X-ray action on polymeric membrane surfaces:: a chemical and morphological characterization

The surfaces of six polymeric membranes-two polysulphone membranes, two composite reverse-osmosis polyamide/polysulphone membranes having polyamide as the active layer and two activated membranes containing di-2-ethylhexylphosphoric acid and di-2-ethylhexyldithiophosphoric acid as carriers, respectively-have been characterized before and after irradiation with an x-ray source, both chemically and topographically by XPS and atomic force microscopy (AFM), respectively. Changes in atomic concentrations of the characteristic elements of the membranes and in the shape of XPS spectra as a function of irradiation time can be related to chemical modifications on the membrane surface. The most significant changes have been observed for polysulphone, which is reduced by x-ray action; this fact also shows the inhomogeneity of the surface of the di-2-ethylhexyldithiophosphoric-activated membrane. In contrast, polyamide top layers of composite membranes have been shown to be the most stable. Chemical modifications are not related directly to changes in membrane roughness because for all membranes only small changes have been observed for AFM images recorded before and after membrane irradiation. Moreover, the roughness of both polysulphone membranes decreases slightly due to x-ray radiation but increases slightly for all polyamide-containing membranes (composite and activated membranes). Copyright (C) 2003 John Wiley Sons, Ltd.