chapter  5
66 Pages

5

I. Introduction ................................................................ 234 II. General Points Concerning Microemulsions

Structure, Phase Behavior, and Dynamics............... 236 III. Diffusion and Rotation of Molecules and

Aggregates ................................................................... 238 A. Global Motions of the Individual Aggregates ... 238 B. Diffusion of Single Components ......................... 240

IV. Dynamics of Exchange of Surfactants and Cosurfactants............................................................... 241 A. Reminder of the Case of Simple Micelles.......... 241 B. Exchange Dynamics in Microemulsions ............ 243

V. Amphiphile Chain Dynamics, Water, and Counterions Mobility.................................................. 248 A. Motion of Hydrophobic or Hydrophilic

Chains of Surfactant Molecules ......................... 248 B. Mobility of Confined Water................................. 249 C. Mobility of Counterions ....................................... 250

VI. Percolation Phenomena and Kinetics of Droplet Coalescence ................................................................. 250 A. The Percolation Concept and Film Rigidity ...... 250 B. Effect of Temperature ......................................... 252 C. Effect of Salinity.................................................. 253 D. Effect of Additives ............................................... 256 E. Droplet Percolation and Bicontinuity ................ 257 F. Kinetics of Droplet Coalescence and

Exchange of Matter between Droplets .............. 259 G. Droplet Clustering and Rate of Exchange

between Clusters ................................................. 267 VII. Dynamic Processes Induced by an External

Perturbation................................................................. 270 A. Interfacial Dynamics and Droplet

Deformation ......................................................... 270 B. Temperature-Induced Change of Film

Curvature............................................................. 272 C. Rearrangements Following a Fast Change of

Composition: Rate of Dissolution of Excess Dispersed Phase Below the Saturation Limit... 275

D. Electric Field-Induced Dynamics of Microemulsions.................................................... 283

VIII. Implications of the Dynamic Behavior of Microemulsions in Some Specific Domains.............. 285

IX. Conclusions and Prospects ........................................ 289 References ........................................................................... 289

I. INTRODUCTION

Microemulsions, unlike classical emulsions, are usually transparent and thermodynamically stable systems requiring a significant amount of surfactant. The addition of a cosurfactant, although not always required, often appears to be necessary so that microemulsions in their simplest compositions are ternary or quaternary systems. Microemulsions are thus some sort of swollen micellar systems in which the core of the droplets accommodates a more or less important amount of dispersed oil (or water in the case of reverse micelles). Research concerning such systems, which were first mentioned by Hoar and Schulman,1 literally exploded in the late

1970s and early 1980s because of their important potential for tertiary oil recovery,2,3 in relation to their ability to produce very low interfacial tensions. Since that time, many efforts have been made to fully understand the complex nature of these systems and to explore their applications. Many types of formulations have been tested, which were accompanied by the characterization of the corresponding phase diagrams.