Gas permeation properties of selected pulsed-plasma polymers.

摘要

Gas separation membranes were prepared from three different monomers by pulsed plasma deposition. The first monomer was hexamethyldisiloxane. It is found to form solution-diffusion type membranes when deposited on top of a high permeability, low separation commercial dimethylsiloxane membrane. Pulsed, intermediate power—5 ms on, 5 ms off, 150 W peak—was found to produce the best and most reproducible membranes. The separation factor of the dimethylsiloxane membrane for the carbon dioxide/methane pair is improved from 3.2 to 5.7 with an 8,000 Å thick film deposited under these condition. An excellent correlation between the plasma power used, the thickness of the film deposited and the permeance of the membrane was found.; The second type of membrane produced was from the pulsed plasma deposition of poly(allyl alcohol). It was found that only low duty cycle, pulsed plasma deposition (1 ms on/30 ms off, 300 W peak power) produced membranes of sufficient density to permit permeation measurement. The membranes were deposited on porous ceramic filters, and were found to permeate common gases though a combination of porous flow and the flow of adsorbed gases on the inner surface of the pores. The degree of surface transport was correlated with the critical temperature of the gas under test. The amount of surface transport for all gases tested increased strongly with applied pressure. The poly(allyl alcohol) films were compared with published data for porous cellulose acetate membranes; it was found that the poly(allyl alcohol) membranes had greatly enhanced surface transport compared to the cellulose acetate membranes.; Poly(pentaflurostyrene) membranes were deposited on ceramic filters from a pulsed duty cycle plasma (1 ms on/10 ms off, 50 W peak). These membranes were also found to be porous; however, virtually no surface transport of gases was observed.; The degree of surface transport in the two plasma membranes produced, and in the cellulose acetate membrane data suggest that surface transport is enhanced in high surface energy porous materials, and retarded in low surface energy materials.