Use of an electric field to alter membrane morphology in a polysulfone-polyvinylpyrrolidone blend

Abstract

An inherent characteristic of many polymer-based systems used in membrane manufacture is the tendency to form numerous defects such as macrovoids and pinholes. Such defects are manifested as large scale surface pores. In this research note we discuss the potential use of electric fields to influence the mechanisms by which these defects are formed during the precipitation step in the wet-cast phase-inversion process for polymeric membrane formation. Several electrical field phenomena including surface-induced-polarization, electrohydrodynamic convection, and enhanced transport can potentially be used to alter polymeric membrane morphology if the time scale for these electric field effects is short enough. We report preliminary experimental results corresponding to the formation of tubular membranes from a polysulfone-polyvinylpyrrolidone blend in a N,N-dimethylacetamide solution precipitated in water under the influence of an a.c. electric field. This study suggests that the electric field effects can be operative on the short time scale of membrane formation. Based upon the statistically significant differences in the frequency distribution of defect number versus defect area which were obtained, the results indicate that the presence of a 2.2 kV/cm a.c. electric field decreases the average number density of defects while increasing the total defect area. These results suggest that further experiments with more sophisticated equipment would permit the electric field effects to be optimized in order to reduce the number and the size of the surface defects.