Phase behavior and microstructure of nonionic silicone surfactants in aqueous solution

The main focus of this thesis is on understanding the aqueous phase behavior and microstructure of a series of nonionic silicone surfactants. These surfactants are known as super-spreaders for their unusual ability to promote rapid spreading of aqueous dispersions over hydrophobic surfaces. At the start of this research, the low concentration, low temperature phase behavior of these super-spreading surfactants was not fully understood. One of the goals of this thesis was to determine the phase behavior in this region and characterize its microstructure.; The phase behavior of these surfactants in dilute solution was determined. The nature of the dilute solution microstructure of the super-spreading surfactants was characterized by Small-Angle Neutron Scattering, cryogenic Transmission Electron Microscopy, and rheological measurements. These techniques show that in dilute solution the surfactant forms quite small vesicles which are easily transformed into threadlike micelles by externally applied shear.; Mixtures of similar nonionic silicone surfactants were also studied. Two surfactants were used in this study, one is quite hydrophobic, while the other is rather hydrophilic. With these two surfactants and their mixtures, the transition from a hydrophilic surfactant to a hydrophobic surfactant was studied. Cryo-TEM micrographs of the anomalous and surfactant rich isotropic phase were obtained. This work is the first time these phases have been characterized by cryo-TEM.; Other studies focused on the structure of surfactant solutions. The microstructure of isotropic, aqueous solutions of another nonionic silicone surfactant were studied by NMR self-diffusion. The transition from water-rich to surfactant-rich isotropic solution was studied. The anomalous phase was also characterized by cryo-TEM in a model system. Finally, experiments to characterize an AB block copolymer are reported. This polymer has a hydrophobic block and a large polyelectrolyte block. Its self-assembly in water and brine was studied by NMR self-diffusion and cryo-TEM.