PORE SIZE DISTRIBUTIONS OF TRACK-ETCHED MEMBRANES; COMPARISON OF SURFACE AND BULK POROSITIES

Abstract Here we compare surface and bulk porous morphologies for several track-etched membranes. The experimental techniques include approaches with different proper supplementary pore size ranges. In order to analyze bulk porosities we used: a mercury intrusion apparatus, an extended bubble point method and a gas adsorption–desorption technique which allows to detect pores with decreasing sizes. Referring to the surface structure, scanning electron and atomic force microscopies have been used. Finally, a solute retention method has been used to evaluate pore size distributions from operative conditions of operation. In particular from a comparison of bulk and surface pore size distributions, it is noted that permeability is really determined by the bulk pore size distributions as shown for several track-etched membranes. For these membranes, pore entrance sizes are narrower than those determined by permeability which in turn agree with the bulk pore size distribution. Gas adsorption–desorption results are compared with the atomic force microscopy (AFM) data and solute retention ones for membranes with narrower pores. AFM is especially interesting as far as it is the best technique to analyze the surface roughness. It is worth noting that, among the methods leading to bulk porosity those detecting only thoroughly open pores give always more realistic estimations of the actual permeation performances.