The Influence of Low-Temperature Plasma on the Structure of Surface Layers and Gas-Separating Properties of Polyvinyltrimethylsilane Membranes

Abstract

New results of one-sided surface modification of polymeric films and composite membranes of polyvinyltrimethylsilane (PVTMS) using low-temperature plasma are presented. The treatment was carried out by direct current discharge at the cathode and anode, air was used as the working gas, the exposure time was from 10 to 60 s, and the working pressure in the chamber was 15–20 Pa. The structure of the surface layers was analyzed by XPS, AFM and SEM, and the contact properties of the surface were also studied. The effective permeability coefficients for O2, N2, CH4, CO2, He, and H2, as well as for gas diffusion, for cathode-treated PVTMS films are experimentally obtained, and the effective gas solubility coefficients are calculated. The permeability coefficients of the studied gases for composite membranes with a selective PVTMS layer modified at the cathode and anode were determined. It has been noted that the choice of electrode significantly affects not only the chemical structure of the surface and near-surface layers of PVTMS, but also the gas transport parameters of the modified samples. At the same time, during the treatment of PVTMS films at the cathode for 30 s, it was possible to achieve an increase in the O2/N2 selectivity by more than two times relative to the initial value. It has been established that the results of modification of composite membranes differ from those obtained for homogeneous films and it was possible to achieve O2/N2 selectivity in 2.5 times higher than the initial value. The potential of using surface modification of polymer films and membranes by low-temperature plasma to improve their gas separation properties is shown.