MEMBRANE STRUCTURES OF AQUEOUS FLUORINATED NONIONIC SURFACTANTS

Fluorinated non-ionic surfactants may form aqueous phases of fluid membranes, given their marked hydrophobic character. Depending on the temperature and/or the concentration, they self-associate into a lamellar liquid crystalline phase L(alpha), a sponge phase L(3), Or dilute dispersions of membranes whose exact structure is not well known. These systems have been studied by X-ray, neutron and light scattering/diffraction, and electrical conductivity measurement. At higher dilution the position of the Bragg peak no longer changes with concentration and thus the true thermodynamic limit of the phase can be determined. Measurement of the excess of membrane area relative to thermal fluctuations of curvature allows the evaluation of the rigidity constant as a function of temperature. In addition, a study of the kinetic evolution of the mixtures L(alpha)/water (plus monomers) clearly reveals a metastable character of the intermediate structures, which change with time. From a study of the L(3) structure, an interpretation of the data is made in terms of a tetragonal local order. Finally, some results are presented on ''vesicles'' that are formed by sonication of the membrane dispersions; it should be emphasized that these vesicles are composed of short single-chain non-ionic surfactants.