The following section summarizes the key contributions of the research presented in this thesis, in the areas of surfactant property prediction, microemulsion formulation, and micellar stability. More specific conclusions can be found at the end of chapters 2-4 for the above subjects, respectively.

Surfactant property prediction. The ability to predict properties from molecular structure alone can be a powerful tool, both for prediction of properties of compounds not yet synthesized, and for tailoring molecules to achieve certain properties. The descriptors chosen in such quantitative relationships also may reveal the aspects of molecular structure influencing the property of interest. Over the last 20 years, hundreds of molecular descriptors have been developed for predicting various chemical and physical properties. In this thesis, these descriptors have been applied to the prediction of predicting surfractant properties, for the first time. Excellent results were achieved for the prediction of CMC, cloud point and Krafft point for diverse sets of surfactants.

Microemulsion formulation. Microemulsions have wide application in industry and consumer products. The microemulsions considered here are special, as they are made from mixtures of nonionic surfactants, using no cosurfactant that may not be suitable for cosmetic applications, thus increasing the difficulty of the formulation work. Presently the means of designing new microemulsions for a specific purpose is a trial and error process of surfactant selection for given oil and aqueous phases. In this thesis, rules are developed to narrow the trial and error search process, by providing some guidelines for the design of water-in-oil microemulsions. The utility of HLB is demonstrated for the first time, as a tool for w/o microemulsion design.

Micellar stability. Micelles are aggregates of surfactants in aqueous solution. They are essential for most of the processes that use surfactants, as they allow the creation of a hydrophobic domain in an otherwise aqueous environment. Micelles are not static structures, but rather are dynamic, constantly disintegrating and reforming. In this thesis, new research progress has been made on several related fronts. The influence of additives (electrolyte, nonionic surfactant, alcohols, cosolvents) on anionic surfactant micellar stability is investigated. The influence of micellar lifetime on processes is studied. The stability of cationic micelles is studied at higher concentrations than previously reported. A comparison between some technological processes (fabric wetting, foamability) and cationic surfactant micellar stability show that the relationships drawn from anionic surfactant studies may not apply to cationic surfactants. Finally, methods for measuring the micellar stability of nonionic surfactants are investigated. The detection method used in ionic surfactant lifetime studies, namely solution electrical conductivity, cannot be used for nonionic surfactants. Alternative detection methods, such as the use of solvatochromic dyes to probe the polarity of the micellar interior, coupled with light absorption detection, are potentially usable. A light absorption method without dye is possible, if absorption measurements are made in the ultraviolet region of the spectrum, where size changes in the micelles can be detected by changes in the Rayleigh scattering losses. Either of these techniques, coupled with a rapid temperature-jump of the sample, should allow the measurement of nonionic surfactant micellar lifetime.

The following research ideas are possible future projects that are a direct continuation of the work performed in this thesis.

Surfactant property prediction. 1) A new set of descriptors has been developed by Kier and Hall, called the electrotopological indices, which were designed to better handle polar interactions. The surfactant structure-property correlations should be tried with these new descriptors. 2) Data is available for cationic and zwitterionic surfactant CMC, and these should be investigated. 3) By examining possible groupings of surfactant classes for CMC prediction, it may be possible to make more general equations than those limited to each of the classes. 4) Additional surfactant property data can be gathered and analysed using the QSPR approach. 5) It would be interesting to analyse the results obtained with correlations developed using a training set consisting of most of the compounds, testing the errors in a test set to see how general the regressions are. 6) It would be interesting to study the development of rules for surfactant mixture properties. The nonlinear nature of such mixture properties may be predictable.

Microemulsions. Several interesting microemulsion formulation problems exist, that remain unsolved. 1) Microemulsions with triglyceride oils are poorly understood, and no examples of highly solubilizing microemulsions exist. Such microemulsions would be valuable for pharmaceutical applications. 2) Microemulsions formed with lecithin as a surfactant are of interest, also with pharmaceutical applications. 3) More work can be done to map out the mixture phase diagrams beyond the microemulsion phase region. 4) The temperature dependence of nonionic microemulsion solubilization should be studied.

Micellar stability. There is still relatively little research done on micellar stability, and many opportunities for projects exist. 1) Additional work on the relationship between micellar lifetime and technological processes for cationic surfactants needs to be done to address the differences between these relationships and those seen for anionic surfactants. 2) It would be very interesting to build an apparatus to measure nonionic temperature-jump using absorption detection, as nonionic micellar lifetime is essentially unmeasured. 3) Solvatochromism in micellar solutions should be investigated, as certain dyes are potentially useful probes of micellar changes.