Release studies from lyotropic liquid crystal systems.

A temperature-composition diagram of systems containing the nonionic surfactant polyoxethylene (20) isohexadecyl ether (1) and water was established. Three different anisotropic areas existed over the concentration range 33-80% of 1. Release of salicylic acid from liquid crystalline phases of 1 into aqueous buffer across lipoidal barriers was also studied. Rates of transfer as a function of percent loading from a neat mesophase containing 37% of 1 and also from systems with different molecular packing were determined. Apparent activation energies of transfer from an ordered solvent containing 37% of 1 and from an isotropic medium of the same chemical composition were found to be 33.3 and 9.4 kcal/mol, respectively. These findings suggest a pronounced effect of medium structure on the interfacial resistance of the barrier.