MEMBRANE CHARACTERIZATION BY SOLUTE TRANSPORT AND ATOMIC-FORCE MICROSCOPY

Various ultrafiltration and nanofiltration membranes were characterize d by solute transport and also by atomic force microscope (AFM). The m olecular weight cut-off (MWCO) of the membranes studied were found to be between 3500 and 98,000 Daltons. The mean pore size (mu(p)) and the geometric standard deviation (sigma(p)) around mean ranged from 0.7 t o 11.12 nm and 1.68 to 3.31, respectively, when calculated from the so lute transport data. Mean pore sizes measured by AFM were about 3.5 ti mes larger than calculated from the solute transport. Pore sizes measu red by AFM were remarkably fitted to the lognormal probability distrib ution curve. Pore sizes of the membranes with low MWCO (20,000 Daltons and lower) could not be measured by AFM because of indistinct pores. In most cases, the pore density ranged from 38 to 1291 pores/mu m(2). In general, the pore density was higher for the membrane having lower MWCO. Surface porosity was around 0.5-1.0% as measured from the solute transport and was 9.5-12.9% as obtained from AFM images. When membran es were coated with a thin layer of sulfonated polyphenylene oxide, me an pore sizes were reduced for all the membranes. Surface roughness wa s also reduced on coating. (C) 1998 Elsevier Science B.V.