Effect of solvent exchange on the morphology of asymmetric membranes

Abstract

The effect of solvent exchange and the subsequent drying process on membrane morphology was investigated for microporous and integrally-skinned asymmetric membranes by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For the microporous membranes, significant changes in morphology and transport properties were observed due to the collapse of micropores in the top skin layer. In the case of integrally-skinned asymmetric membranes, only negligible differences in membrane structure were observed upon solvent exchange. The effects of solvent exchange depend strongly on the capillary forces imposed on the membrane matrix by a liquid present in the membrane pores. A membrane dried using supercritical CO2 experienced no capillary forces upon drying, and, hence, the membrane morphology observed by SEM showed the nascent, original membrane structure formed by the phase inversion process.