ELECTROCHEMICAL SYNTHESIS OF ULTRATHIN FILM COMPOSITE MEMBRANES

We describe in this paper a new method for forming ultrathin film composite membranes; such membranes might be useful for gas (or other) separations or as separators in electrochemical cells. In general, ultrathin film composite membranes consist of an ultrathin (less than ca. 2.0-mu-m) polymer skin coated onto the surface of a microporous support membrane. The support membrane provides the requisite mechanical strength but, because of its porosity, does not significantly retard the flux of permeate through the composite. The desired separation occurs in the ultrathin polymer skin; because this skin is thin, flux through the composite can be high. Ultrathin film composites can, in principle, provide high flux, good selectivity, and good mechanical strength. This combination of properties would be nearly impossible to obtain with a homogeneous membrane. The method described here entails electrochemically-initiated polymerization of the ultrathin polymer skin at the surface of a microporous alumina support membrane. The films synthesized and investigated here were composed of a crosslinked styrenic polymer. We have investigated the mechanism of the film formation process and the effects of various experimental parameters on the thickness of the polymer film obtained. We also present results of gas-transport studies on these new composite membranes. These studies show that defect-free composite membranes can be obtained via this new electropolymerization method.