THE SCIENCE OF DEFOAMING Theory, Experiment and Applications Peter R. Garrett @Taylor & CRC Press Francis Group Boca Raton London NewYork CRC Press is an imprint of the Taylor & Francis Group, an informa business
Contents Preface Author xxiii xxv Chapter 1 Some General Properties of Foams 1 1.1 Introduction 1 1.2 Structure of Foams 1 1.3 Foam Films 5 1.3.1 Surface Tension Gradients and Foam Film Stability...5 1.3.2 Drainage Processes in Foam Films 9 1.3.3 Disjoining Forces and Foam Film Stability 14 1.4 Processes Accompanying Aging of Foam 18 1.4.1 Capillary Pressure Gradients 18 1.4.2 Foam Drainage 21 1.4.3 Bubble Coarsening (Diffusional Disproportionation)... 24 1.5 Summarizing Remarks 28 Acknowledgment 29 References 29 Chapter 2 Experimental Methods for Study of Foam and Antifoam Action 33 2.1 Introduction 33 2.2 Measurement of Foam 33 2.2.1 Bartsch Method: Hand Shaking Measuring Cylinders 33 2.2.2 Automated Shake Tests 35 2.2.3 Ross-Miles Method 35 2.2.4 Tumbling Cylinders 36 2.2.5 Gas Bubbling 37 2.2.6 Direct Air Injection 38 2.2.7 Measurement of Bubble Size Distributions 39 2.3 Observations with Single Foam Films 41 2.3.1 Scheludko Cells 41 2.3.1.1 Films Containing Antifoam Drops 41 2.3.1.2 Measurement of Disjoining Pressure Isotherms of Air-Liquid-Air Foam Films 43 2.3.2 Dippenaar Cell 44 2.3.3 Large Vertical Films 45 xiii
xiv Contents 2.4 Air-Water-Oil Pseudoemulsion Films 46 2.4.1 Direct Observation of Pseudoemulsion Films 46 2.4.2 Measurement of Disjoining Pressure Isotherms for Air-Water-Oil Pseudoemulsion Films 48 2.4.3 Direct Measurements of Pseudoemulsion Film Rupture Pressures 49 2.5 Spreading Behavior of Oils 52 2.6 Summarizing Remarks 53 References 54 Chapter 3 Oils at Interfaces: Entry Coefficients, Spreading Coefficients, and Thin Film Forces 57 3.1 Introduction 57 3.2 Classic Entry and Spreading Coefficients 58 3.3 Generalized Entry Coefficients, Pseudoemulsion Films, and Thin Film Forces 61 3.3.1 Definitions 61 3.3.2 Case Where Generalized Entry Coefficient, g > 0...65 3.3.3 Case Where Generalized Entry Coefficient, Eg< 0...68 3.3.4 Magnitude of Generalized Entry Coefficients 70 3.4 Mode of Rupture of Pseudoemulsion Films 72 3.4.1 Disjoining Pressures and Stability of Pseudoemulsion Films 72 3.4.2 Surface Tension Gradients and Stability of Pseudoemulsion Films 78 3.5 Generalized Spreading Coefficients and Thin Film Forces... 79 3.6 Spreading Behavior of Typical Antifoam Oils on Aqueous Surfaces 85 3.6.1 Hydrocarbon Oils 85 3.6.1.1 Spreading and Wetting Behavior of Hydrocarbons on Surface of Pure Water... 85 3.6.1.2 Complete and Pseudo-Partial Wetting Behavior of Hydrocarbons on the Surfaces of Aqueous Surfactant Solutions 87 3.6.1.3 Non-Spreading (Partial Wetting) by Hydrocarbons on the Surfaces of Aqueous Surfactant Solutions 94 3.6.2 Polydimethylsiloxane Oils 96 3.6.2.1 Complete and Pseudo-Partial Wetting Behavior of Polydimethylsiloxanes on the Surfaces of Pure Water and Aqueous Surfactant Solutions 96
Contents xv 3.6.2.2 Rates of Spreading of Polydimefhylsiloxanes on the Surfaces of Pure Water and Aqueous Surfactant Solutions 104 3.6.3 Effect of Spread Hydrocarbon and Polydimethylsiloxane Oils on the Stability of Pseudoemulsion Films 106 3.7 Non-Equilibrium Effects due to Surfactant Transport 108 3.8 Summarizing Remarks 108 References 110 Chapter 4 Mode of Action of Antifoams 115 4.1 Introduction 115 4.2 Antifoam Effects due to Solubilized Oils 116 4.3 Effect on Foamability of Mesophase Precipitation in Aqueous Surfactant Solutions 121 4.4 Surface Tension Gradients and Theories of Antifoam Mechanism 128 4.4.1 General Considerations 128 4.4.2 Surface Tension Gradients Induced by Spreading Antifoam 129 4.4.3 Elimination of Surface Tension Gradients 138 4.5 Oil Bridges and Antifoam Mechanism 141 4.5.1 Oil Bridges in Foam Films 141 4.5.2 Line Tensions and Antifoam Behavior of Oil Lenses... 153 4.5.3 Oil Bridges in Plateau Borders and Stability of Pseudoemulsion Films 157 4.6 Antifoam Behavior of Emulsified Liquids 165 4.6.1 Antifoam Effects of Neat Oils in Aqueous Foaming Systems 165 4.6.1.1 Early Work 165 4.6.1.2 Short-Chain Alcohols 167 4.6.1.3 n-alkanes 175 4.6.1.4 Neat Polydimethylsiloxane Oils 180 4.6.2 Antifoam Effects of Neat Oils in Non-Aqueous Foaming Systems 183 4.6.3 Partial Miscibility and Antifoam Effects 185 4.6.3.1 Origins of Partial Miscibility in Binary Liquid Mixtures 185 4.6.3.2 Systems with Lower Critical Temperatures 188 4.6.3.3 Systems with Higher Critical Temperatures 198
xvi Contents 4.7 Inert Hydrophobic Particles and Capillary Theories of Antifoam Mechanism for Aqueous Systems 201 4.7.1 Early Work 201 4.7.2 Experimental Observations Concerning Contact Angles and Particle Bridging Mechanism 203 4.7.3 Theoretical Considerations Concerning Particle Geometry and Contact Angle Conditions for Antifoam Action by Smooth Particles 216 4.7.3.1 Particles with Curved Surfaces and No Edges 216 4.7.3.2 Particles with Edges 216 4.7.3.3 Models of Foam Film Rupture by Particles Using Surface Energy Minimization 224 4.7.4 Effect of Rugosities on Antifoam Action of Particles 228 4.7.5 Rugosities and Stability of Air-Water-Solid Films 233 4.7.6 Particle Size and Kinetics of Foam Film... Rupture 239 4.7.7 Antifoam Effects of Calcium Soaps 243 4.7.8 Melting of Hydrophobic Particles and Antifoam Behavior 247 4.8 Mixtures of Hydrophobic Particles and Oils as Antifoams for Aqueous Systems 249 4.8.1 Antifoam Synergy 249 4.8.2 Early Patent Literature 251 4.8.3 Role of Oil in Synergistic Oil-Particle Antifoams...252 4.8.4 Early Hypotheses Concerning Role of Particles in Synergistic Oil-Particle Antifoams 263 4.8.5 Role of Particles in Synergistic Oil-Particle Antifoams 267 4.8.5.1 Experimental Observation 267 4.8.5.2 Spherical Particles, Spread Oil Layers, and Rupture of Pseudoemulsion Films 272 4.8.5.3 Smooth Particles with Edges in Absence of Spread Oil Layers 277 4.8.5.4 Smooth Particles with Edges in Presence of Spread Oil Layers 281 4.8.5.5 Rough Particles with Many Edges 281 4.8.6 Antifoam Dimensions and Kinetics 290 4.9 Summarizing Remarks 292 Acknowledgments 295 Appendix 4.1 295 References 302
Contents xvii Chapter 5 Effect of Antifoam Concentration on Volumes of Foam Generated by Air Entrainment 309 5.1 Phenomenology 309 5.1.1 Introduction 309 5.1.2 Dispersion of Single Antifoam 310 5.1.3 Mixed Dispersions of Two Antifoams 313 5.1.4 Relative Effectiveness of Antifoam Entities and Foam Structure 318 5.2 Statistical Theory of Antifoam Action 320 5.2.1 Assumptions 320 5.2.2 Factors Determining Number of Antifoam Entities in Foam Film 324 5.2.3 Calculation of Volume of Air in Foam in Presence of Antifoam 330 5.2.4 Limitations of Theory 334 5.3 Summarizing Remarks 336 Appendix 5.1 Effect of Excluded Volume on Antifoam Concentration in a Film Exhibiting Reynolds Drainage 338 A5.1.1 Mean Flow Velocity of Antifoam Entities 338 A5.1.2 Effect of Excluded Volume on Antifoam Concentration in a Draining Film 339 References 341 Chapter 6 Deactivation of Mixed Oil-Particle Antifoams during Dispersal and Foam Generation in Aqueous Media 343 6.1 Introduction 343 6.2 Deactivation of Antifoam Effect of Polydimethylsiloxane Oils without Particles 344 6.3 Early Work with Hydrophobed Silica Polydimethylsiloxane Antifoams 346 6.3.1 Separation of Silica from Oil 346 6.3.2 Equilibration and Deactivation 347 6.3.3 Deactivation, Emulsification, and Drop Sizes 348 6.4 Deactivation of Hydrophobed Silica Polydimethylsiloxane Antifoam by Disproportionation 351 6.4.1 Experimental Evidence 351 6.4.2 Theoretical Considerations Concerning Deactivation by Disproportionation 357 6.5 Effect of Oil Viscosity on Deactivation of Hydrophobed Silica-Polydimethylsiloxane Antifoams 363 6.6 Deactivation in Other Types of Oil-Particle Antifoams 366 6.7 Theories of Foam Volume Growth in Presence of Deactivating Antifoam 368
xviii Contents 6.7.1 Antifoam-Bubble Heterocoalescence-Kinetic Model of Pelton and Goddard for Foam Generation by Sparging 368 6.7.2 Modified Antifoam-Bubble Heterocoalescence- Kinetic Model Using a Statistical Distribution of Antifoam Drops over Bubbles 373 6.7.3 Combination of Kinetic Model of Antifoam Deactivation with Kinetic Model of Antifoam Action 376 6.7.4 Combination of Kinetic Model of Antifoam Deactivation by Disproportionation with Empirical Expression for Antifoam Action 379 6.8 Summarizing Remarks 383 Acknowledgment 386 References 386 Chapter 7 Mechanical Methods for Defoaming 389 7.1 Introduction 389 Devices 389 7.2 Defoaming Using Rotary 7.2.1 Designs of Rotary Devices Described in Scientific Literature 389 7.2.2 Commercial Rotary Defoamers 398 7.2.3 Defoaming Mechanisms of Rotary Devices 400 7.2.3.1 Role of Centrifugal Force 400 7.2.3.2 Role of Shear and Impact Forces on Bubbles in Mechanical Defoaming 404 7.2.3.3 Defoaming by Inherent Liquid Spray 407 7.3 Defoaming Using Ultrasound 409 7.3.1 Brief History of Defoaming by Ultrasound 409 7.3.2 Defoaming Mechanism of Ultrasound 415 7.4 Defoaming Using Packed Beds of Appropriate Wettability... 421 7.5 Summarizing Remarks 422 Appendix 7.1 423 References 428 Chapter 8 Antifoams for Detergent Products 431 8.1 Introduction 431 8.2 Powders for Machine Washing of Laundry 433 8.2.1 Front-Loading Drum-Type Textile Washing Machines 433 8.2.2 Use of Fatty Acids and Soaps 435 8.2.3 Use of Non-Soap Particulate Antifoams 439 8.2.4 Use of Hydrocarbon-Hydrophobic Particle Mixtures 441
Contents xix 8.2.4.1 Hydrocarbon Mixtures with Alkyl Phosphoric Acid Derivatives 441 8.2.4.2 Hydrocarbon Mixtures with Non- Phosphorous-Containing Organic Compounds 446 8.2.5 Use of Polydimethylsiloxane-Based Antifoams 450 8.2.5.1 General Properties 450 8.2.5.2 Storage Deactivation and Incorporation in Detergent Powders 453 8.2.5.3 Dispensing 456 8.2.5.4 Enhancement of Antifoam Effectiveness 457 8.2.6 Hydrocarbon-Based Simulation of Dimethylsiloxane-Based Antifoams 460 8.3 Liquids for Machine Washing of Laundry 461 8.3.1 General Properties 461 8.3.2 Incorporation of Polyorganosiloxane-Hydrophobic Silica Antifoams in Detergent Liquids 462 8.4 Machine Dishwashing 467 8.5 General Hard-Surface Cleaning Products 469 8.6 Summarizing Remarks 471 Appendix 8.1 471 References 476 Chapter 9 Control of Foam in Waterborne Latex Paints and Varnishes 481 9.1 Introduction 481 9.2 Foam and Antifoam Behavior 485 9.2.1 General Considerations 485 9.2.2 Effect of Stratified Layers of Polymer Latex Particles on Foam and Pseudoemulsion Film Stability 488 9.3 Specific Issues Concerning Oil-Based Antifoams 489 9.3.1 Incorporation in Paints and Varnishes 489 9.3.2 Defect Formation in Drying Paint Films 492 9.3.2.1 General Considerations 492 9.3.2.2 Experimental and Theoretical Studies of Cratering Caused by Marangoni Effect Induced by Spreading Oil Drops 495 9.3.2.3 Putative Craters Caused by Non- Spreading Oil Drops Bridging Paint Films 497 9.4 Summarizing Remarks 499 References 500
XX Contents Chapter 10 Antifoams for Gas-Oil Separation in Crude Oil Production 503 10.1 Introduction 503 10.2 Surface Activity at Gas-Hydrocarbon and Gas-Crude Oil Interfaces 504 10.3 Causes of Foam Formation in Gas-Crude Oil Systems 509 10.3.1 Disjoining Pressures 509 10.3.2 Origin of Surface Tension Gradients at Gas-Crude Oil Interfaces 510 10.3.3 Experimental Observations of Foam Behavior 511 10.4 Use of Antifoams 515 10.4.1 General Considerations 515 10.4.2 Polydimethylsiloxanes and Substituted Polydimethylsiloxanes 517 10.4.2.1 Effect of Solubility of Antifoam Oils 517 10.4.2.2 Mode of Antifoam Action in Crude Oils 520 10.4.3 Other Materials 524 10.5 Summarizing Remarks 525 References 526 Chapter 11 Medical Applications of Defoaming 529 11.1 Introduction 529 11.2 Use of Simethicone Antifoam in Treatment of Gastrointestinal Gas 530 11.2.1 Therapeutic Application 530 11.2.2 Use of Simethicone in Endoscopy 532 11.3 Defoaming of Blood during Cardiopulmonary Bypass Surgery 533 11.3.1 Gas Bubble Oxygenators and Use of Antifoams 533 11.3.2 Mechanism of Polydimethylsiloxane- Hydrophobed Silica-Coated Porous Defoamers 535 11.3.3 Polydimethylsiloxane-Hydrophobed Silica Antifoam as Source of Emboli 537 11.3.4 Cardiotomy Defoam ing 539 11.3.5 Defoaming in Cardiopulmonary Bypass Blood Circuits, Which Include Membrane Oxygenators and Cardiotomy/Venous Reservoirs 540 11.3.6 Defoaming Systems Avoiding Use of Polydimethylsiloxane-Based Antifoam 542 11.3.6.1 Potential Replacements for PDMS- Hydrophobed Silica in Cardiotomy Reservoirs 542
Contents xxi 11.3.6.2 Potential Use of Defoamer Elements with High Air-Blood Contact Angles 544 11.3.6.3 Removal of Gaseous Microemboli 545 11.4 Summarizing Remarks 549 References 551 Frequently Used Symbols and Abbreviations 555 Index 559