Pore Size Distributions in Microporous Membranes: I. Surface Study of Track-Etched Filters by Image Analysis

Abstract

The surface morphology of several Cyclopore filters, consisting of thin track-etched sheets of polycarbonate, is analyzed here. Scanning electron microscopy and computerized image analysis have been applied. The surface porosity and the pore density or number of pores per surface unit are directly obtained for each filter, while the statistical distribution of the pore areas, pore perimeters, equivalent pore diameters, and pore shape factors are studied as well. These pore size distributions have been studied for six types of filters (C01, C02, C04, C06, C08, and C10) and the existence of a relevant portion of double and other multiple pores has been revealed. The fraction of these multiple pores are correlated with the nominal pore radii. The results on pore size have been used to predict the volume flows of the membranes studied. This can be done only by assuming that the surface characteristics remain unchanged in the internal volume of the filters, which leads to hydrodynamic radii well in accordance with the experimental ones, within the error range. Nevertheless, it seems that some of the pores should have internal widenings with inner radii close to 120% of the external ones.