WATER TRANSPORT IN LYOTROPIC LIQUID-CRYSTALS AND LIPID WATER-SYSTEMS - MUTUAL DIFFUSION-COEFFICIENT DETERMINATION

A computer algorithm based on a finite-difference method has been developed to determine the mutual diffusion coefficients for water in a contiguous series of mesomorphic phases in a monoacylglyceride-water system. The FORTRAN program based on this algorithm searches for diffusion coefficients across a phase region such that calculated phase boundary positions coincide with boundaries determined experimentally by X-ray diffraction. From the derived diffusion coefficients the phase development in time can be predicted. Another practical application is the prediction of the amount of time and water it takes to prepare samples in a defined mesomorphic phase without mechanical mixing. In the case of excess water, about 60 days is needed to transform completely a 2.5-cm-long monoolein sample initially in the fluid isotropic phase into the cubic primitive phase at 25°C. Results for the monoolein-water system give mutual diffusion coefficients ranging from 0.72 × 10-6 to 1.5 × 10-6 cm2/s in the fluid isotropic, lamellar liquid crystal, and cubic phases. These values are up to an order of magnitude lower than literature values of the self-diffusion coefficients determined by pulsed field gradient NMR for this same system. © 1990 American Chemical Society.