Characterization of gas transport properties of poly(dimethylsiloxane)-modified membranes

Poly(dimethylsiloxane) (PDMS) is one of the most permeable polymers due to its high free volume and flexible nature. Substituent groups can be incorporated with PDMS, making it suitable for further modification. This research effort is aimed at developing the fundamental structure/property relations of three relatively novel PDMS-modified polymer membranes: UV-crosslinked PDMS-containing polyimide copolymers (PIS), PDMS/graphene oxide (GO) nanocomposites, and PDMS-coated reverse osmosis (RO) membranes. A series of newly synthesized PIS copolymer membranes and their corresponding UV-irradiated analogs are presented. This work examined the chemical structure of these polymers and the effect of UV irradiation on gas transport. PIS copolymers exhibited a phase-separated structure, comprising a dispersed PDMS phase and a continuous polyimide phase. Gas permeability increased and selectivity decreased with UV irradiation. In addition to UV-crosslinked PIS copolymers, the contribution of gas sorption and diffusion to permeation for PDMS/GO nanocomposites was investigated. With increasing GO content, solubility selectivity changed little, but diffusivity selectivity increased significantly, which explains the gas selectivity improvement observed for these nanocomposites. A possible configuration for the dispersed GO structure in the PDMS matrix is presented based on X-ray characterization. The results agree favorably with behavior tracked by diffusion analyses. The viability of using commercial RO membranes for gas separation applications was also studied. A modification technique used in this study is coating RO membranes with a thin layer of PDMS, which is designed to plug (i.e., caulk) or fill any small (e.g., nm or sub-nm) pores present in the membrane’s separation layer. The analysis of pure- and mixed-gas transport data allows for a determination of the potential of RO membranes for gas separation applicationsChemical Engineerin