Chemical modification and characterization of the surface of polysulfone membranes

Asymmetric porous membranes were prepared from polysulfone by a wet-phase s eparation procedure. Different chemical modifications were applied to the u pper membrane surface, i.e. the surface which was exposed to interaction wi th nonsolvent (water) in the coagulation bath during the membrane formation . The membrane surface was modified by the series of Friedel-Crafts electro philic substitutions of aromatic rings in the polysulfone molecules. As a r eagent 1-chlorodecane or propylene oxide dissolved in hexane and AlCl3 as a catalyst were used. In the former case a hydrophobic and in the latter one a hydrophilic coating was achieved, respectively. The membrane surface was also modified by sulfonization with sulfuric (VI) acid water solution; in this way negative charges were introduced at the membrane surface. The memb ranes, unmodified and chemically modified, were characterized by measuring the membrane thickness, the deionized water flux through the membrane, the zeta potential and contact angle. The specific chemical modifications of th e membrane surface affect the water flux, the zeta potential and contact an gle values whereas the membrane thickness remains unchanged. These effects are interpreted in terms of hydrophilicity and hydrophobicity, changes of t he membrane surface charge and the thickness of shear layer at the membrane surface, all with respect to the particular modification applied. Reaction with 1-chlorodecane gave a hydrophobic surface by nonpolar -(CH2)(9)-CH3 g roups and reaction with propylene oxide gave a hydrophilic surface with pol ar group -CH(CH3)-CH2-OH. The surface of sulfonized polysulfone membranes c ontained ionizable (- SO3H) functional groups.