Structure of cubic phases in ternary systems Glucopone/water/hydrocarbon

Abstract

Phase diagrams for the ternary systems of Glucopone, water and several hydrocarbons are reported. Four different types of hydrocarbon are used namely; heptane, octane, dodecane and tetradecane. Small angle X-ray scattering (SAXS) and polarizing microscope are used for phase identification and structure characterization. The ternary systems are shown to form different liquid crystalline phases with the increase of concentration in the following order—cubic, hexagonal, and lamellar. The liquid crystalline phases present in the ternary phase diagrams have been characterized by SAXS and further analyzed in terms of lattice parameters and area per surfactant head-group. An optical isotropic gel phase with strong elastic properties is found in these systems and identified as cubic phase. The cubic phase is optically isotropic, transparent and highly viscous phase with three-dimensional structure. The cubic samples showed several diffraction peaks and can be assigned to the Ia3 d space group. The rheological study on the cubic phase is performed. All cubic samples behave as solid-like material with storage modulus G′∼0.7×10 6 Pa typical of cubic lyotropic materials. The effect of the oil concentration and oil types on the storage and loss moduli for the cubic liquid crystalline phases is examined. For all systems, the elastic modulus and the complex viscosity are found to increase with oil concentration while decrease with increasing the length of hydrocarbon chain. Tetradecane ternary system shows completely opposite behaviors. The elastic modulus decreased when the oil content is increased. The effect of temperature on the dynamic moduli of the systems is also studied. The systems show very sharp melting transition. Both, storage and loss modulus are found to decrease as the temperature increased. It was possible to deduce the influence of the alkane chain lengths in the phase and rheological behaviors of the Glucopone surfactant. Generally, the ternary systems show similar rheological behaviors except for tetradecane system, which found to show completely opposite behaviors. The cubic phase region is found to shift to higher oil content with the increase in the alkane chain length of hydrocarbon. Finally, it is worth to mention that no cubic phases are found with toluene and cyclohexane as oil phase.