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

Abstract

Sodium Dodecyl Sulfate (SDS) aqueous solutions have been used as gelation media in the preparation of polyethersulfone (PES) membranes. The casting solution composition was the same for all casted membranes. Two temperatures were applied to the gelation media: 4°C and 20°C. The concentration of the SDS was changed from 0 to 3.0 g/L at 4°C and from 0 to 1.6 g/L at 20°C. The surface tension of the gelation media was measured by the drop weight method and their electrical conductivities were measured by CDM 80 conductivity meter. The membranes were characterized by solute transport parameters obtained from separation experiments and roughness parameters obtained by the atomic force microscope technique (AFM). The molecular weight cut-off (MWCO) of the studied membranes was found between 9,000 and 88,000 Daltons for membranes gelled at 4°C, and between 28,000 and 85,000 Daltons for membranes gelled at 20°C. For both temperatures, the lowest MWCO was obtained for membranes gelled in gelation media with a surface tension slightly lower than the critical micelles concentration (CMC). The pore sizes were found to be between 3.04 and 10.37 nm for membranes gelled at 4°C and between 4.48 and 10.74 nm for membranes gelled at 20°C. The pore density ranged from 4.79 to 939 pores/mum2 for membranes gelled at 4°C and from 8.14 to 109.6 pores/mum2 for membranes gelled at 20°C. In general, MWCO and pore size decreased with an increase of SDS concentration in gelation media below CMC, and increased with an increase in SDS concentration in gelation media above CMC. Images of membranes surfaces, by AFM technique, showed that nodules and depressions decreased with a decrease in pore size. The roughness of membranes increased with an increase in pore size and MWCO.