Phase Diagrams, Microstructure and Phase Separation in Alkyl Glucoside Systems

Abstract: The aim of this thesis work was to study phase diagrams, microstructure and phase separation in alkylglucoside systems. Both alkyl glucoside/water systems and microemulsions with alkyl glucosides have been studied. The phase diagram of the ternary n -nonyl-beta-glucoside (C₉G₁)/ n -decyl-beta-glucoside (C₁₀G₁)/water system has been determined and is discussed in relation to the binary C₉G₁/water and C₁₀G₁/water phase diagrams. The evolution of the microstructure has been determined by means of NMR diffusometry along dilution lines through the micellar region of the ternary phase diagram. It was found that the phase separation, observed in the dilute C₁₀G₁ rich region of the C₉G₁/C₁₀G₁/water phase diagram, is due to differences in the networks in different regions of the phase diagram. Networks rich in C₉G₁ are more likely to undergo scissions and breaks apart more easily, whereas the network rich in C₁₀G₁ are less likely to have scissions and thus deal with dilution stress by separation into two phases. The phase behavior in the water/ n -octane/ n -octyl-beta-glucoside (C₈G₁)/1-octanol system together with the four ternary phase diagrams of the system have been studied. The tuning parameter for curvature in the quaternary alkyl glucoside microemulsion systems is not the overall 1-octanol content but the volume fraction of 1-octanol in the amphiphilic film. The types of microstructures formed along the trajectory of the middle-phase have been examined by NMR diffusometry. The diffusion measurements provide clear evidence of the transition from oil-in-water to water-in-oil microemulsions via bicontinuous structures in a remarkably large range around phase inversion. A novel phase separation into two coexisting concentrated micellar solutions has been discovered in the ternary water/C₈G₁/ n -octane system. Finally, further evidence for the presence of branched micelles in the alkyl glucoside/water systems is presented from NMR diffusometry applied to n -octane as a probe in the C₈G₁/water system.