Phase Separation and Aggregate−Aggregate Interactions in the C9G1/C10G1 β-Alkyl Glucosides/Water System. A Phase Diagram and NMR Self-Diffusion Study

Aqueous mixtures of the two alkyl glucosides n -nonyl β-glucoside (C 9 G 1 ) and n -decyl β-glucoside (C 10 G 1 ) have been studied. The phase diagram of the ternary C 9 G 1 /C 10 G 1 /water system in the water rich corner has been determined and is discussed in relation to the binary C 9 G 1 /water and C 10 G 1 /water phase diagrams. The latter two diagrams are significantly different in the dilute surfactant regime with a broad two-phase region in the C 10 G 1 /water system that is not present in the C 9 G 1 /water system. The evolution of the microstructure in the micellar solutions has been determined by means of NMR self-diffusion measurements both at a constant total surfactant concentration when the C 9 G 1 /C 10 G 1 ratio is varied and at constant C 9 G 1 /C 10 G 1 ratio when the total surfactant concentration is varied. From the results presented, it is suggested that the microstructure in the solution phase of the C 9 G 1 /C 10 G 1 /water system changes from discrete micelles at low concentrations toward a bicontinuous structure of interconnected rods as the concentration increases. A mechanism behind the phase separation in the C 10 G 1 /water system is also proposed and discussed.