Preparation of bifunctional poly(dimethylsiloxane) membrane by dual X-linking

Abstract

A new class of poly(dimethylsiloxane) (PDMS) membranes with increased hydrophobicity, in which hydroxyl terminated poly(dimethylsiloxane) HPDMS macromolecules are cross (X)-linked concurrently with polymethylhydrosiloxane (PMHS) macromolecules and n-octadecyltrichlorosilane (OTS) molecules, is reported here. The unique bifunctional PDMS membranes possess improved membrane performance for removal of trace volatile organics from water, thereby showing high potential for treatment of organic polluted water, considering zero discharge and stringent norms for disposal of industrial effluents. Series of the membranes with fixed HPDMS and PMHS ratios but different OTS content varying from 0.1 to 20 wt% were prepared. This resulted in formation of two different types of bifunctional PDMS membranes. The membranes with lower OTS content (<5 wt%) resulted in formation of homogeneous structures in which OTS is X-linked molecularly, whereas nanocomposite structures with the additional presence of very small organosilica particles of about 1–2 nm size, were observed in the membrane with 5 wt% OTS loading. In membranes with excess 10–20 wt% OTS loading, these nanoparticles were aggregated. The nanoscale structure observed by TEM was in accord with the SANS profiles. The membranes were further characterized by SEM, NMR, IR, contact angle, swelling and X-linking density measurements and correlated with their separation performances. The membrane with OTS content of 1 wt% exhibited the best performance in terms of high permselectivity of benzene or dichloromethane over water.