The mechanism of formation and the structure of microemulsions

The subject of this dissertation is the formation and structure of microemulsion systems. At the initiation of this dissertation there was some disagreement as to whether microemulsion systems are thermodynamically or kinetically stable systems. We assume that each one of the microemulsion systems investigated in Chapter 2 and 3 are thermodynamically stable systems. Once this assumption was postulated, the thermodynamic properties associated with microemulsion formation were determined for each microemulsion system investigated. For each system investigated in Chapter 2 and 3, the change in free energy associated with microemulsion formation are small negative numbers. This shows that the process is spontaneous for each system investigated. However the driving force in transforming an emulsion into a microemulsion is small. Therefore we conclude that the microemulsion systems prepared by the titration method in Chapter 2 and 3 are thermodynamically stable systems.;The remainder of this thesis is dedicated to investigating the size and structure of the microdroplets in oil-in-water microemulsion systems. In Chapter 4 the size of the microdroplets is measured by the technique of D.C. polarography. This technique depends on tagging the microdroplet with an oil soluble electroactive probe and measuring the diffusion current of this reducible species. Microdroplet radii were found to increase as the volume fraction of dispersed phase (oil) increased for the oil-in-water microemulsion systems and prepared at constant amount of primary surfactant and investigated by D.C. polarography.;In Chapter 5 the size of the microdroplets in two different oil-in-water microemulsion systems is measured by vapor pressure measurements. From the vapor pressure measurements two different regimes of phase behavior are found for these systems. One region occurs at low volume fraction of dispersed phase and the phase behavior is characterized by a vapor pressure lowering in this region. The microdroplets can be described as isolated and noninteracting particles in the low dispersed volume fraction region. At high volume fraction of dispersed phase the microdroplets in these systems begin to interact and the vapor pressure increases dramatically.