My years of research at the University of Florida have brought me down many interesting paths in the field of interfacial phenomena. In this thesis, I hope to pass on what unique observations I have made along the way. My contributions to this field of interfacial phenomena lie in three areas, with surfactant physical properties as the binding theme. These three areas are microemulsion formulation, ionic surfactant micellar lifetime, and surfactant structure-property relationships.

Thesis organization. This thesis contains three separate projects, as described in the abstract section, tied together by the common thread of the prediction of properties in surfactant systems.

Structure-property relationships. In the first section, surfactant structure-property relationships are investigated. The approach used has been successfully applied by chemists to physical properties of compounds (QSPR), and also by biologists and medicinal chemists to drug activity (QSAR). The validity and success of this method has led to the publication of at least two journals in this field, JCICS and QSAR. The group of Professor Katritzky in the Department of Chemistry have developed a powerful tool (CODESSA) to assist the scientist in finding such relationships. It is surprising to note that the QSPR approach has never been applied to surfactant chemistry. This thesis and associated publications [Huibers et al. 1996b; 1996c; 1996d] are the first attempts of applying QSPR to surfactants.

Microemulsions. In the second section, synergism in nonionic surfactant mixtures is studied, specifically applied to enhancing water solubilization in water-in-oil microemulsions. Much work has been done in this area by many researchers, examining microemulsions made from many different oils and surfactants, and in the introduction to this section the relevant work on nonionic microemulsions and attempts at design rules for microemulsions are extensively reviewed. For certain food and pharmaceutical applications, microemulsions without cosurfactants are desirable. There is hardly any literature on w/o microemulsions using only nonionic surfactants. In this thesis, the rules of w/o microemulsion formulation using mixtures of nonionic surfactants are clarified, and numerous examples of such microemulsions are presented.

Micellar stability. In the third section, micellar stability is investigated. Micellar stability has been shown to influence numerous technological processes involving surfactant solutions. Also, the effects of additives to the surfactant solution on the micellar stability have been studied. This thesis extends the knowledge of the effects of additives on the model anionic surfactant system, SDS. The micellar stability of cationic surfactants at high concentrations is studied for the first time, along with the effect of cationic micellar stability on some technological processes. There is no established technique for the measurement of nonionic micellar lifetime. The potential of two possible detection techniques are investigated; 1) spectral absorbance shift in solvatochromic dyes, and 2) UV Rayleigh scattering in the 200-220 nm region. Both of these techniques may be used as detection methods for a temperature-jump perturbation. The magnitude of potential changes by these two methods as a function of temperature is presented.