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

Abstract

Aqueous mixtures of the two alkyl glucosides n-nonyl β-glucoside (C9G1) and n-decyl β-glucoside (C10G1) have been studied. The phase diagram of the ternary C9G1/C10G1/water system in the water rich corner has been determined and is discussed in relation to the binary C9G1/water and C10G1/water phase diagrams. The latter two diagrams are significantly different in the dilute surfactant regime with a broad two-phase region in the C10G1/water system that is not present in the C9G1/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 C9G1/C10G1 ratio is varied and at constant C9G1/C10G1 ratio when the total surfactant concentration is varied. From the results presented, it is suggested that the microstructure in the solution phase of the C9G1/C10G1/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 C10G1/water system is also proposed and discussed.