Micellar networks in surfactant solutions

Surfactants are used in a wide range of applications such as detergents, paints, and pharmaceuticals. Growing environmental concerns have led industry to turn to nonionic, sugar based surfactants, such as alkyl monoglucosides, for a variety of uses. However, the presence of a miscibility gap in the phase diagrams of mixtures of longer chained glucoside surfactants in water is an industrial drawback that needs to be overcome for many applications. The goal of this thesis is to understand the interplay between the phase separation in this miscibility gap and the microstructure of the micellar solutions.; The phase behavior of alkyl monoglucosides cannot be tuned by temperature alone, but requires additives such as a second surfactant. Therefore, the molecular interactions and the self-assembly of glucosides with the ethoxylated alcohol surfactant (C10E5) and the ionic surfactant sodium dodecyl sulfate (SDS) were first investigated by microcalorimetry and compared to a molecular thermodynamic model. The glucoside miscibility gap can be closed upon addition of either SDS or C10E5 below its cloud point temperature (44.5°C), with SDS being exceptionally effective. For either ternary mixture, cryogenic transmission electron microscopy reveals the presence of a network upon approach to the miscibility gap.; In the ternary glucoside-C10E5-water mixture, for temperatures below the cloud point of C10E5, the addition of C10E5 causes the network to break up into discrete micelles and prevents phase separation. Above the cloud temperature, a micellar network forms in C10E5 alone, a mixed network forms in the ternary mixture, and there is a large miscibility gap for all surfactant ratios.; The incorporation of the ionic surfactant SDS in the nonionic glucoside aggregate introduces electrostatic repulsions that overcome the attractive forces of the micellar branch points. The small angle neutron scattering spectra show the characteristics of charged worm-like micelles in that the spectra exhibit a intensity maximum, whose position and shape vary strongly with surfactant and charge concentration. A "disordered open connected" model was used to explore the glucoside-SDS microstructure evolution, and revealed that there is increase in micellar connectivity as the phase boundary is approached.