PERFLUOROPOLYETHER CARBOXYLIC SALTS IN WATER - LIQUID-CRYSTALS BY OPTICAL MICROSCOPY AND NMR

The ammonium salts of three perfluoropolyether (PFPE) carboxylic acids differing in average molecular weight were examined for their phase b ehavior in water. Micellization was detected by surface tension measur ments, whereas lyotropic liquid crystalline phases were identified by optical miscroscopy and NMR techniques. Lamellar phases have been foun d with shorter chain surfactants (average MW of 450 and 740) while a h exagonal phase appears to form with the surfactant with the highest MW (940). Although the composition of the three PFPE surfactant mixtures certainly contributed to determine the local microstructure, the pack ing features in terms of V/al were rather clearly outlined. The increa se of the surfactant chain length and the addition of a cosurfactant o r a cosolvent produced significant variations of the self-association structures in agreement with the expected variations of the packing pa rameter.