Preparation and oxygen/nitrogen permeability of PDMS crosslinked membrane and PDMS/tetraethoxysilicone hybrid membrane

Abstract

A crosslinking agent containing silicon–hydrogen bonds and trimethoxylsilicon groups was synthesized and characterized by controlling molar ratio of 2,4,6,8-tetramethylcyclotetrasiloxane and vinyltrimethoxysilane. The crosslinked membranes and the organic–inorganic hybrid membranes were also prepared by using the crosslinking agent, polydimethylsiloxane containing 10% vinyl group and tetraethoxysilicone as the matrix material. There were three types of the crosslinking reactions in membrane-forming process. They included an addition reaction between the silicon–hydrogen bond and the vinyl group, hydrolysis and condensation themselves and between trimethoxylsiloxane and TEOS, respectively. The chemical structure and morphology structure of the membranes were characterized by FTIR and SEM and the mechanical properties of the membranes were also measured. The hybrid membrane containing 25.0% TEOS showed better membrane-forming property and the best mechanical performance as well as oxygen/nitrogen permeability. Permselectivities of the hybrid membranes were measured to show better oxygen/nitrogen permeability. For example, at 30 °C and pressure difference of 0.05 MPa, oxygen permeability coefficient and ideal separation factor were 370 Barrer and 3.45, respectively. As the TEOS content in the membranes increased, oxygen permeability coefficient decreased gradually, but ideal separation factor for oxygen and nitrogen firstly increased and then decreased obviously. Compared with ordinary PDMS membrane, not only the modified method was simple, but also the oxygen/nitrogen permeability of the hybrid membrane was enhanced obviously. The oxygen/nitrogen permeability of the hybrid membrane was higher obviously than those of Robeson's upper bound.