Ss. Shojaie et al., USE OF AN ELECTRIC-FIELD TO ALTER MEMBRANE MORPHOLOGY IN A POLYSULFONE POLYVINYLPYRROLIDONE BLEND, Journal of membrane science, 79(1), 1993, pp. 115-122
An inherent characteristic of many polymer-based systems used in membr
ane manufacture is the tendency to form numerous defects such as macro
voids 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 i
ncluding surface-induced-polarization, electrohydrodynamic convection,
and enhanced transport can potentially be used to alter polymeric mem
brane morphology if the time scale for these electric field effects is
short enough. We report preliminary experimental results correspondin
g to the formation of tubular membranes from a polysulfone-polyvinylpy
rrolidone blend in a N,N-dimethylacetamide solution precipitated in wa
ter under the influence of an a.c. electric field. This study suggests
that the electric field effects can be operative on the short time sc
ale of membrane formation. Based upon the statistically significant di
fferences 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 perm
it the electric field effects to be optimized in order to reduce the n
umber and the size of the surface defects.