Transition in porous morphology of PEI membrane

Structure transition, an important feature of membraneforming systems, is appeared if a casting thickness of polymer solution is placed in the critical region, transferring finger-likestructure to a sponge-like one or vice versa [1]. A few works have been done to investigate the effect of casting filmthickness or the spinneret diameter on the morphology[1-3]. Vogrin and colleagues have reported a structural transition (finger-to-sponge like structure) with respect to the thicknessof the membrane in the cellulose acetate/acetone/water system. The results of their work show that the structuretransition occurs between 300 and 500 μm. Stropnik and colleagues have measured the turbidity and shrinkage of several systems in thicknesses of 150 and 300 μm. They alsocharacterized the membranes by measuring pure water permeability. Different behaviors of the same material withdifferent thicknesses of membranes are proof of morphology variation. More observations on the evolution of structure during the process have been presented by Azari et al [1]found the membrane thickness as the key parameter for controlling the macrovoid structure. Polyetherimide (PEI) isone of the interesting polymers that has been widely used as a membrane material for gas filtrations[4]. PEI also has a potential for chemical reactions which help to improve its surface properties. The aim of this research is to investigate the structural properties of PEI membranes fabricated with different thicknesses