Phase behavior, formation, and rheology of cubic and hexagonal phase based gel emulsions in water/tetraglyceryl lauryl ether/oil systems

Abstract

The phase behavior, formation, and rheology of the cubic (O/I 1) and hexagonal (O/H 1) phase based gel emulsions have been reported in water/tetraglyceryl lauryl ether/oil systems. It has been found that the phase sequences in the ternary phase diagram are not considerably changed with different oil but the oil solubilization capacity varies a little extent in each phase. It has been observed that the I 1 phase induced in the phase diagram due to the solubilization of oil in the micellar (W m) or hexagonal (H 1) phase in both the systems, which could solubilize small amount of oil. After the solubilization limit, the excess oil is in equilibrium with the H 1 and I 1 phases in the two-phase region, allowing the preparation of the O/H 1 and O/I 1 gel emulsions. Though, the O/I 1 gel emulsion could form at higher concentration of oil compared to the O/H 1 gel emulsion but both gel emulsions show prolonged stability, i.e., oil did not separate within 2 months. In rheology, highly elastic gel-like properties of the I 1 phase have been observed but the viscous modulus ( G″) show minima at higher frequency. The H 1 phase shows weak gel properties where the elastic ( G′) and the viscous ( G″) moduli vary with frequency. In both the O/I 1 and O/H 1 gel emulsions, the rheogram show elastic nature ( G′ > G″) and the G′ is nearly frequency independent. It is also found that the complex viscosity, | η*| increases in single phase (I 1 and H 1 phase) but decreases in the related gel emulsions with increasing oil concentration. All samples show shear thinning behavior but plateau region were not seen at lower frequency. Increasing the values of the | η*| could be ascribed with the interaction of the neighboring micelles whereas decreasing tendency in the gel emulsion relates to the volume fraction of the continuous phase in the system.