Physical−Chemical Properties of C9G1 and C10G1 β-Alkylglucosides. Phase Diagrams and Aggregate Size/Structure

Abstract

The temperature versus concentration phase diagrams of the n-nonyl β-glucoside/water and the n-decyl β-glucoside/water systems are presented. The micellar region of the n-nonyl β-glucoside has been studied using 1H NMR self-diffusion to obtain information about the micellar size. Nonspherical aggregates are formed at concentrations immediately above the cmc. Three different liquid crystalline phases are formed as the concentration of n-nonyl β-glucoside is increased, viz. a hexagonal, a bicontinuous cubic (of space group Ia3d), and a lamellar phase. 1H NMR self-diffusion measurements have also been performed across the phase boundary separating the micellar and the cubic regions. It was found that there is no discontinuity in the surfactant self-diffusion when crossing this phase boundary. A particular feature of the n-decyl β-glucoside is the occurrence of a phase separation into two liquid isotropic solutions in the (total) surfactant concentration interval from approximately 0.1 to 17 wt % surfactant. The dilute and concentrated solutions have been examined by means of time-resolved fluorescence quenching (TRFQ). It was found that, at the lower phase boundary, nonspherical discrete aggregates are formed, whereas at the upper phase boundary (17 wt %), the aggregates are large. At high surfactant concentration (>65 wt %), a lamellar liquid crystalline phase is formed. The liquid crystalline phases present in the two binary phase diagrams have been characterized by small-angle X-ray scattering (SAXS). The results have been analyzed in terms of repetition distances and surfactant head-group areas. An important result from the SAXS analysis is that the head-group area is an almost invariant parameter in the different liquid crystalline phases.