Incorporation of fluorinated surfactants into polysulfone films and asymmetric gas separation membranes

Abstract

This study investigated the effect of incorporating strong surfactants into hollow fiber membranes and solution cast films made from polysulfone (PSF). During membrane formation, various (mostly fluorinated) surfactants were added to the spinning solution, quench medium, and bore fluid. Both the gas transport properties and the membrane structure were affected. Some membranes showed a modest increase in selectivity or in permeation rate. At low concentrations the addition of perfluoro ammonium octanoate (PAO) increased the O2 permeation rate by 44% with only a small loss of selectivity. Surfactants were also incorporated into dense PSF films by solution casting. Only pure PSF films and those with low concentrations of short-tailed fluorinated surfactants were clear and transparent; higher concentrations and other surfactants yielded cloudy or defective films. The presence of surfactants decreased the glass transition temperature of PSF to varying extents. Increased total and polar surface free energy correlated with changes in the gas transport properties. It is proposed that the surfactants interact with the polymer both during membrane and film formation, and also affect chain packing after the solvent has been removed. SEM images confirmed that membranes with surfactants have larger voids in the porous matrix of the membrane. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 163–175, 1999