PHASE-INVERSION MEMBRANES - CHARACTERIZATION OF PATTERNS OF SKIN HOLES

The statistical structure of the two-dimensional random pattern of holes which are formed through the skin of phase-inversion membranes is analysed. Membranes were prepared from a polyetherimide solved in N-methyl-2-pyrrolidone; solutions were quickly immersed in water, at room temperature. The random pattern was observed with videomicroscopy; it is shown that it can be described quantitatively from the analysis of the ensemble of all quadrilaterals drawn from nearest neighbouring holes. Perimeters and areas of quadrilaterals were found to obey a log-normal probablility distribution function. Several features characterize the random pattern of holes. i) There is a characteristic minimum distance between nearest neighboring holes; its order of magnitude is 5 mu m. ii) This distance is shortened when the polymer concentration in the casting solution is increased. iii) This distance is lengthened when the solvent concentration in the coagulation bath is increased.