CHEMICAL AND ELECTRICAL CHARACTERIZATION OF VIRGIN AND PROTEIN-FOULEDPOLYCARBONATE TRACK-ETCHED MEMBRANES BY FTIR AND STREAMING-POTENTIAL MEASUREMENTS

Electrical properties for a range of virgin and protein-fouled polycar bonate track-etched (PCTE) membranes have been determined by streaming -potential measurements at pH 4-7 and 10(-3) M KCl at 25 degrees C. Th e apparent zeta potentials generally increased with increasing pore si ze above pH 5 and decreased with pore size below pH 5, For membranes w ith smaller pores (PCTE 0.01, 0.03 and 0.05 mu m) the zeta potentials became constant (the surface is fully charged) at about -6 mV at pH gr eater than or equal to 5, whereas those of larger pores (PCTE 0.1 and 0.2 mu m) showed constant zeta potentials of ca. -10 to -13 mV at pH > 6. In contrast, the protein-fouled membranes showed very similar appa rent zeta potential vs. pH profiles for all pore sizes. This suggests that the measured zeta potentials are determined by the protein proper ties. The loss of strong pore-size dependence on zeta potentials upon protein fouling of membranes implies that membrane zeta potentials cou ld be controlled by the conditions at pore entry, This 'model' require s protein deposition around the pore openings for all pore sizes; this was in agreement with electron microscope observations. While the iso electric points (IEP) of the virgin membranes determined from the pH d ependence of streaming-potential measurements were between pH 3.7-4.4 with a trend to higher IEP for the larger pore membrane, all protein-f ouled membranes showed IEP values at pH 4.6-4.8, which is close to the IEP of the BSA protein used. The chemical properties of the PCTE memb ranes investigated had FTIR spectra similar to those of polycarbonate from bis(4-hydroxyphenyl)-2-propane, bisphenol A polycarbonate. No BSA peak was revealed in the FTIR spectra of the small-pore membranes fou led with protein, possibly due to the insufficient instrument detectio n limit. For the membranes with larger pores, however, the BSA peaks i ncreased with increasing pore size. The depth profiling of the fouled membranes indicated a predominant BSA adsorption on the surface or nea r the pore entries rather than throughout the membrane thickness, conf irming the zeta potential 'model' and electron microscope observations .