Phase diagram and physicochemical properties of the n-octyl alpha-D-glucoside/water system

Four experimental methods were used to study the phase diagram, as well as the thermodynamic and structural properties of the binary system n-octyl alpha-D-glucoside/water in the temperature range 25-130degreesC. Sorption calorimetry allows one to determine the activity of water and enthalpy of mixing as functions of water content at constant temperature, while DSC scans temperature at constant composition and provides information on enthalpies of phase transitions. Therefore, the combination of the two calorimetric methods is a powerful too] to study composition-temperature phase diagrams. While calorimetry can be used to determine boundaries of the phases, NMR and SAXS methods are used to study their structures. A detailed phase diagram of the system is presented. A liquid crystalline cubic phase previously not reported in the system was found. The hydration in the system is endothermic, excluding the exothermic formation of hydrates. Using the sorption calorimetric method the lengths of the very short tie lines between the isotropic micellar and liquid crystalline phases were determined. Van der Waals's differential equation was used to calculate the slopes of the phase boundaries. The parameters of the lamellar, cubic and hexagonal liquid crystalline phases were determined by means of SAXS. It was found that the area per surfactant headgroup in the liquid crystalline phases varied with composition.