PHYSICAL-CHEMICAL PROPERTIES OF THE N-OCTYL BETA-D-GLUCOSIDE WATER SYSTEM - A PHASE-DIAGRAM, SELF-DIFFUSION NMR, AND SAXS STUDY/

The n-octyl beta-D-glucoside/water binary phase diagram (temperature v s concentration) and the aggregation parameters of the individual phas es have been determined. n-Octyl beta-D-glucoside forms four different phases together with water. At temperatures below 22 degrees C, there is an isotropic solution region from neat water extending up to almos t 60 wt % n-octyl beta-D-glucoside. As the concentration is further in creased, three liquid crystalline phases form in the following order: hexagonal, cubic, and lamellar. At high surfactant concentrations (>93 wt %) the lamellar phase is in equilibrium with hydrated crystals. Th e hexagonal phase disappears at temperatures slightly higher than 20 d egrees C. The solution region has been investigated with H-1-NMR to de duce the self-diffusion coefficients of both n-octyl beta-D-glucoside and water. From these results it has been possible to draw conclusions about the surfactant aggregation behavior at dilute concentrations an d when the n-octyl beta-D-glucoside concentration is increased. The wa ter diffusion in the n-octyl beta-D-glucoside/water system has been co mpared with the diffusion process of water in a glucose solution, and it has been possible to interpret the data in terms of water diffusion in a glucose solution with some additional obstruction effects from t he micellar hydrocarbon cores. The liquid crystalline phases have been examined by means of small-angle X-ray scattering and analyzed in ter ms of repetition distances and area/head group in the hexagonal, cubic , and lamellar phases. An important result of this study is the fact t hat the area per glucose unit in the surfactant is an almost invariant quantity across the phase diagram.