Fabrication and Properties of Asymmetric Fluorinated Polyimide Membrane with High Gas Permeability

Abstract

The control of gas transport though polymer membranes is of primary concern in the development of new gas separation membranes. Here, a new possibility for gas separation is presented using an asymmetric fluorinated polyimide membrane with an ultrathin and defect-free skin layer. The structure of the asymmetric membrane fabricated by a dry/wet phase inversion process showed an ultrathin skin layer and sponge-like structure characterized by the presence of macrovoids. We have prepared a series of asymmetric membranes with different skin layer thicknesses from 10 to 5.0 × 10³ nm by the dry/wet phase inversion. Four gas permeances through the asymmetric membrane decreased in the order, CO₂ > O₂ > N₂ > CH₄, and the trend was in accordance with the kinetic diameter of gas molecules. The gas selectivity of the asymmetric membrane increases with a decrease in the surface skin layer thickness, which may be due to the fact that the surface skin layer of the membrane with a thinner thickness forms a more packed structure.