Chairman: Dr. Dinesh O. Shah
Major Department: Chemical Engineering

A greater knowledge of the physical properties of surfactants is important to future applications of new surfactants, as well as for improvements in product development with currently available surfactants. In this thesis, three areas are examined; (i) the development of unique new surfactant quantitative structure-property relationships (QSPR) using the latest advances in chemical topological indices and semi-empirical quantum-chemical calculations, (ii) synergism in mixtures of nonionic surfactants for the formation of optimum microemulsions, and (iii) additive effects on ionic surfactant micellar lifetime and the effect of micellar lifetime on processes of technological interest.

The ability to predict physical and chemical properties given only surfactant molecular structure has great potential in the screening of new surfactants for new applications. Molecules can even be considered that have not yet been synthesized. Modern QSPR techniques have not previously been applied to surfactants. A wide variety of molecular descriptors have been screened against surfactant physical properties. Correlations are presented for critical micelle concentration, cloud point, Krafft point, and molecular volume as applied to surfactant tails.

Microemulsions have applications in such diverse areas as foods, pharmaceuticals, and nanoparticle synthesis, among others. It is desirable to be able to solubilize the maximum amount of the inner phase into the bulk liquid phase, using a minimum of surfactant. Synergism is possible by using surfactant mixtures, improving solubilization results over any single surfactant, in creating water-in-oil microemulsions. Rules for surfactant selection based on HLB, molecular ratio, and influence of oil phase are presented.

Micellar stability has been shown to influence many processes of technological importance, including foaming, fabric wetting, emulsification, etc. Any process where surface or interfacial tension is important, and new interface is being rapidly created, will be influenced by micellar stability. As no practical surfactant system uses pure surfactant, the influence of alcohols, glycerol, electrolytes and nonionic surfactants on sodium dodecylsulfate micellar lifetime is examined. Measurements of micellar lifetime were made for several cationic surfactants, as well as a comparison of lifetime to processes such as fabric wetting and foamability.