SURFACTANTS AND INTERFACIAL PHENOMENA SURFACTANTS AND INTERFACIAL PHENOMENA THIRD EDITION Milton J. Rosen Surfactant Research Institute Brooklyn College The City University of New York A JOHN WILEY & SONS, INC., PUBLICATION Copyright # 2004 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
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Surface active agents.1–dc22 2004048079 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 Contents Preface xiii 1 Characteristic Features of Surfactants 1 A Conditions Under Which Interfacial Phenomena and Surfactants Become Significant 2 B General Structural Features and Behavior of Surfactants 2 1 General Use of Charge Types 4 2 General Effects of the Nature of the Hydrophobic Group 5 I Characteristic Features and Uses of Commercially Available Surfactants 6 I.A Anionics 7 1 Carboxylic Acid Salts 7 2 Sulfonic Acid Salts 8 3 Sulfuric Acid Ester Salts 12 4 Phosphoric and Polyphosphoric Acid Esters 15 5 Fluorinated Anionics 15 I.B Cationics 16 1 Long-Chain Amines and Their Salts 17 2 Acylated Diamines and Polyamines and Their Salts 17 3 Quaternary Ammonium Salts 18 4 Polyoxyethylenated (POE) Long-Chain Amines 19 5 Quaternized POE Long-Chain Amines 19 6 Amine Oxides 19 I.C Nonionics 20 1 POE Alkylphenols, Alkylphenol ‘‘Ethoxylates’’ 20 2 POE Straight-Chain Alcohols, Alcohol ‘‘Ethoxylates’’ 21 3 POE Polyoxypropylene glycols 22 4 POE Mercaptans 22 5 Long-Chain Carboxylic Acid Esters 23 6 Alkanolamine ‘‘Condensates,’’ Alkanolamides 24 7 Tertiary Acetylenic Glycols and Their ‘‘Ethoxylates’’ 24 8 POE Silicones 25 9 N-Alkylpyrrolidones 25 v vi CONTENTS 10 Alkylpolyglycosides 26 I.D Zwitterionics 26 1 pH-Sensitive Zwitterionics 26 2 pH-Insensitive Zwitterionics 28 I.E Newer Surfactants Based Upon Renewable Raw Materials 28 1 a-Sulfofatty Acid Methyl Esters (SME) 28 2 Acylated Aminoacids 29 3 N-Acyl L-Glutamates (AG) 29 4 N-Acyl Glycinates 29 5 N-Acyl DL-Alaninates 30 6 Other Acylated Aminoacids 30 7 Nopol Alkoxylates 30 II Environmental Effects of Surfactants 31 II.A Surfactant Biodegradability 31 II.B Surfactant Toxicity To and Bioconcentration in Marine Organisms 31 III Some Useful Generalizations 32 References 33 Problems 33 2 Adsorption of Surface-Active Agents at Interfaces: The Electrical Double Layer 34 I The Electrical Double Layer 35 II Adsorption at the Solid–Liquid Interface 38 II.A Mechanisms of Adsorption and Aggregation 39 II.B Adsorption Isotherms 42 1 The Langmuir Adsorption Isotherm 44 II.C Adsorption from Aqueous Solution Onto Adsorbents with Strongly Charged Sites 47 1 Ionic Surfactants 47 2 Nonionic Surfactants 52 3 pH Change 53 4 Ionic Strength 53 5 Temperature 53 II.D Adsorption from Aqueous Solution Onto Nonpolar, Hydrophobic Adsorbents 54 II.E Adsorption from Aqueous Solution Onto Polar Adsorbents without Strongly Charged Sites 56 II.F Effects of Adsorption from Aqueous Solution on the Surface Properties of the Solid Adsorbent 57 1 Substrates with Strongly Charged Sites 57 2 Nonpolar Adsorbents 58 CONTENTS vii II.G Adsorption from Nonaqueous Solution 58 II.H Determination of the Specific Surface Areas of Solids 59 III Adsorption at the Liquid–Gas (L/G) and Liquid–Liquid (L/L) Interfaces 59 III.A The Gibbs Adsorption Equation 60 III.B Calculation of Surface Concentrations and Area per Molecule at the Interface By Use of the Gibbs Equation 62 III.C Effectiveness of Adsorption at the L/G and L/L Interfaces 64 III.D The Szyszkowski, Langmuir, and Frumkin Equations 82 III.E Efficiency of Adsorption at the L/G and L/L Interfaces 83 III.F Calculation of Thermodynamic Parameters of Adsorption at the L/G and L/L Interfaces 87 III.G Adsorption from Mixtures of Two Surfactants 95 References 97 Problems 103 3 Micelle Formation by Surfactants 105 I The Critical Micelle Concentration (CMC) 105 II Micellar Structure and Shape 107 II.A The Packing Parameter 107 II.B Surfactant Structure and Micellar Shape 109 II.C Liquid Crystals 110 III Micellar Aggregation Numbers 113 IV Factors Affecting the Value of the CMC in Aqueous Media 120 IV.A Structure of the Surfactant 121 1 The Hydrophobic Group 121 2 The Hydrophobic Group 138 3 The Counterion in Ionic Surfactants: Degree of Binding to the Micelle 139 4 Empirical Equations 144 IV.C Organic Additives 146 1 Class I Materials 146 2 Class II Materials 147 IV.D The Presence of a Second Liquid Phase 148 IV.E Temperature 149 V Micellization in Aqueous Solution and Adsorption at the Aqueous Solution–Air or Aqueous Solution–Hydrocarbon Interface 149 V. The CMC/C20 ratio 149 VI CMCs in Nonaqueous Media 157 VII Equations for the CMC Based on Theoretical Considerations 157 VIII Thermodynamic Parameters of Micellization 161 viii CONTENTS IX Mixed Micelle Formation in Mixtures of Two Surfactants 167 References 168 Problems 175 4 Solubilization by Solutions of Surfactants: Micellar Catalysis 178 I Solubilization in Aqueous Media 179 I.A Locus of Solubilization 179 I.B Factors Determining the Extent of Solubilization 181 1 Structure of the Surfactant 182 2 Structure of the Solubilizate 184 3 Effect of Electrolyte 185 4 Effect of Monomeric Organic Additives 185 5 Effect of Polymeric Organic Additives 186 6 Mixed Anionic–Nonionic Micelles 187 7 Effect of Temperature 188 8 Hydrotropy 189 I.C Rate of Solubilization 190 II Solubilization in Nonaqueous Solvents 190 II.A Secondary Solubilization 192 III Some Effects of Solubilization 193 III.A Effect of Solubilization on Micellar Structure 193 III.B Change in the Cloud Points of Aqueous Solutions of Nonionic Surfactants 193 III.C Reduction of the CMC 197 III.D Miscellaneous Effects of Solubilization 198 IV Micellar Catalysis 198 References 202 Problems 206 5 Reduction of Surface and Interfacial Tension by Surfactants 208 I Efficiency in Surface Tension Reduction 212 II Effectiveness in Surface Tension Reduction 214 II.A The Krafft Point 214 II.B Interfacial Parameter and Chemical Structural Effects 215 III Liquid–Liquid Interfacial Tension Reduction 229 III.A Ultralow Interfacial Tension 230 IV Dynamic Surface Tension Reduction 234 IV.A Dynamic Regions 234 IV.B Apparent Diffusion Coefficients of Surfactants 237 References 238 Problems 242 CONTENTS ix 6 Wetting and Its Modification by Surfactants 243 I Wetting Equilibria 243 I.A Spreading Wetting 243 1 The Contact Angle 246 2 Measurement of the Contact Angle 247 I.D Adsorption and Wetting 253 II Modification of Wetting by Surfactants 255 II.A General Considerations 255 II.B Hard Surface (Equilibrium) Wetting 256 II.C Textile (Nonequilibrium) Wetting 258 II.D Effect of Additives 268 III Synergy in Wetting by Mixtures of Surfactants 269 IV Superspreading (Superwetting) 270 References 273 Problems 275 7 Foaming and Antifoaming by Aqueous Solutions of Surfactants 277 I Theories of Film Elasticity 278 II Factors Determining Foam Persistence 282 II.A Drainage of Liquid in the Lamellae 282 II.B Diffusion of Gas Through the Lamellae 283 II.C Surface Viscosity 284 II.D The Existence and Thickness of the Electrical Double Layer 284 III The Relation of Surfactant Chemical Structure to Foaming in Aqueous Solution 285 III.A Efficiency as a Foaming Agent 285 III.B Effectiveness as a Foaming Agent 287 III.C Low-Foaming Surfactants 293 IV Foam-Stabilizing Organic Additives 294 V Antifoaming 297 VI Foaming of Aqueous Dispersions of Finely Divided Solids 298 References 299 Problems 301 8 Emulsification by Surfactants 303 I Macroemulsions 304 I.B Factors Determining Stability 305 x CONTENTS 1 Physical Nature of the Interfacial Film 306 2 Existence of an Electrical or Steric Barrier to Coalescence on the Dispersed Droplets 308 3 Viscosity of the Continuous Phase 309 4 Size Distribution of Droplets 309 5 Phase Volume Ratio 309 6 Temperature 310 I.E Theories of Emulsion Type 314 1 Qualitative Theories 314 2 Kinetic Theory of Macroemulsion Type 316 II Microemulsions 317 III Nanoemulsions 319 IV Selection of Surfactants as Emulsifying Agents 320 IV.A The HLB Method 321 IV.B The PIT Method 324 IV.C The HLD Method 326 V Demulsification 327 References 327 Problems 330 9 Dispersion and Aggregation of Solids in Liquid Media by Surfactants 332 I Interparticle Forces 332 I.A Soft (electrostatic) and van der Waals Forces: DLVO Theory 332 1 Limitations of the DLVO Theory 338 I.B Steric Forces 339 II Role of the Surfactant in the Dispersion Process 341 II.A Wetting of the Powder 342 II.B Deaggregation or Fragmentation of Particle Clusters 342 II.C Prevention of Reaggregation 342 III Coagulation or Flocculation of Dispersed Solids by Surfactants 343 III.A Neutralization or Reduction of the Potential at the Stern Layer of the Dispersed Particles 343 III.C Reversible Flocculation 344 IV The Relation of Surfactant Chemical Structure to Dispersing Properties 345 IV.A Aqueous Dispersions 345 IV.B Nonaqueous Dispersions 349 CONTENTS xi References 350 Problems 351 10 Detergency and Its Modification by Surfactants 353 I Mechanisms of the Cleaning Process 353 I.A Removal of Soil from Substrate 354 1 Removal of Liquid Soil 355 2 Removal of Solid Soil 357 I.B Suspension of the Soil in the Bath and Prevention of Redeposition 359 1 Solid Particulate Soils: Formation of Electrical and Steric Barriers; Soil Release Agents 359 2 Liquid Oily Soil 359 I.D Dry Cleaning 361 II Effect of Water Hardness 362 II.B Lime Soap Dispersing Agents 364 III Fabric Softeners 365 IV The Relation of the Chemical Structure of the Surfactant to Its Detergency 367 IV.A Effect of Soil and Substrate 367 1 Oily Soil 367 2 Particulate Soil 370 3 Mixed Soil 370 IV.B Effect of the Hydrophobic Group of the Surfactant 371 IV.C Effect of the Hydrophilic Group of the Surfactant 372 IV.D Dry Cleaning 374 References 374 Problems 378 11 Molecular Interactions and Synergism in Mixtures of Two Surfactants 379 I Evaluation of Molecular Interaction Parameters 380 I.A Notes on the Use of Equations 11.4 382 II Effect of Chemical Structure and Molecular Environment on Molecular Interaction Parameters 384 III Conditions for the Existence of Synergism 397 III.A Synergism or Antagonism (Negative Synergism) in Surface or Interfacial Tension Reduction Efficiency 398 III.B Synergism or Antagonism (Negative Synergism) in Mixed Micelle Formation in Aqueous Medium 400 xii CONTENTS III.C Synergism or Antagonism (Negative Synergism) in Surface or Interfacial Tension Reduction Effectiveness 401 III.D Selection of Surfactants Pairs for Optimal Interfacial Properties 405 IV The Relation between Synergism in Fundamental Surface Properties and Synergism in Surfactant Applications 405 References 410 Problems 413 12 Gemini Surfactants 415 I Fundamental Properties 415 II Interaction with Other Surfactant 420 III Performance Properties 423 References 424 Problems 426 Answers to Problems 428 Index 433 Preface The more than a decade since publication of the second edition has seen considerable progress in a number of important areas of surfactant chemistry, necessitating the publication of a third edition.