Skinned polymeric membranes. Approach to the mechanism of formation of surface holes

It is shown quantitatively that the formation of holes through the skin of membranes, prepared by the quick immersion in water of polyetherimides in solution in N‐methylpyrrolidone, is governed by the solvent mobility. The surface pattern observed by videomicroscopy exhibits a characteristic distance between neighbouring holes (≃5 μm) which is a linear function of D−1s; Ds is the solvent diffusion coefficient in the polymeric solution, measured using a pulsedfield gradient NMR technique. The dependence of this distance on the solvent concentration in water is also characterized.