Morphology evolution of thickness-gradient membranes prepared by wet phase-inversion process

In this paper, the thickness-gradient membranes defined as flat sheet membranes with an increasing membrane thickness were prepared using polyetherimide (pei)/n-methyl-2-pyrrolidone (nmp)/gamma-butyrolactone (gbl) casting solutions with the same polymer concentration (15 wt% pei) and two different ratio of nmp/gbl by wet phase-inversion process. with an increase in membrane thickness, the membrane morphology evolution from sponge-like to finger-like structure was investigated clearly, and it was described with the critical structure-transition thickness (l-c) and general sponge-like structure thickness (l-gs). the morphology evolution of thickness-gradient membranes was illustrated with three different thickness regions. (c) 2008 elsevier b.v. all rights reserved.