Effects of solute characteristics and concentration on a lyotropic liquid crystal: solute-induced phase change.

We investigated the effects of increased concentrations of the solutes, salicylic acid, benzoic acid, and o-, m-, and p-methoxy benzoic acids, on the anisotropic properties of a liquid crystal solvent. The lamellar liquid crystal was composed of 37% polyoxyethylene (20) isohexadecyl ether in aqueous buffer of pH 1. Phase change, transition temperature, refractive index, and specific resistance of the mesophase were studied in the presence of solutes. Transfer rates of the solutes from the bulk mesophase into aqueous buffer across a lipoidal barrier were used to determine their apparent permeability coefficients. The results indicate that a phase change occurred in the liquid crystal from a lamellar to a hexagonal structure, in the case of salicylic, benzoic, and m-methoxy benzoic acids. However, o- and p-methoxy benzoic acids showed no effect on the packing arrangement of the liquid crystal in the concentration range studied. The occurrence of the phase change was both solute and concentration dependent. Relative values of apparent permeability coefficients of solutes reflected the extent of solute-solvent interactions in the systems.