The effect of sodium dodecyl sulfate solutions as gelation media on the formation of PES membranes

Sodium dodecyl sulfate (SDS) aqueous solutions were used as gelation media in the preparation of polyethersulfone (PES) membranes. The casting solution composition was the same for all the tested membranes. The temperatures of gelation media were 4 and 20 degreesC. The concentration of SDS was changed from 0 to 3.0 g/l at 4 degreesC and 0 to 1.6 g/l at 20 degreesC. The surface tension of the gelation media was measured by drop weight method and the electrical conductivities were also determined. The membranes were characterized by transport parameters obtained from separation experiments and roughness parameters, obtained by the atomic force microscopic (AFM) technique. The molecular weight cut-off (MWCO) values bf the studied membranes were found to be between 9 000 and 88 000 Da for membranes gelled at 4 degreesC, and between 28 000 and 85 000 Da for membranes gelled at 20 degreesC. The pore sizes were found to be between 3.04 and 10.73 nm for the membranes gelled at 4 degreesC and between 4.48 and 10.74 nm for membranes gelled at 20 degreesC, respectively. In general, both MWCO and pore size decreased with an increase of SDS concentration in gelation media when the concentration was below critical micelle concentration (CMC) and increased with an increase with SDS concentration when the concentration was above CMC. Images of membrane surfaces, taken by AFM, showed that the size of nodules and depressions decreased with a decrease in pore size. The roughness of membranes increased with an increase in pore size and MWCO. (C) 2001 Elsevier Science B.V. All rights reserved.