2.7.2 (cid:2)-potential Obtained from Different Techniques...............................................................49 2.8 Some Properties of Lyophilic Sols..............................................................................................49 2.8.1 Hofmeister Series .............................................................................................................49 2.8.2 Viscosity of Lyophilic Sols...............................................................................................50 2.8.3 Gelation............................................................................................................................51 2.8.4 Imbibition.........................................................................................................................51 2.8.5 Syneresis...........................................................................................................................51 2.8.6 Gold Number....................................................................................................................52 2.9 Rheological Properties of Colloid Dispersions...........................................................................52 2.9.1 Einstein’s Equation of Viscosity .......................................................................................55 2.9.2 Mark–Houwink Equation for Polymer Solutions..............................................................56 2.9.3 Deborah Number ..............................................................................................................57 2.9.4 Peclet Number..................................................................................................................57 Summary..............................................................................................................................................58 Keywords.............................................................................................................................................59 Notation...............................................................................................................................................60 Exercises .............................................................................................................................................62 Numerical Problems............................................................................................................................63 Appendix..............................................................................................................................................66 Further Reading..................................................................................................................................66 3. SURFACTANTS AND THEIR PROPERTIES.......................................................69–94 3.1 Introduction ................................................................................................................................70 3.2 Surfactants and their Properties ..................................................................................................70 3.2.1 Anionic Surfactants.........................................................................................................71 3.2.2 Cationic Surfactants........................................................................................................72 3.2.3 Zwitterionic Surfactants..................................................................................................72 3.2.4 Nonionic Surfactants.......................................................................................................72 3.2.5 Gemini Surfactants..........................................................................................................73 3.2.6 Biosurfactants.................................................................................................................73 3.2.7 Micellisation of Surfactants............................................................................................74 3.2.8 Thermodynamics of Micellisation ..................................................................................83 3.2.9 Krafft Point and Cloud Point...........................................................................................84 3.2.10 Liquid Crystals................................................................................................................84 3.2.11 Hydrophilic–Lipophilic Balance.....................................................................................86 3.3 Emulsions and Microemulsions..................................................................................................88 3.4 Foams .........................................................................................................................................89 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:3) Summary..............................................................................................................................................90 Keywords.............................................................................................................................................90 Notation...............................................................................................................................................91 Exercises .............................................................................................................................................91 Numerical Problems............................................................................................................................92 Further Reading..................................................................................................................................93 4. SURFACE AND INTERFACIAL TENSION.........................................................95–142 4.1 Introduction ................................................................................................................................96 4.2 Surface Tension...........................................................................................................................96 4.2.1 Effect of Temperature on Surface Tension ....................................................................103 4.3 Interfacial Tension ....................................................................................................................106 4.4 Contact Angle and Wetting.......................................................................................................108 4.5 Shape of the Surfaces and Interfaces.........................................................................................109 4.5.1 Radius of Curvature......................................................................................................109 4.5.2 Young–Laplace Equation..............................................................................................112 4.5.3 Pendant and Sessile Drops............................................................................................115 4.5.4 Capillary Rise or Depression ........................................................................................118 4.5.5 The Kelvin Equation.....................................................................................................120 4.6 Measurement of Surface and Interfacial Tension......................................................................122 4.6.1 The Drop-Weight Method.............................................................................................122 4.6.2 du Noüy Ring Method ..................................................................................................124 4.6.3 Wilhelmy Plate Method................................................................................................126 4.6.4 Maximum Bubble Pressure Method..............................................................................127 4.6.5 Spinning-Drop Method.................................................................................................128 4.7 Measurement of Contact Angle ................................................................................................130 Summary............................................................................................................................................132 Keywords...........................................................................................................................................133 Notation.............................................................................................................................................134 Exercises ...........................................................................................................................................136 Numerical and Analytical Problems.................................................................................................137 Appendix............................................................................................................................................138 Further Reading................................................................................................................................140 5. INTERMOLECULAR AND SURFACE FORCES..............................................143–200 5.1 Introduction ..............................................................................................................................143 5.2 van der Waals Forces ................................................................................................................145 5.2.1 van der Waals Force between Two Macroscopic Bodies...............................................149 5.2.2 Derjaguin Approximation .............................................................................................151 5.2.3 The Hamaker Constant..................................................................................................152 5.2.4 Estimation of Surface Tension from Hamaker Constant ...............................................157 5.2.5 van der Waals Force in Electrolyte Solutions................................................................157 5.2.6 Disjoining Pressure.......................................................................................................158 5.2.7 Experimental Determination of van der Waals Force....................................................158 5.3 Electrostatic Double Layer Force .............................................................................................160 5.3.1 The Models of Electrostatic Double Layer ...................................................................162 5.3.2 Mathematical Modelling of the Diffuse Double Layer .................................................164 5.3.3 The Stern Layer ............................................................................................................171 5.3.4 Double Layer around Spherical Particles......................................................................173 (cid:3)(cid:2) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 5.3.5 Electrostatic Double Layer Repulsion between Two Surfaces......................................174 5.3.6 The Derjaguin Approximation ......................................................................................177 5.3.7 The Zeta Potential.........................................................................................................177 5.3.8 Limitations of the Poisson–Boltzmann Equation..........................................................179 5.4 The DLVO Theory....................................................................................................................180 5.5 Non-DLVO Forces....................................................................................................................184 5.5.1 Hydration Force............................................................................................................184 5.5.2 Hydrophobic Interaction...............................................................................................186 5.6 Steric Forces due to Adsorbed Polymer Molecules...................................................................186 Summary............................................................................................................................................188 Keywords...........................................................................................................................................189 Notation.............................................................................................................................................190 Exercises ...........................................................................................................................................192 Numerical and Analytical Problems.................................................................................................194 Appendix 5A......................................................................................................................................195 Appendix 5B......................................................................................................................................197 Further Reading................................................................................................................................198 6. ADSORPTION AT INTERFACES .....................................................................201–238 6.1 Introduction ..............................................................................................................................202 6.2 The Gibbs Dividing Surface .....................................................................................................202 6.3 Gibbs Adsorption Equation.......................................................................................................204 6.4 Langmuir and Frumkin Adsorption Isotherms..........................................................................207 6.5 Surface Equation of State (EOS) ..............................................................................................208 6.6 Effect of Salt on Adsorption of Surfactants...............................................................................210 6.7 Adsorption Isotherms Incorporating the Electrostatic Effects...................................................215 6.8 Calculation of Free Energy of Adsorption ................................................................................217 6.9 Adsorption of Inorganic Salts at Interfaces...............................................................................218 6.10 Dynamics of Adsorption of Surfactants at the Interface............................................................219 6.11 Adsorption at Solid–Fluid Interfaces........................................................................................221 6.11.1 Henry, Freundlich and Langmuir Adsorption Isotherms .............................................222 6.11.2 The Brunauer–Emmett–Teller (BET) Theory..............................................................224 6.11.3 Adsorption Hysteresis.................................................................................................226 6.12 Direct Experimental Techniques for Measurement of Adsorption ............................................228 Summary............................................................................................................................................229 Keywords...........................................................................................................................................229 Notation.............................................................................................................................................230 Exercises ...........................................................................................................................................232 Numerical and Analytical Problems.................................................................................................232 Appendix............................................................................................................................................235 Further Reading................................................................................................................................236 7. INTERFACIAL RHEOLOGY..............................................................................239–269 7.1 Introduction ..............................................................................................................................239 7.2 Surface Shear Viscosity ............................................................................................................240 7.2.1 Molecular Theory of Newtonian Surface Viscosity.......................................................242 7.2.2 Boussinesq Number......................................................................................................243 7.2.3 Measurement of Surface Shear Viscosity......................................................................243 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:3)(cid:2)(cid:2) 7.3 Interfacial Tension Gradient and Marangoni Effect..................................................................250 7.4 Surface Dilatational Viscosity...................................................................................................252 7.4.1 Measurement of Surface Dilatational Viscosity............................................................254 7.5 Boussinesq–Scriven Model.......................................................................................................257 7.6 Importance of (cid:3)S and (cid:4)S ............................................................................................................258 7.7 Interfacial Turbulence...............................................................................................................259 7.8 Motions of Drops in a Liquid....................................................................................................261 Summary............................................................................................................................................264 Keywords...........................................................................................................................................264 Notation.............................................................................................................................................264 Exercises ...........................................................................................................................................266 Numerical and Analytical Problems.................................................................................................266 Further Reading................................................................................................................................268 8. MONOLAYERS AND THIN LIQUID FILMS .....................................................270–315 8.1 Introduction ..............................................................................................................................271 8.2 Surfactant Monolayers and their Applications..........................................................................271 8.3 Properties of Monolayers..........................................................................................................272 8.3.1 Measurement of Surface Pressure.................................................................................273 8.3.2 Surface Pressure Isotherm.............................................................................................274 8.3.3 Model of Gas-Phase Monolayer....................................................................................276 8.3.4 Surface Potential...........................................................................................................278 8.3.5 Monolayers at Liquid–Liquid Interfaces.......................................................................279 8.4 Langmuir–Blodgett Films.........................................................................................................279 8.5 Surface Diffusion......................................................................................................................282 8.5.1 The Apparatus...............................................................................................................283 8.5.2 Measurement Procedure................................................................................................284 8.5.3 Determination of D ......................................................................................................285 s 8.6 Thin Liquid Films.....................................................................................................................286 8.6.1 Critical Film Thickness.................................................................................................287 8.6.2 Hydrostatics of Thin Liquid Films................................................................................292 8.6.3 Drainage of Liquid Films..............................................................................................293 8.6.4 The Lubrication Flow....................................................................................................295 8.6.5 Film-Drainage Time......................................................................................................298 8.6.6 Stability of Thin Liquid Films.......................................................................................302 8.6.7 Black Films...................................................................................................................303 Summary............................................................................................................................................306 Keywords...........................................................................................................................................307 Notation.............................................................................................................................................307 Exercises ...........................................................................................................................................309 Numerical and Analytical Problems.................................................................................................310 Appendix............................................................................................................................................311 Further Reading................................................................................................................................312 9. EMULSIONS, MICROEMULSIONS AND FOAMS ...........................................316–371 9.1 Introduction ..............................................................................................................................317 9.2 Emulsions.................................................................................................................................317 9.2.1 Preparation of Emulsions..............................................................................................318 (cid:3)(cid:2)(cid:2)(cid:2) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 9.2.2 Stability of Emulsions...................................................................................................319 9.2.3 Ostwald Ripening .........................................................................................................321 9.2.4 Flocculation and Coalescence of Drops........................................................................324 9.2.5 Phase Inversion.............................................................................................................338 9.2.6 Application of Emulsions..............................................................................................339 9.3 Microemulsions........................................................................................................................340 9.3.1 Winsor’s Classification of Microemulsions ..................................................................340 9.3.2 Stability of Microemulsions..........................................................................................345 9.3.3 Rheology of Microemulsions........................................................................................351 9.3.4 Applications of Microemulsions...................................................................................353 9.4 Foams .......................................................................................................................................353 9.4.1 Preparation of Foams and Measurement of their Stability............................................355 9.4.2 Structure of Foams........................................................................................................356 9.4.3 Foam Drainage..............................................................................................................358 9.4.4 Applications of Foams..................................................................................................360 Summary............................................................................................................................................360 Keywords...........................................................................................................................................361 Notation.............................................................................................................................................362 Exercises ...........................................................................................................................................364 Numerical and Analytical Problems.................................................................................................366 Further Reading................................................................................................................................368 10. BIOLOGICAL INTERFACES.............................................................................372–409 10.1 Introduction ..............................................................................................................................372 10.2 Protein Adsorption at Interfaces................................................................................................373 10.2.1 Adsorption of Proteins at Solid–Liquid Interfaces......................................................374 10.2.2 Adsorption of Proteins at Fluid–Fluid Interfaces........................................................377 10.3 Biological Membranes..............................................................................................................381 10.4 Interfacial Forces......................................................................................................................384 10.4.1 van der Waals Force....................................................................................................385 10.4.2 Hydration Force..........................................................................................................385 10.4.3 Steric Forces ...............................................................................................................387 10.4.4 Electrostatic Double Layer Force................................................................................390 10.4.5 Hydrophobic Forces....................................................................................................392 10.5 Cell Adhesion ...........................................................................................................................393 10.6 Pulmonary Surfactant ...............................................................................................................396 10.7 Biomaterials..............................................................................................................................398 Summary............................................................................................................................................400 Keywords...........................................................................................................................................401 Notation.............................................................................................................................................401 Exercises ...........................................................................................................................................403 Numerical and Analytical Problems.................................................................................................404 Appendix............................................................................................................................................405 Further Reading................................................................................................................................406 11. NANOMATERIALS ............................................................................................410–451 11.1 Introduction ..............................................................................................................................411 11.2 Approaches for the Synthesis of Nanomaterials .......................................................................412 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:2)(cid:4) 11.3 Self-Assembly and Structure ....................................................................................................412 11.4 Synthesis of Nanoparticles........................................................................................................414 11.4.1 Homogeneous Nucleation...........................................................................................414 11.4.2 Microemulsion-Based Methods..................................................................................421 11.4.3 Synthesis of Carbon Fullerenes...................................................................................422 11.5 Synthesis of Nanowires, Nanorods and Nanotubes...................................................................425 11.5.1 Nanowires and Nanorods............................................................................................425 11.5.2 Nanotubes...................................................................................................................429 11.6 Deposition of Thin Films..........................................................................................................435 11.7 Synthesis of Microporous and Mesoporous Materials..............................................................438 11.8 Lithographic Techniques...........................................................................................................442 11.9 Toxic Effects of Nanomaterials.................................................................................................444 Summary............................................................................................................................................445 Keywords...........................................................................................................................................445 Notation.............................................................................................................................................446 Exercises ...........................................................................................................................................446 Numerical and Analytical Problems.................................................................................................448 Further Reading................................................................................................................................448 12. INTERFACIAL REACTIONS .............................................................................452–493 12.1 Introduction ..............................................................................................................................452 12.2 Reactions at Solid–Fluid Interfaces ..........................................................................................453 12.2.1 Langmuir–Hinshelwood Model ..................................................................................455 12.2.2 External Transport Processes ......................................................................................460 12.2.3 Determination of Mass and Heat Transfer Coefficients ..............................................464 12.2.4 Internal Transport Processes .......................................................................................465 12.3 Interfacial Polycondensation.....................................................................................................469 12.4 Gas–Liquid and Liquid–Liquid Interfacial Reactions...............................................................476 12.5 Reactions at Biointerfaces ........................................................................................................477 12.6 Micellar Catalysis.....................................................................................................................481 12.7 Phase Transfer Catalysis...........................................................................................................484 Summary............................................................................................................................................485 Keywords...........................................................................................................................................486 Notation.............................................................................................................................................486 Exercises ...........................................................................................................................................489 Numerical and Analytical Problems.................................................................................................490 Further Reading................................................................................................................................492 INDEX .......................................................................................................................495–503

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COLLOID AND INTERFACE SCIENCE PALLAB GHOSH Associate Professor Department of Chemical Engineering Indian Institute of Technology Guwahati New Delhi-110001 2009 About the cover illustration: The background depicts the waves created at the air–water interface induced by external forces (e.g. when a rain drop falls on a calm water surface); (top left) petroleum oil-spill on sea that can cause extensive environmental hazard; (middle) gas bubbles fascinate us with their shape and colour, and they also constitute an integral part of gas–liquid dispersions; (bottom right) water-drops on hydrophobic tree-leaves depicting the wetting phenomena; (top right) carbon-nanotube catalytic reactor depicting the production of ethanol [taken from the work of Pan, X., Fan, Z., Chen, W., Ding, Y., Luo, H. and Bao, X., “Enhanced Ethanol Production Inside Carbon-Nanotube Reactors Containing Catalytic Particles”, Nature Materials, 6, 507 (2007), reproduced by permission from Macmillan Publishers Ltd., © 2007] Rs. 425.00 COLLOID AND INTERFACE SCIENCE Pallab Ghosh © 2009 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-3857-9 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi-110001 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli-131028, Sonepat, Haryana. Contents Preface xi SI Units xiii 1. BASIC CONCEPTS OF COLLOIDS AND INTERFACES .....................................1–23 1.1 Introduction ..................................................................................................................................2 1.2 Examples of Interfacial Phenomena..............................................................................................3 1.2.1 Capillary Action..................................................................................................................3 1.2.2 Tears of Wine......................................................................................................................4 1.3 Solid–Fluid Interfaces...................................................................................................................5 1.4 Colloids ........................................................................................................................................6 1.4.1 Colloids and Interfaces .......................................................................................................7 1.4.2 Classification of Colloids....................................................................................................9 1.4.3 Electrical Charge on Colloid Particles..............................................................................10 1.4.4 Stability of Colloids..........................................................................................................11 1.4.5 Kinetic and Thermodynamic Stabilities............................................................................13 1.4.6 Preparation of Colloids.....................................................................................................13 1.4.7 Parameters of Colloid Dispersions....................................................................................17 Summary..............................................................................................................................................19 Keywords.............................................................................................................................................19 Notation...............................................................................................................................................20 Exercises .............................................................................................................................................21 Numerical and Analytical Problems...................................................................................................21 Further Reading..................................................................................................................................22 2. PROPERTIES OF COLLOID DISPERSIONS.......................................................24–68 2.1 Introduction ................................................................................................................................25 2.2 Sedimentation under Gravity......................................................................................................25 2.3 Sedimentation in a Centrifugal Field..........................................................................................28 (cid:2)(cid:2)(cid:2) (cid:2)(cid:3) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 2.4 Brownian Motion........................................................................................................................30 2.5 Osmotic Pressure........................................................................................................................32 2.6 Optical Properties.......................................................................................................................36 2.6.1 Determination of Molecular Weight by Light Scattering..................................................39 2.6.2 Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) .............................................................................42 2.6.3 Dynamic Light Scattering (DLS)......................................................................................42 2.6.4 Small-Angle Neutron Scattering (SANS).........................................................................43 2.7 Electrical Properties....................................................................................................................43 2.7.1 Reciprocal Relationships..................................................................................................48 2.7.2 (cid:2)-potential Obtained from Different Techniques...............................................................49 2.8 Some Properties of Lyophilic Sols..............................................................................................49 2.8.1 Hofmeister Series .............................................................................................................49 2.8.2 Viscosity of Lyophilic Sols...............................................................................................50 2.8.3 Gelation............................................................................................................................51 2.8.4 Imbibition.........................................................................................................................51 2.8.5 Syneresis...........................................................................................................................51 2.8.6 Gold Number....................................................................................................................52 2.9 Rheological Properties of Colloid Dispersions...........................................................................52 2.9.1 Einstein’s Equation of Viscosity .......................................................................................55 2.9.2 Mark–Houwink Equation for Polymer Solutions..............................................................56 2.9.3 Deborah Number ..............................................................................................................57 2.9.4 Peclet Number..................................................................................................................57 Summary..............................................................................................................................................58 Keywords.............................................................................................................................................59 Notation...............................................................................................................................................60 Exercises .............................................................................................................................................62 Numerical Problems............................................................................................................................63 Appendix..............................................................................................................................................66 Further Reading..................................................................................................................................66 3. SURFACTANTS AND THEIR PROPERTIES.......................................................69–94 3.1 Introduction ................................................................................................................................70 3.2 Surfactants and their Properties ..................................................................................................70 3.2.1 Anionic Surfactants.........................................................................................................71 3.2.2 Cationic Surfactants........................................................................................................72 3.2.3 Zwitterionic Surfactants..................................................................................................72 3.2.4 Nonionic Surfactants.......................................................................................................72 3.2.5 Gemini Surfactants..........................................................................................................73 3.2.6 Biosurfactants.................................................................................................................73 3.2.7 Micellisation of Surfactants............................................................................................74 3.2.8 Thermodynamics of Micellisation ..................................................................................83 3.2.9 Krafft Point and Cloud Point...........................................................................................84 3.2.10 Liquid Crystals................................................................................................................84 3.2.11 Hydrophilic–Lipophilic Balance.....................................................................................86 3.3 Emulsions and Microemulsions..................................................................................................88 3.4 Foams .........................................................................................................................................89 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:3) Summary..............................................................................................................................................90 Keywords.............................................................................................................................................90 Notation...............................................................................................................................................91 Exercises .............................................................................................................................................91 Numerical Problems............................................................................................................................92 Further Reading..................................................................................................................................93 4. SURFACE AND INTERFACIAL TENSION.........................................................95–142 4.1 Introduction ................................................................................................................................96 4.2 Surface Tension...........................................................................................................................96 4.2.1 Effect of Temperature on Surface Tension ....................................................................103 4.3 Interfacial Tension ....................................................................................................................106 4.4 Contact Angle and Wetting.......................................................................................................108 4.5 Shape of the Surfaces and Interfaces.........................................................................................109 4.5.1 Radius of Curvature......................................................................................................109 4.5.2 Young–Laplace Equation..............................................................................................112 4.5.3 Pendant and Sessile Drops............................................................................................115 4.5.4 Capillary Rise or Depression ........................................................................................118 4.5.5 The Kelvin Equation.....................................................................................................120 4.6 Measurement of Surface and Interfacial Tension......................................................................122 4.6.1 The Drop-Weight Method.............................................................................................122 4.6.2 du Noüy Ring Method ..................................................................................................124 4.6.3 Wilhelmy Plate Method................................................................................................126 4.6.4 Maximum Bubble Pressure Method..............................................................................127 4.6.5 Spinning-Drop Method.................................................................................................128 4.7 Measurement of Contact Angle ................................................................................................130 Summary............................................................................................................................................132 Keywords...........................................................................................................................................133 Notation.............................................................................................................................................134 Exercises ...........................................................................................................................................136 Numerical and Analytical Problems.................................................................................................137 Appendix............................................................................................................................................138 Further Reading................................................................................................................................140 5. INTERMOLECULAR AND SURFACE FORCES..............................................143–200 5.1 Introduction ..............................................................................................................................143 5.2 van der Waals Forces ................................................................................................................145 5.2.1 van der Waals Force between Two Macroscopic Bodies...............................................149 5.2.2 Derjaguin Approximation .............................................................................................151 5.2.3 The Hamaker Constant..................................................................................................152 5.2.4 Estimation of Surface Tension from Hamaker Constant ...............................................157 5.2.5 van der Waals Force in Electrolyte Solutions................................................................157 5.2.6 Disjoining Pressure.......................................................................................................158 5.2.7 Experimental Determination of van der Waals Force....................................................158 5.3 Electrostatic Double Layer Force .............................................................................................160 5.3.1 The Models of Electrostatic Double Layer ...................................................................162 5.3.2 Mathematical Modelling of the Diffuse Double Layer .................................................164 5.3.3 The Stern Layer ............................................................................................................171 5.3.4 Double Layer around Spherical Particles......................................................................173 (cid:3)(cid:2) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 5.3.5 Electrostatic Double Layer Repulsion between Two Surfaces......................................174 5.3.6 The Derjaguin Approximation ......................................................................................177 5.3.7 The Zeta Potential.........................................................................................................177 5.3.8 Limitations of the Poisson–Boltzmann Equation..........................................................179 5.4 The DLVO Theory....................................................................................................................180 5.5 Non-DLVO Forces....................................................................................................................184 5.5.1 Hydration Force............................................................................................................184 5.5.2 Hydrophobic Interaction...............................................................................................186 5.6 Steric Forces due to Adsorbed Polymer Molecules...................................................................186 Summary............................................................................................................................................188 Keywords...........................................................................................................................................189 Notation.............................................................................................................................................190 Exercises ...........................................................................................................................................192 Numerical and Analytical Problems.................................................................................................194 Appendix 5A......................................................................................................................................195 Appendix 5B......................................................................................................................................197 Further Reading................................................................................................................................198 6. ADSORPTION AT INTERFACES .....................................................................201–238 6.1 Introduction ..............................................................................................................................202 6.2 The Gibbs Dividing Surface .....................................................................................................202 6.3 Gibbs Adsorption Equation.......................................................................................................204 6.4 Langmuir and Frumkin Adsorption Isotherms..........................................................................207 6.5 Surface Equation of State (EOS) ..............................................................................................208 6.6 Effect of Salt on Adsorption of Surfactants...............................................................................210 6.7 Adsorption Isotherms Incorporating the Electrostatic Effects...................................................215 6.8 Calculation of Free Energy of Adsorption ................................................................................217 6.9 Adsorption of Inorganic Salts at Interfaces...............................................................................218 6.10 Dynamics of Adsorption of Surfactants at the Interface............................................................219 6.11 Adsorption at Solid–Fluid Interfaces........................................................................................221 6.11.1 Henry, Freundlich and Langmuir Adsorption Isotherms .............................................222 6.11.2 The Brunauer–Emmett–Teller (BET) Theory..............................................................224 6.11.3 Adsorption Hysteresis.................................................................................................226 6.12 Direct Experimental Techniques for Measurement of Adsorption ............................................228 Summary............................................................................................................................................229 Keywords...........................................................................................................................................229 Notation.............................................................................................................................................230 Exercises ...........................................................................................................................................232 Numerical and Analytical Problems.................................................................................................232 Appendix............................................................................................................................................235 Further Reading................................................................................................................................236 7. INTERFACIAL RHEOLOGY..............................................................................239–269 7.1 Introduction ..............................................................................................................................239 7.2 Surface Shear Viscosity ............................................................................................................240 7.2.1 Molecular Theory of Newtonian Surface Viscosity.......................................................242 7.2.2 Boussinesq Number......................................................................................................243 7.2.3 Measurement of Surface Shear Viscosity......................................................................243 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:3)(cid:2)(cid:2) 7.3 Interfacial Tension Gradient and Marangoni Effect..................................................................250 7.4 Surface Dilatational Viscosity...................................................................................................252 7.4.1 Measurement of Surface Dilatational Viscosity............................................................254 7.5 Boussinesq–Scriven Model.......................................................................................................257 7.6 Importance of (cid:3)S and (cid:4)S ............................................................................................................258 7.7 Interfacial Turbulence...............................................................................................................259 7.8 Motions of Drops in a Liquid....................................................................................................261 Summary............................................................................................................................................264 Keywords...........................................................................................................................................264 Notation.............................................................................................................................................264 Exercises ...........................................................................................................................................266 Numerical and Analytical Problems.................................................................................................266 Further Reading................................................................................................................................268 8. MONOLAYERS AND THIN LIQUID FILMS .....................................................270–315 8.1 Introduction ..............................................................................................................................271 8.2 Surfactant Monolayers and their Applications..........................................................................271 8.3 Properties of Monolayers..........................................................................................................272 8.3.1 Measurement of Surface Pressure.................................................................................273 8.3.2 Surface Pressure Isotherm.............................................................................................274 8.3.3 Model of Gas-Phase Monolayer....................................................................................276 8.3.4 Surface Potential...........................................................................................................278 8.3.5 Monolayers at Liquid–Liquid Interfaces.......................................................................279 8.4 Langmuir–Blodgett Films.........................................................................................................279 8.5 Surface Diffusion......................................................................................................................282 8.5.1 The Apparatus...............................................................................................................283 8.5.2 Measurement Procedure................................................................................................284 8.5.3 Determination of D ......................................................................................................285 s 8.6 Thin Liquid Films.....................................................................................................................286 8.6.1 Critical Film Thickness.................................................................................................287 8.6.2 Hydrostatics of Thin Liquid Films................................................................................292 8.6.3 Drainage of Liquid Films..............................................................................................293 8.6.4 The Lubrication Flow....................................................................................................295 8.6.5 Film-Drainage Time......................................................................................................298 8.6.6 Stability of Thin Liquid Films.......................................................................................302 8.6.7 Black Films...................................................................................................................303 Summary............................................................................................................................................306 Keywords...........................................................................................................................................307 Notation.............................................................................................................................................307 Exercises ...........................................................................................................................................309 Numerical and Analytical Problems.................................................................................................310 Appendix............................................................................................................................................311 Further Reading................................................................................................................................312 9. EMULSIONS, MICROEMULSIONS AND FOAMS ...........................................316–371 9.1 Introduction ..............................................................................................................................317 9.2 Emulsions.................................................................................................................................317 9.2.1 Preparation of Emulsions..............................................................................................318 (cid:3)(cid:2)(cid:2)(cid:2) (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) 9.2.2 Stability of Emulsions...................................................................................................319 9.2.3 Ostwald Ripening .........................................................................................................321 9.2.4 Flocculation and Coalescence of Drops........................................................................324 9.2.5 Phase Inversion.............................................................................................................338 9.2.6 Application of Emulsions..............................................................................................339 9.3 Microemulsions........................................................................................................................340 9.3.1 Winsor’s Classification of Microemulsions ..................................................................340 9.3.2 Stability of Microemulsions..........................................................................................345 9.3.3 Rheology of Microemulsions........................................................................................351 9.3.4 Applications of Microemulsions...................................................................................353 9.4 Foams .......................................................................................................................................353 9.4.1 Preparation of Foams and Measurement of their Stability............................................355 9.4.2 Structure of Foams........................................................................................................356 9.4.3 Foam Drainage..............................................................................................................358 9.4.4 Applications of Foams..................................................................................................360 Summary............................................................................................................................................360 Keywords...........................................................................................................................................361 Notation.............................................................................................................................................362 Exercises ...........................................................................................................................................364 Numerical and Analytical Problems.................................................................................................366 Further Reading................................................................................................................................368 10. BIOLOGICAL INTERFACES.............................................................................372–409 10.1 Introduction ..............................................................................................................................372 10.2 Protein Adsorption at Interfaces................................................................................................373 10.2.1 Adsorption of Proteins at Solid–Liquid Interfaces......................................................374 10.2.2 Adsorption of Proteins at Fluid–Fluid Interfaces........................................................377 10.3 Biological Membranes..............................................................................................................381 10.4 Interfacial Forces......................................................................................................................384 10.4.1 van der Waals Force....................................................................................................385 10.4.2 Hydration Force..........................................................................................................385 10.4.3 Steric Forces ...............................................................................................................387 10.4.4 Electrostatic Double Layer Force................................................................................390 10.4.5 Hydrophobic Forces....................................................................................................392 10.5 Cell Adhesion ...........................................................................................................................393 10.6 Pulmonary Surfactant ...............................................................................................................396 10.7 Biomaterials..............................................................................................................................398 Summary............................................................................................................................................400 Keywords...........................................................................................................................................401 Notation.............................................................................................................................................401 Exercises ...........................................................................................................................................403 Numerical and Analytical Problems.................................................................................................404 Appendix............................................................................................................................................405 Further Reading................................................................................................................................406 11. NANOMATERIALS ............................................................................................410–451 11.1 Introduction ..............................................................................................................................411 11.2 Approaches for the Synthesis of Nanomaterials .......................................................................412 (cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:4)(cid:5)(cid:7) (cid:2)(cid:4) 11.3 Self-Assembly and Structure ....................................................................................................412 11.4 Synthesis of Nanoparticles........................................................................................................414 11.4.1 Homogeneous Nucleation...........................................................................................414 11.4.2 Microemulsion-Based Methods..................................................................................421 11.4.3 Synthesis of Carbon Fullerenes...................................................................................422 11.5 Synthesis of Nanowires, Nanorods and Nanotubes...................................................................425 11.5.1 Nanowires and Nanorods............................................................................................425 11.5.2 Nanotubes...................................................................................................................429 11.6 Deposition of Thin Films..........................................................................................................435 11.7 Synthesis of Microporous and Mesoporous Materials..............................................................438 11.8 Lithographic Techniques...........................................................................................................442 11.9 Toxic Effects of Nanomaterials.................................................................................................444 Summary............................................................................................................................................445 Keywords...........................................................................................................................................445 Notation.............................................................................................................................................446 Exercises ...........................................................................................................................................446 Numerical and Analytical Problems.................................................................................................448 Further Reading................................................................................................................................448 12. INTERFACIAL REACTIONS .............................................................................452–493 12.1 Introduction ..............................................................................................................................452 12.2 Reactions at Solid–Fluid Interfaces ..........................................................................................453 12.2.1 Langmuir–Hinshelwood Model ..................................................................................455 12.2.2 External Transport Processes ......................................................................................460 12.2.3 Determination of Mass and Heat Transfer Coefficients ..............................................464 12.2.4 Internal Transport Processes .......................................................................................465 12.3 Interfacial Polycondensation.....................................................................................................469 12.4 Gas–Liquid and Liquid–Liquid Interfacial Reactions...............................................................476 12.5 Reactions at Biointerfaces ........................................................................................................477 12.6 Micellar Catalysis.....................................................................................................................481 12.7 Phase Transfer Catalysis...........................................................................................................484 Summary............................................................................................................................................485 Keywords...........................................................................................................................................486 Notation.............................................................................................................................................486 Exercises ...........................................................................................................................................489 Numerical and Analytical Problems.................................................................................................490 Further Reading................................................................................................................................492 INDEX .......................................................................................................................495–503

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