University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, 2000 Maribor, Slovenia
R. Šoster, M. Brumen, V. Ribitsch, D. Wiegel, K. Arnold and Č. Stropnik
University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000 Maribor, Slovenia
University of Maribor, Faculty of Education, Koroška 160, Maribor, Slovenia
Josef Stefan Institute, Jamova 39, Ljubljana, Slovenia
Karl-Franzens University, Institute of Physical Chemistry, Heinrichstrasse 28, A-8010 Graz, Austria
University Leipzig, Institute of Medical Physics and Biophysics, Leibigstrasse 27, D-04103 Leipzig , Germany
Asymmetric porous membranes were prepared from polysulfone by a wet-phase separation procedure. Different chemical modifications were applied to the upper membrane surface, i.e. the surface which was exposed to interaction with nonsolvent (water) in the coagulation bath during the membrane formation. The membrane surface was modified by the series of Friedel-Crafts electrophilic substitutions of aromatic rings in the polysulfone molecules. As a reagent 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 membranes, 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 the membrane surface affect the water flux, the zeta potential and contact angle values whereas the membrane thickness remains unchanged. These effects are interpreted in terms of hydrophilicity and hydrophobicity, changes of the 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 groups and reaction with propylene oxide gave a hydrophilic surface with polar group –CH(CH3)-CH2-OH. The surface of sulfonized polysulfone membranes contained ionizable (- SO3H) functional groups.