XPS characterization of poly(methylhydrosiloxane)-modified cellulose diacetate membranes

The surface composition of a series of poly(methylhydrosiloxane) (PMHS)-modified cellulose diacetate (CDA) membranes was examined by X-ray photoelectron spectroscopy (XPS). The Si2p signal is a unique diagnostic feature for PMHS, thus allowing a straightforward determination of the relative proportion of this modifier on the surface of CDA. The surface compositions of the membranes under test reach readily a steady composition as a result of various treatments (initial PMHS concentration, solvent volume and reaction time). This parallels the performance of the membranes for reverse osmosis desalination. Chlorides were detected in the untreated CDA and the modified membrane for which salt rejection was poor. The Si2p binding energy indicates possible covalent grafting of the PMHS to CDA via an Si–O–C linkage.