Rheological properties of lamellar liquid crystals formed in Brij97/castor oil/water systems in the presence of soybean lecithin

Abstract

Phase diagrams of Brij97/castor oil (COil)/water in the presence of soybean lecithin (SL) have been determined at 37 ^oC. The lamellar phases have been investigated by polarizing optical microscopy, rheological technique and small angle X-ray scattering. With increasing SL content, the domain of the lamellar phase extends to higher COil concentration. At constant surfactant concentration, the shear viscosity increases for samples containing more SL. The storage modulus<i style="mso-bidi-font-style:normal"> G</i>' increases on addition of SL and reaches a maximum in the SL/COil/water system, with the smallest area of surfactant molecules at the interface. For the Brij97/SL (1:3) system, at a fixed ratio of COil/water, the dynamic moduli increases with increasing surfactant concentration. At 37 ^oC, the Brij97/SL (1:1)/water/oil systems with ethyl oleate and COil have a higher moduli and smaller <i>a_S</i> than with isopropyl myristate. The values of activation energy of ethyl oleate and COil systems are larger than that of isopropyl myristate system, indicating that the network in lamellar phases in ethyl oleate and COil systems are stronger than in the isopropyl myristate system.