Plasma polymer thin film depositions to regulate gas permeability through nanoporous track etched membranes

Deposition of thin polymeric films on nanoporous membranes is shown to provide a mechanically simple and inexpensive approach to regulate trans-membrane gas flows. For this purpose, polymeric films were deposited on polycarbonate track-etched (PCTE) membranes of 50 nm and 100 nm pore size. The films were generated by low-pressure glow discharge plasma polymerization of vinyl acetic acid (CH₂{double bond, long}CHCH₂COOH) or perfluorohexane (n-C₆F₁₄) monomers. The plasma discharge was operated under pulsed conditions to provide better control of the polymeric film chemistry along with improved control of film thickness. The gradual reduction in average membrane pore sizes with increasing film thickness resulted in controlled decreases in the permeation rates of O₂ and CO₂ gases. In addition to film thickness, the permeation rates were observed to be functions of the specific composition and cross-link density of the polymer films deposited, as well as the nature of the permeant gases. It was determined that the plasma deposition process employed provides sufficient permeation control for use in applications requiring fine modulation of gas permeation rate such as those encountered in development of a blood oxygenator, a major motivation for the present study.