Thermotropic transition structures in the ternary system lecithin/isopropyl myristate/water

The ternary system lecithin/isopropyl myristate (IPM)/water passes through a reversible phase transition from a lamellar liquid crystal to a reverse micellar solution (RMS) while heated. The effect of water content and temperature on the phase transition is subject to this study. In order to determine the phase transition temperature (PTT), the disappearance of distinct diffraction peaks in small-angle X-ray diffraction (SAXD) is interpreted as a complete phase transition from a structured liquid crystalline phase into a non-structured RMS. In addition to SAXD, polarization microscopy and transmission electron microscopy (TEM) were employed to characterize the structure of the mesophases. The RMS, which exists at temperatures above the PTT was examined by means of diffuse small-angle X-ray scattering (SAXS). The PTT is found to increase with increasing water content. With small amounts of water and at comparably low PTTs, an additional structure besides the lamellar liquid crystal could be observed. Further investigations lead to the conclusion that this structure is a thermotropic transition structure most probably of a cubic type. (c) 2005 Elsevier B.V. All rights reserved.