M j rosen surfactants and interfacial phenomena

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 Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-646-8600, or on the web at www.copyright.com Requests to the Publisher for permission should be addressed to the 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U.S at 877-762-2974, outside the U.S at 317-572-3993 or fax 317-572-4002 Wiley also publishes its books in a variety of electronic formats Some content that appears in print, however, may not be available in electronic format Library of Congress Cataloging-in-Publication Data is available Rosen, Milton J Surfactants and interfacial phenomena / Milton J Rosen – 3rd ed p cm Includes bibliographical references and index ISBN 0-471-47818-0 Surface active agents Surface chemistry I Title TP994.R67 2004 6680 1–dc22 2004048079 Printed in the United States of America 10 Contents Preface xiii Characteristic Features of Surfactants A Conditions Under Which Interfacial Phenomena and Surfactants Become Significant B General Structural Features and Behavior of Surfactants General Use of Charge Types General Effects of the Nature of the Hydrophobic Group I Characteristic Features and Uses of Commercially Available Surfactants I.A Anionics Carboxylic Acid Salts Sulfonic Acid Salts Sulfuric Acid Ester Salts 12 Phosphoric and Polyphosphoric Acid Esters 15 Fluorinated Anionics 15 I.B Cationics 16 Long-Chain Amines and Their Salts 17 Acylated Diamines and Polyamines and Their Salts 17 Quaternary Ammonium Salts 18 Polyoxyethylenated (POE) Long-Chain Amines 19 Quaternized POE Long-Chain Amines 19 Amine Oxides 19 I.C Nonionics 20 POE Alkylphenols, Alkylphenol ‘‘Ethoxylates’’ 20 POE Straight-Chain Alcohols, Alcohol ‘‘Ethoxylates’’ 21 POE Polyoxypropylene glycols 22 POE Mercaptans 22 Long-Chain Carboxylic Acid Esters 23 Alkanolamine ‘‘Condensates,’’ Alkanolamides 24 Tertiary Acetylenic Glycols and Their ‘‘Ethoxylates’’ 24 POE Silicones 25 N-Alkylpyrrolidones 25 v vi CONTENTS 10 Alkylpolyglycosides 26 I.D Zwitterionics 26 pH-Sensitive Zwitterionics 26 pH-Insensitive Zwitterionics 28 I.E Newer Surfactants Based Upon Renewable Raw Materials 28 a-Sulfofatty Acid Methyl Esters (SME) 28 Acylated Aminoacids 29 N-Acyl L-Glutamates (AG) 29 N-Acyl Glycinates 29 N-Acyl DL-Alaninates 30 Other Acylated Aminoacids 30 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 Adsorption of Surface-Active Agents at Interfaces: The Electrical Double Layer 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 The Langmuir Adsorption Isotherm 44 II.C Adsorption from Aqueous Solution Onto Adsorbents with Strongly Charged Sites 47 Ionic Surfactants 47 Nonionic Surfactants 52 pH Change 53 Ionic Strength 53 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 Substrates with Strongly Charged Sites 57 Nonpolar Adsorbents 58 34 vii CONTENTS 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 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 The Hydrophobic Group 121 The Hydrophobic Group 138 The Counterion in Ionic Surfactants: Degree of Binding to the Micelle 139 Empirical Equations 144 IV.B Electrolyte 144 IV.C Organic Additives 146 Class I Materials 146 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.A 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 References 168 Problems 175 167 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 Structure of the Surfactant 182 Structure of the Solubilizate 184 Effect of Electrolyte 185 Effect of Monomeric Organic Additives 185 Effect of Polymeric Organic Additives 186 Mixed Anionic–Nonionic Micelles 187 Effect of Temperature 188 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 Reduction of Surface and Interfacial Tension by Surfactants 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 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 242 208 215 CONTENTS Wetting and Its Modification by Surfactants ix 243 I Wetting Equilibria 243 I.A Spreading Wetting 243 The Contact Angle 246 Measurement of the Contact Angle 247 I.B Adhesional Wetting 249 I.C Immersional Wetting 251 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 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 Emulsification by Surfactants I Macroemulsions 304 I.A Formation 305 I.B Factors Determining Stability 303 305 x CONTENTS II III IV V Physical Nature of the Interfacial Film 306 Existence of an Electrical or Steric Barrier to Coalescence on the Dispersed Droplets 308 Viscosity of the Continuous Phase 309 Size Distribution of Droplets 309 Phase Volume Ratio 309 Temperature 310 I.C Inversion 311 I.D Multiple Emulsions 313 I.E Theories of Emulsion Type 314 Qualitative Theories 314 Kinetic Theory of Macroemulsion Type 316 Microemulsions 317 Nanoemulsions 319 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 Demulsification 327 References 327 Problems 330 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 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.B Bridging 344 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 Removal of Liquid Soil 355 Removal of Solid Soil 357 I.B Suspension of the Soil in the Bath and Prevention of Redeposition 359 Solid Particulate Soils: Formation of Electrical and Steric Barriers; Soil Release Agents 359 Liquid Oily Soil 359 I.C Skin Irritation 361 I.D Dry Cleaning 361 II Effect of Water Hardness 362 II.A Builders 363 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 Oily Soil 367 Particulate Soil 370 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 I Evaluation of Molecular Interaction Parameters 380 I.A Notes on the Use of Equations 11.1–11.4 382 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 400 379 SELECTION OF SURFACTANTS AS EMULSIFYING AGENTS 323 The HLB value for some types of nonionic surface-active agents can be calculated from their structural groupings (Griffin, 1954) Thus, for fatty acid esters of many polyhydric alcohols,   S HLB ẳ 20  A 8:12ị where S is the saponification number of the ester and A is the acid number of the fatty acid used in the ester For example, glyceryl monostearate has S ¼ 161, A ¼ 198, and hence HLB ¼ 3:8 For esters for which good saponification data are not readily obtainable, the following formula can be used: HLB ẳ EỵP 8:13ị where E is the weight percentage of oxyethylene content and P is the weight percentage of polyol content For materials where a POE chain is the only hydrophilic group, this reduces to HLB ẳ E 8:14ị Thus, a POE cetyl alcohol made from 20 mol of ethylene oxide (77% oxyethylene) would have a calculated HLB of 15.4 A commonly used general formula for nonionics is 20  MH MH þ ML ð8:15Þ Where MH is the formula weight of the hydrophilic portion of the molecule and ML is the formula weight of the lipophilic (hydrophobic) portion of the molecule The water solubility of the surfactant can be used to obtain a rough approximation of its HLB value (Becher, 2001) Behavior in Water No dispersibility Poor dispersion Milky dispersion after vigorous agitation Stable milky dispersion (upper end almost translucent) From translucent to clear Clear solution HLB Range 1– 3– 6 810 1013 13ỵ 324 EMULSIFICATION BY SURFACTANTS There have been numerous attempts to determine HLB numbers from other fundamental properties of surfactants, e.g., from cloud points of nonionics (Schott, 1969), from CMCs (Lin, 1973), from gas chromatography retention times (Becher, 1964; Petrowski, 1973), from NMR spectra of nonionics (Ben-et, 1972), from partial molal volumes (Marszall, 1973), and from solubility parameters (Hayashi, 1967; McDonald, 1970; Beerbower, 1971) Although relations have been developed between many of these quantities and HLB values calculated from structural groups in the molecule, particularly in the case of nonionic surfactants, there are few or no data showing that the HLB values calculated in these fashions are indicative of actual emulsion behavior It has become apparent that although the HLB method is useful as a rough guide to emulsifier selection, it has serious limitations Although, as mentioned previously, the HLB number of a surfactant is indicative of neither its efficiency (the required concentration of the emulsifying agent) nor its effectiveness (the stability of the emulsion), but only of the type of emulsion that can be expected from it, data have accumulated that show that even this is not reliably related to the HLB number It has been pointed out (Shinoda, 1968; Boyd, 1972; Kloet, 2002) that a single surfactant can produce either an O/W or a W/O emulsion, depending on the temperature at which the emulsion is prepared, the shear rate, or, at high oil concentrations, on the ratio of surfactant to oil O/W emulsions can be prepared with certain surfactants over the entire range of HLB numbers from to 17 IV.B The PIT Method A major disadvantage of the HLB method of selecting surfactants as emulsifying agents for a particular system is that it makes no allowance for the change in HLB value with change in the conditions for emulsification (temperature, nature of the oil and water phases, presence of cosurfactants or other additives) For example, we saw in Chapter 5, Section IIIA, that when the temperature is raised, the degree of hydration of a POE nonionic surfactant decreases and the surfactant becomes less hydrophilic Consequently, its HLB must decrease An O/W emulsion made with a POE nonionic surfactant may invert to a W/O emulsion when the temperature is raised; a W/O emulsion may invert to an O/W emulsion when the temperature is lowered The temperature in the middle of the three-phase region at which inversion occurs is known as the phase inversion temperature (PIT) and is the temperature, as we have seen in Chapter 5, Section IIIA, at which the hydrophilic and lipophilic tendencies of the surfactant (or surfactant–cosurfactant mixture) ‘‘balance’’ in that particular system of oil and water phases There is also a very good linear relationship between the PIT and the cloud points (Chapter 4, Section IIIB) of various types of POE nonionic surfactants when the system is saturated with the oil phase (Shinoda and Arai, 1964) Since the oil–water interfacial tension is at a minimum at the PIT, emulsions made at this temperature should have the finest particle size The minimum work needed to create the emulsions is the product of the interfacial tension and the SELECTION OF SURFACTANTS AS EMULSIFYING AGENTS 325 increase in interfacial area (Wmin ¼ gI 
A) and, for a given amount of mechanical work expended,
A should be a maximum at the temperature Since the particle size diminishes as
A increases for a given amount of mechanical work expended, the particle size should be at a minimum at the PIT This is the basis for a method of selecting surfactants as emulsifying agents for a particular system, the PIT method (Shinoda, 1964, 1965, 1968) This method is applicable only to emulsions that show inversion at a particular temperature According to this method, an emulsion made with equal weights of oil and aqueous phases and 3–5% of surfactant is heated and shaken at different temperatures and the temperature at which the emulsion inverts from O/W to W/O, or vice versa, is determined A suitable emulsifier for an O/W emulsion should yield a PIT 20–60 C higher than the storage temperature of the emulsion; for a W/O emulsion, a PIT 10–40 C lower than the storage temperature is recommended (although PITs cannot be determined below 0 C) For optimum stability, Shinoda and Saito (1969) suggest ‘‘emulsification by the PIT method,’’ in which the emulsion is prepared at a temperature 2– 4 C below the PIT and then cooled down to the storage temperature (for O/W emulsions) This is because an emulsion prepared near the PIT has a very fine average particle size but is not very stable to coalescence Cooling it down to a temperature considerably below the PIT increases it stability without significantly increasing its average particle size The PIT is affected by the HLB and the concentration of the surfactant, the polarity of the oil phase, the phase ratio of the bulk phases and the presence of additives in them, and the distribution of POE chain lengths in POE nonionics (Shinoda, 1968; Mitsui, 1970) The PIT appears to be an almost linear function of the HLB value of the surfactant for a given set of emulsification conditions; the higher the HLB value, the greater the PIT This is to be expected, since the larger the ratio of the hydrophilic to the lipophilic moiety in the surfactant molecule, the higher the temperature required to dehydrate it to the point where its structure is balanced When the distribution of POE chain lengths in an emulsion stabilized by a POE nonionic surfactant is broad, its PIT is higher and its stability greater than when the distribution is narrow (Shinoda, 1971) For a POE surfactant with a given HLB value, as the polarity of the oil phase decreases, the PIT increases (The surfactant must be made more lipophilic to match the decreased polarity of the oil.) Thus, to keep the PIT constant (and hence a constant emulsifying power balance), the surfactant used must have a lower HLB value as the polarity of the oil phase decreases The PIT of an emulsion made from binary mixture of oils is the weighted average, by volume, of the PITs of the emulsion made from the individual oils, using the same emulsifying agent (Arai, 1967): PITmixị ẳ PITA fA ỵ PITB fB ð8:16Þ where fA and fB are the volume fractions of oils A and B used in the emulsion 326 EMULSIFICATION BY SURFACTANTS The PIT appears to reach a constant value at 3–5% surfactant concentration when a POE nonionic containing a single POE chain length is used When there is a distribution of POE chain lengths in the surfactant, the PIT decreases very sharply with increase in the concentration of the surfactant when the degree of oxyethylenation is low and less sharply when the degree of oxyethylenation is high As the oil–water ratio increases in an emulsion with a fixed surfactant concentration, the PIT increases However, fixed ratios of surfactant to oil give the same PIT, even when the oil–water ratio varies The higher the surfactant– oil ratio, the lower the PIT Additives, such a paraffin, that decrease the polarity of the oil phase increase the PIT, whereas those, such as oleic acid or lauryl alcohol, that increase its polarity lower the PIT The addition of salts to the aqueous phase decreases the PIT of emulsions made with POE nonionics (Shinoda, 1970) Since the PIT of a hydrocarbon–water emulsion stabilized with a POE nonionic surfactant is, as might be expected, related to the cloud point of an aqueous solution of the nonionic saturated with that hydrocarbon (Chapter 4), these effects on the PIT of emulsions stabilized by POE nonionics are readily understood As mentioned in the discussion (Chapter 4, Section IIIB) of the effect of solubilizate on the cloud points of POE nonionics, long-chain aliphatic hydrocarbons that are solubilized in the inner core of the micelle increase the cloud point, whereas short-chain aromatic hydrocarbons and polar materials that are solubilized between the POE chains decrease it They have the same effect on the PIT: long-chain aliphatic hydrocarbons increase the PIT and therefore tend to form stable O/W emulsions, whereas short-chain aromatics and polar additives decrease it and tend to form stable W/O emulsions (Shinoda, 1964) An increase in the length of the POE chain increases the cloud point and the PIT and consequently increases the tendency to form O/W emulsions, consistent with the generalization that the more water-soluble the emulsifier, the greater its tendency to form O/W emulsions IV.C The HLD Method The method developed originally for microemulsion formulation (Section II above) has been adapted (Salager, 1983, 2000) to macroemulsion formation In this method, the value of the left-hand side of equation 8.10 or 8.11 is called the hydrophiliclipophilic deviation (HLD) When the value equals zero, as in Section II, a microemulsion is formed; when the value is positive, a W/O macroemulsion is preferentially formed; when it is negative, an O/W macroemulsion is preferentially formed The HLD is similar in nature to the Winsor R ratio (equation 5.2) in that when the HLD is larger than, smaller than, or equal to 0, R is larger than, smaller than, or equal to The value of the HLD method is that, on a qualitative basis, it takes into consideration the other components of the system (salinity, cosurfactant, alkane chain length, temperature, and hydrophilic and hydrophobic groups of the surfactant) On the other hand, on a quantitative basis, it requires the experimental evaluation of a number of empirical constants REFERENCES 327 V DEMULSIFICATION In some processes, the emulsification of two liquid phases is an undersirable phenonmenon This often occurs when two immiscible phases are mixed together with considerable agitation, as in industrial extraction processes However, probably the most important case of undersirable emulsification is in the recovery of petroleum from oil reservoirs Crude oil always is associated with water or brine in the reservoir and also contains natural emulsifying agents, such as asphaltenes and resins These, particularly the asphaltenes, together with other components in the petroleum, such as the resins and waxes, form a thick, viscous interfacial film around water droplets, with their polar groups oriented toward the water and their nonpolar groups toward the oil This interfacial film is highly viscous, producing very stable, viscous W/O emulsions To break these emulsions and separate the petroleum from the water in them, various techniques are used, notably the addition of surfactants called demulsifiers or demulsifying agents Demulsification and demulsifiers in petroleum recovery have been discussed by Angle (2001) and Sjoblom (2001), respectively, but there have been few systematic studies (Shetty, 1992; Bhardwaj, 1993) Mechanisms involved in the demulsification by surfactants of petroleum W/O emulsions include adsorption of the surfactant at the oil–water interface and reduction of the interfacial tension, change in the nature of the interfacial film from a highly hydrophobic one to a less hydrophobic one (and, consequently, one more wettable by water), reduction of the viscosity of the interfacial film by penetration into it of the surfactant, and displacement of the original W/O emulsion stabilizers, particularly the asphaltenes, from the interface into the oil phase Since the chemical composition of the crude oil and the natural emulsifying agents contained in it vary greatly, depending upon the material from which it was formed and the conditions of its formation, no one surfactant demulsifier can be used Instead, a ‘‘chemical cocktail’’ is used, containing different surfactants to perform the required functions These include wetting agents, such as di(2-ethylhexyl) sulfoscuccinate, and various polymeric surfactants, such as POE polyoxypropylenes and POE alkylphenol-formaldehyde polymers The structure of the POE (and polyoxypropylenated) material can be ‘‘tailored’’ to meet the different composition of the petroleum REFERENCES Acosta, E., H Uchiyama, D A Sabatini, and J H Harwell, J Surfactants Detgts 5, 151 (2002) Albers, W and J Th G Overbeek, J Colloid Sci 14, 501, 510 (1959) Al-Rikabi, H and J S Osoba, Paper presented at American Chemical Society meeting April 9, 1973, Dallas, TX Angle, C W., in Encyclopedia of Emulsion Technology, J Sjoblom (Ed.), Marcel Dekker, New York, 2001, Chap 24 328 EMULSIFICATION BY SURFACTANTS Anton, R E., N Garces, and A Yajure, J Disp Sci Technol 18, 539 (1997) Arai, H and K Shinoda, J Colloid Interface Sci 25 396 (1967) Atwood, D., L Currie, and P Elworthy, J Colloid Interface Sci 46, 249, 255 (1974) Aveyard, R and J H Clint, in Adsorption and Aggregation of Surfactants in Solution, K L Mittal and D O Shah (Eds.), Marcel Dekker, New York, 2003, p 76 Bancroft, W D., J Phys Chem 17 514 (1913) Barette, D., Memoir de Licence, FUNDP, Namur, Belgium, 1992 Becher, P., in Pesticide formulations, W Van Valkenburg (Ed.), New York, Marcel Dekker, 1973, p 85; 1973b, p 84 Becher, P., J Disp Sci Tech 5, 81 (1984) Becher, P., Emulsions Theory and Practice, 3rd ed., American Chemical Society, Washington, DC, 2001 Becher, P and R L Birkmeier, J Am Chem Soc 41 169 (1964) Beerbower, A and M Hill, McCutcheon’s Detergents and Emulsifiers Annual, Allured Publ Co., Ridgewood, NJ, 1971, pp 223–232 Beerbower, A and M W Hill, Am Cosmet Perfum 87, 85 (1972) Beerbower, A and J Nixon, Div Petr Chem Preprints, American Chemical Society, 14, No 1, 62 (March, 1969) Ben-et G and D Tatarsky, J Am Oil Chem Soc 49, 499 (1972) Bhardwaj, A and S Hartland, J Disp Sci Technol 14 541 (1993) Bourrel, M., J L Salager, R S Schechter, and W H Wade, J Colloid Interface Sci 75, 451 (1980) Boyd, J., C Parkinson, and P Sherman, J Colloid Interface Sci 41, 359 (1972) Brouwer, W M., M S El-Asser, and J W Vanderhoff, Colloids Surf 21, 69 (1986) Chun, H., J Colloid Interface Sci 71, 408 (1979) Cockbain, E G and T S McRoberts, J Colloid Sci 8, 440 (1953) Cooke, C E and J H Schulman, Surface Chemistry, Munksgaard, Copenhagen, Academic, New York, 1965, p 231 Davies, J T and E K Rideal, Interfacial Phenomena, 2nd ed., Academic, New York, 1963, Chap Davis, J T., 2nd Int Congr Surface Activity, London, 1957, 1, p 426 Dungan, S R., in C Solans and H Kunieda (Eds.), Industrial Applications of Microemulsions, Marcel Dekker, New York, 1997, p 147 El-Asser, M S., C D Lack, Y T Choi, T I Min, J W Vanderhoff, and F M Fowkes, Colloids Surf 12, 79 (1984) El-Asser, M S., S C Misra, J W Vanderhoff, and J A Manson, J Coatings Tech 49, 71 (1977) Ford, R E and C G L Furmidge, J Colloid Interface Sci 22 331 (1966) Forster, T., in M Rieger, and L D Rhein (Eds.), Surfactants in Cosmetics, Marcel Dekker, New York, 1997, p 105 Freshwater, D C., B Scarlett, and M J Groves, Am Cosmet Perfum 81, 43 (1966) Friberg, S., J Colloid Interface Sci 29, 155 (1969) Friberg, S., J Am Oil Chem Sco 48, 578 (1971) REFERENCES 329 Friberg, S., J Colloid Interface Sci 55 614 (1976) Garti, N., M Frenkel, and R Shwartz, J Disp Sci Tech 4, 237 (1983) Griffin, W C., J Soc Cosmet Chem 1, 311 (1949) Griffin, W C., J Soc Cosmet Chem 5, 249 (1954) Grimm, W L., T I Min, M S El-Asser, and J W Vanderhoff, J Colloid Interface Sci 94, 531 (1983) Groves, M J., B H Kaye, and B Scarlett, Br Chem Eng 9, 742 (1964) Hansen, C M., J Paint Tech 39 (505), 105; (511), 500 (1967) Hayashi, S., Yukagaku 16, 554 (1967) Hildebrand, J H and R L Scott, The Solubility of Nonelectrolytes, 3rd ed., Dover, New York, 1964 Holmberg, K and E Osterberg, J Disp Sci Tech 7, 299 (1986) Kitchener, J A and P R Mussellwhite, in Emulsion Science, P Sherman (Ed.), Academic, New York, 1968, pp 96ff Kloet, J V and L L Schramm, J Surfactants Detgts 5, 19 (2002) Lin, I J., J P Friend, and Y Zimmels, J Colloid Interface Sci 45, 378 (1973) Magdassi, S., M Frenke, and N Garti, J Disp Sci Tech 5, 49 (1984) Marszall, L., J Pharm Pharmacol 25, 254 (1973) Mathis, G., P Leempoel, J C Ravey, C Selve, and J J Delpuech, J Am Chem Soc 106, 6162 (1984) Matsumoto, S., J Colloid Interface Sci 94, 362 (1983) Matsumoto, S., Y Kita, and D Yonezawa, J Colloid Interface Sci 57, 353 (1976) Matsumoto, S., Y Koh, and A Michiura, J Disp Sci Tech 6, 507 (1985) McDonald, C., Can J Pharm Sci 5, 81 (1970) Mele, S., A Khan, and M Monduzzi, J Surfactants Detgts 5, 381 (2002) Mitsui, T., Y Machida, and F Harusawa, Bull Chem Soc Japan 43, 3044 (1970) Nakajima, H., H Tomomasa, and M Okabe, Proc First World Emulsion Conf., Paris, 1993, V 1, p Omotosho, J A., T K Law, T L Whateley, and A T Florence, Colloid Surf 20, 133 (1986) Osipow, L I., Surface Chemistry, Reinhold, New York, 1962, Chap 11 Petrowski, G E and J R Vanatta, J Am Oil Chem Soc 50, 284 (1973) Prince, L M., J Colloid Interface Sci 29, 216 (1969) Prince, L M., paper presented before 48th Natl Colloid Symp., Austin, Texas, June, 1974 Prince, L M., J Colloid Interface Sci 52, 182 (1975) Prince, L M., presented before 7th N E regional meeting, American Chemical Society, Albany, New York, August 9, 1976 Robbins, M L., paper SPE 5839, presented before Soc Petrol Eng., AIME, Tulsa, OK, March, 1976 Rosano, H L and W E Gerbacia, Proc 6th Int Conf Surface-Active Substances, Zurich, 1972 Sagitani, H., J Am Oil Chem Soc 58, 738 (1981) Saito, Y., T Sato, and Anazawa, J Am Oil Chem Soc 67, 145 (1990) 330 EMULSIFICATION BY SURFACTANTS Salager, J L., A Graciaa, and J Lachaise, J Surfactants Detgts 1, 403 (1998) Salager, J L., N Marquez, A Graciaa, and J Lachaise, Langmuir 16, 5534 (2000) Salager, J L., M Minana-Perez, M Perez-Sanchez, M Ranfrey-Gouveia, and C I Rojas, J Disp Sci Technol 4, 313 (1983) Salager, J L., L Morgan, R S Schechter, W H Wade, and E Vasquez, Soc Petrol Eng J 19 107 (1979) Schomacker, R., Nachr Chem Tech lab 40, 1344 (1992) Schott, H., J Pharm Sci 58, 1443 (1969) Schulman, J H and E G Cockbain, Trans Faraday Sco 36, 661 (1940) Schulman, J and J Leja, Trans Faraday Soc 50, 598 (1954) Shah, D O., 48th Natl Colloid Symposium, Austin, TX, June 1974, preprints, p 173 Sherman, P (Ed.) Emulsion Science, Academic, New York, 1968 Shetty, C A., A D Nikolov, and D T Wasan, J Disp Sci Technol 13, 121 (1992) Shinoda, K., Proc 5th Int Congr Detergency, September, 1968, Balcelona, II, p 275 Shinoda, K and H Arai, J Phys Chem 68, 3485 (1964) Shinoda, K and H Arai, J Colloid Sci 20, 93 (1965) Shinoda, K and S Friberg, Adv Colloid Interface Sci 4, 281 (1975) Schinoda, K and H Saito, J Colloid Interface Sci 30, 258 (1969) Shinoda, K., H Saito, and H Arai, J Colloid Interface Sci 35, 624 (1971) Shinoda, K and H Takeda, J Colloid Interface Sci 32, 642 (1970) Sjoblom, J., Emulsions and Emulsion Stability, Marcel Dekker, New York, 1996 Sjoblom, J., E E Johnsen, A Westvik, M.-H Ese J Djuve, I H Auflem, and H Kallevik, in Encyclopedia of Emulsion Technology, J Sjoblom (Ed.), Marcel Dekker, New York, 2001, Chap 25 Solans, C and H Kunieda, Industrial Applications of Microemulsions, Marcel Dekker, New York, 1996 Tronnier, H and H Bussins, Seifen-Ole-Fette-Wachse 86, 747 (1960) Uchiyama, H., E Acosta, D A Sabatini, and J H Harwell, Ind Eng Chem 39, 2704 (2000) Ugelstad, J., M S El-Asser, and J W Vanderhoff, J Polym Sci Polym Lett 11, 503 (1973) Verzaro, F., M Bourrel, and C Chambu, in Surfactants in Solution, K L Mittal and P Bothorel (Eds.), Vol 6, Plenum New York, 1984, pp 1137–1157 von Smoluchowski, M., Phys Z 17, 557, 585 (1916); Z Phys Chem 92, 129 (1917) Winsor, P., Solvent Properties of Amphiphilic Compounds, Butterworths, London, 1954 PROBLEMS List four different ways of distinguishing O/W from W/O macroemulsions Describe, or give the characteristic properties, of each of the following: (a) macroemulsion (b) nanoemulsion (c) microemulsion (d) multiple emulsion PROBLEMS 331 Discuss the changes in interfacial tension that occur in the conversion of an O/W macroemulsion stabilized by a POE nonionic surfactant to a W/O macroemulsion upon raising the temperature above the cloud point Explain the relationship between gOE, gWE, spreading coefficient, and emulsion type An oil has an HLB of 10 for O/W emulsification Calculate the percentages of C12 H25 ðOC2 H4 Þ2 OH and C12 H25 ðOC2 H4 Þ8 OH that should be used in attempting to emulsify this oil with a mixture of these two surfactants (a) Suggest and explain conditions under which the HLB value for a particular surfactant will vary (a) for a POE nonionic surfactant (b) for an ionic surfactant Describe the effect of the following changes on the tendency of a system of a POE nonionic surfactant, an alkane, and water, to form an O/W emulsion: Increase in the temperature from 25 C to 40 C Change in the alkane from n-octane to n-dodecane Increase in the number of carbon atoms of the hydrophobic group of the surfactant (b) Describe the effect in each case if the surfactant is an anionic surfactant Dispersion and Aggregation of Solids in Liquid Media by Surfactants In many products and processes it is important to obtain significantly stable, uniform dispersions of finely divided solids Paints, pharmaceutical preparations, drilling muds for oil wells, pigments, and dyestuffs are commonly used as suspensions of finely divided solids in some liquid medium However, when a preformed, finely divided solid is immersed in a liquid, it often does not form a stable dispersion Many of the particles remain attached (aggregated) in the form of clumps, and those particles that disperse in the liquid very often clump together again to form larger aggregates that settle out of the suspension In addition, even when the particles disperse in the liquid, the dispersion may be viscous or thin, the particles may remain dispersed for different lengths of time, and the sensitivity of the dispersions to molecular environmental conditions (pH, temperature, additives) may vary greatly Before discussing the role of surfactants in these systems and the relation of the structure of the surfactant to its performance as a dispersing agent, it is necessary to review the forces between particles in these suspensions, since these forces, together with the particle size and shape and the volume of the dispersed phase, determine the properties of the suspension I INTERPARTICLE FORCES Tadros (1986) describes four types of interparticle forces: hard sphere, soft (electrostatic), van der Waals, and steric Hard-sphere interactions, which are repulsive, become significant only when particles approach each other at distances slightly less than twice the hard-sphere radius They are not commonly encountered I.A Soft (Electrostatic) and van der Waals Forces: DLVO Theory The soft (electrostatic) and van der Waals interparticle forces are described in the well-established theory of the stability of lyophobic dispersions (colloidal Surfactants and Interfacial Phenomena, Third Edition Milton J Rosen ISBN 0-471-47818-0 # 2004 John Wiley & Sons, Inc 332 INTERPARTICLE FORCES 333 dispersions of particles that are not surrounded by solvent layers) This theory was developed independently by Derjaguin and Landau (1941) and Verwey and Overbeek (1948) and therefore is called the DLVO theory It assumes a balance between repulsive and attractive potential energies of interaction of the dispersed particles Repulsive interactions are believed to be due either to the similarly charged electrical double layers surrounding the particles or to particle–solvent interactions Attractive interactions are believed to be due mainly to the van der Waals forces between the particles To disperse the particles, the repulsive interactions must be increased to the point where they overcome the attractive interactions; to aggregate the particles, the reverse must be done The total potential energy of interaction V is the sum of the potential energy of attraction VA and that of repulsion VR : V ẳ VA ỵ VR ð9:1Þ The potential energy of attraction in a vacuum for similar spherical particles of radius a whose centers are separated by a distance R is given by the expression (Hamaker, 1937) VA ẳ Aa 12H 9:2ị where A is the Hamaker (van der Waals) constant and H is the nearest distance between the surfaces of the particles ð¼ R  2aÞ when H is small ðR=a  5Þ The attractive potential energy is always negative because its value at infinity is zero and decreases as the particles approach each other In a liquid dispersion medium, A must be replaced by an effective Hamaker constant, pffiffiffiffiffi pffiffiffiffiffi Aeff ¼ ð A2  A1 Þ2 ð9:3Þ where A2 and A1 are the Hamaker constants for the particles and the dispersion medium, respectively (Vold, 1961) As the particles and the dispersion medium become more similar in nature, A2 and A1 become closer in magnitude and Aeff becomes smaller This results in a smaller attractive potential energy between the particles The potential energy of repulsion VR depends on the size and shape of the dispersed particles, the distance between them, their surface potential , the dielectric constant er of the dispersing liquid, and the effectiveness thickness of the electrical double layer 1=k (Chapter 2, Section I), where 1=k ¼ @ 4pF er e P i 11=2 Ci Zi2 A ð2:1Þ 334 DISPERSION AND AGGREGATION OF SOLIDS IN LIQUID MEDIA FIGURE 9-1 Total interaction energy curves (obtained by summation of attraction and repulsion curves) for two repulsion curves of different heights For two spherical particles (Lyklema, 1968) of radius a, when a=1=kị ẳ kaị  1, i.e., small particles and a relatively thick electrical double layer, VR ¼ er a2 20 kH e R 9:4ị When a=1=kị ẳ kaị  1, i.e., large particles and a relatively thin electrical double layer, VR ẳ er a 20  ln ỵ ekH ð9:5Þ The potential energy of repulsion is always positive, since its value at infinity is zero and increases as the particles approach each other Typical plots of VA and VR as a function of the distance H between the particles are shown in Figure 9-1, together with the plot of the total energy of interaction V, the sum of VA and VR The particles tend to aggregate at those distances where the attractive potential energy is greater than the repulsive energy and V becomes negative The form of the curve for the total potential energy of interaction V depends on the ratio of the particle size to the thickness of the electrical double layer INTERPARTICLE FORCES Potential energy of interaction (a) (b) + + 0 – P 335 – P S FIGURE 9-2 Potential energy of interaction as a function of distance of particle separation and ratio of particle size to thickness of the electrical double layer, a=ð1=kÞ ¼ ka (a) ka  1; (b) ka  a=1=kị ẳ ka (Figure 9-2), the electrolyte concentration (Figure 9-3), and the surface potential (Figure 9-4) When ka  (i.e., when the ratio of particle size to thickness of the electrical double layer is very large), the curve for V (Figure 9-2b) shows a secondary minimum (S) at a relatively large distance of separation between the particles in addition to the primary minimum (P) Particles may therefore aggregate at a relatively large distance between the particles This type of aggregation is sometimes called flocculation to distinguish it from aggregation in the primary minimum, which is termed coagulation Since the depth of the secondary minimum is rather shallow, flocculation of this type is easily reversible and the particles can be freed by agitation Particles larger than a few micrometers, especially flat ones, may show this phenomenon The effect on V of the addition of electrolyte to the (aqueous) dispersion medium and the consequent compression of the double layer is shown in Figure 9-3 With increase in the concentration of indifferent electrolyte, k increases and the energy barrier to coagulation ðVmax Þ decreases and may even disappear, consistent with the known coagulation of lyophobic colloidal dispersions by electrolyte Figure 9-4, illustrating the effect of the surface potential of the particles on V, indicates that the energy barrier to coagulation increases with increase in the surface potential The effect of adsorption of surfactant ions onto the particle surface is apparent When 336 DISPERSION AND AGGREGATION OF SOLIDS IN LIQUID MEDIA FIGURE 9-3 Influence of electrolyte concentration (as measured by k) on the total potential energy of interaction of two spherical particles Reprinted with permission from J Th G Overbeek in Colloid Science, Vol 1, H Kruyt (Ed.), Elsevier, Amsterdam, 1952, Chap 6, p 276 adsorption results in an increase in the potential of the particle at the Stern layer, the stability of the dispersion is increased; when it results in a decrease in that potential, the stability of the dispersion is lowered Since the range of thermal energies for dispersed particles may go as high as 10 kT, an energy barrier of greater than 15 kT is usually considered necessary for a stable dispersion The stability of a colloidal dispersion is usually measured by determining the rate of change in the number of particles n during the early stages of aggregation The rate of diffusion-controlled coalescence of spherical particles in a disperse system as a result of collisions in the absence of any energy barrier to coalesence is given by the von Smoluchowski equation dn ẳ 4pDrn2 dt 8:2ị 337 INTERPARTICLE FORCES FIGURE 9-4 Influence of the surface potential c0 on the total potential energy of interaction of two spherical particles Reprinted with permission from J Th G Overbeek in Colloid Science, Vol 1, H Kruyt (Ed.), Elsevier, Amsterdam, 1952, Chap 6, p 277 Since, from the Einstein equation, D ¼ kT=6pZa (equation 8.1), and r ¼ 2a, dn 4kT ¼ n ¼ K n2 dt 3Z ð9:6Þ where K0 is the rate (constant) for diffusion-controlled coalescence Experimentally determined rate constants K0 for coalescence in the absence of an electrical barrier to aggregation can be determined by adding electrolyte to the dispersion until no further rate increase is obtained (Parfitt, 1972) In the presence of an energy barrier Vmax to coalescence, dn / K0 n2 eVmax =kT ¼ Kn2 dt ð9:7Þ where K is the rate of (slow) coalescence in the presence of an energy barrier The stability W of the dispersion is defined as the ratio of the rate constants in the