Perfluorosulfonated ionomer membranes (Nation (R)) were modified by a chemical treatment to increase the permeability of membrane structures. The treatment consisted of a single phase propylene carbonate-water mixture which, in the presence of the sulfonic acid groups of the Nation (R), yielded CO2. This CO2 presumably expanded having the effect of creating larger pores within the Nafion (R) framework. The resulting membrane had filtration characteristics in the ultrafiltration-microfiltration range with a maximum flux of similar to 10kg m(-2) h at 1.3782 x 105 Pa (20 psig). These structures were characterized using flux, solute rejection, neutron scattering and water volume measurements. Further, these membranes were found to be suitable for emulsion separations with the water phase permeating through the membrane. In preliminary results, a water-xylene mixture exhibited a single phase permeate with approximately 60% of the flux of pure water. (c) 2006 Published by Elsevier B.V.