On structural relations between lipid mesophases and isotropic reversed micellar (L2) solutions

Abstract

The structural relations in lipid systems between liquid crystalline and isotropic liquid L2 phases have been studied by low-angle X-ray diffraction for two-model systems, viz. sodium octanoate/decan1-of/water and soybean lecithin/soybean oil/water. A transition between the two states may be obtained either by a change in temperature or in composition. The low-angle X-ray scattering curve for the liquid L2 solution shows a maximum with the same angular position as the innermost reflection given by a coexisting liquid crystalline phase, and the integrated intensities for the scattering maxima are almost the same. The relative amounts of ordered structural units are thus about the same on both sides of the transition. A close resemblance in the structures of the reversed micellar aggregates in the L2 solution and the liquid crystalline phase is thus proposed. If the liquid crystalline phase possesses a reversed hexagonal structure its long-range two-dimensional order will be replaced by a “medium” range order in the liquid phase but the latter will basically have the same hexagonal arrangement with the difference that the polar rod aggregates are short. If the liquid crystalline phase has a lamellar structure there will be a reduction in the size of the bilayer domains and an increase in their curvature.