PERFLUOROPOLYETHER AMMONIUM CARBOXYLATES - SAXRD STUDY OF LAMELLAR LIQUID-CRYSTALS IN WATER AND FORMAMIDE

Lamellar liquid crystals of perfluoropolyether (PFPE) surfactants of r elatively short chain length (average MW 450 and 730) combined with wa ter or formamide were studied by small angle x-ray diffraction (SAXRD) for the variation of interlayer spacing as a function of solvent cont ent. The results indicated significant solvent penetration in the fluo rinated lamellae. The results give a contribution to the identificatio n of the role played on association features by the flexibility of the PFPE chain and its large volume due to side perfluoromethyl groups. A nalogies with perfluorocarbon surfactants are discussed, particularly with respect to ammonium perfluorooctanoate. The thickness of the lame llae and the area per polar head are compared in water and FA showing pronounced difference in the behavior of the liquid crystals from the two solvent systems.