MICROEMULSIONS AND THEIR RELATION TO SWOLLEN MICELLAR SOLUTIONS

The thermodynamic stability of microemulsion systems and their relation to swollen micellar solutions have been investigated. The results obtained suggest that the apparent path-dependent properties sometimes observed during microemulsion formation may be explained by the small free energy values involved in transforming an emulsion into a microemulsion. These results suggest that the right order of mixing the various components plays a major role in lowering the activation energy barriers these systems must overcome during their formation. Based on these results it is concluded that microemulsions are thermodynamically stable systems.;During the titration of the emulsions with a cosurfactant, just before clearing, the system undergoes viscosity changes due to the formation and resolution of filament structure into microdroplets. After each addition of cosurfactant, systems prepared with a constant amount of water, oil and surfactant were allowed to equilibrate and phase separation was observed. From these results it is concluded that O/W microemulsions may be described as hydropathic oleomicellar solutions.;The vapor pressure of five O/W microemulsion systems was determined as a function of increasing the volume of hydrocarbon in the dispersed phase using an isoteniscope. At low volume fractions of hydrocarbon, the microemulsion droplets behave like large molecules in solution. Beyond a certain hydrocarbon volume fraction, the droplets are less stable. The energy of activation corresponding to the breaking of the interfacial sheath was found to be between 35.2 and 20.9 kJ/mole. (Abstract shortened with permission of author.).;Emulsions (5 o/w; 1 w/o) prepared with oil, water and surfactant were titrated to clarity with a cosurfactant. The volume of the continuous phase was varied from 10 to 60 ml. The mole fractions of cosurfactant/surfactant and cosurfactant/continuous phase was determined at various temperatures (15 to 55(DEGREES)C). At 30(DEGREES)C, free energy and enthalpy changes accompanying cosurfactant adsorption during microemulsion formation were found to vary from -19.6 to -6.4 kJ/mole respectively. Entropy of formation changes were found to be positive in 5 cases from 3.5 x 10('-2) to 8.3 x 10('-2) kJ/K mole and in one case negative -1.8 x 10('-2) kJ/K mole. These results indicate that microemulsion formation is a spontaneous process, however the driving force is small. O/W emulsions of long chain sulfate/n-hydrocarbon/5% NaCl were titrated to clarity (85% transmittance or better) with long chain dimethylamine oxide.