| In this work, the permeation of gases and condensible vapors through composite membranes was studied. Helium, hydrogen, argon, oxygen, nitrogen, methane, carbon dioxide, ethylene, acetylene, sulfur dioxide, propane, n-butane and sulfur hexafluoride were used as permeant gases.; Composite membranes were prepared by the deposition of either radio-frequency or microwave plasma polymerized siloxanes onto polymer substrates of porous Celgard. The starting monomer was either hexamethy1disiloxane (HMDSO) or octamethyl-cyclotetrasiloxane (OMCTSO).; The films were characterized by FTIR, ESCA, TGA, density and contact angle measurements. The permeabilities of the of the microwave and radio-frequency plasma polymerized siloxane membranes for thirteen gases were measured and compared.; The permeabilities were similar to those for conventional PDMS. Temperature and pressure dependence of permeability was measured. From the temperature dependence of permeability, activation energies for permeation were calculated. These were positive except for permeation of butane in RF PPHMDSO, which was negative. The activation energies were lower than for conventional PDMS. The permeabilities did not strongly depend on pressure up to 42 psia.; It was observed that permeabilities for gases showed dependence on molecular size, but the correlation was not as strong as for plasma polymerized fluorocarbon membranes. As molecular size increased from 2.58 A (helium) to 5.6 A (sulfur hexafluoride), the permeabilities of the membranes exhibited a decreasing trend. Within a group of permeant gases of similar size, e.g. argon, oxygen and nitrogen, or methane and carbon dioxide, the permeabilities increased with critical temperature. It was also observed that the solubility parameter, delta, correlated with the permeability for gases having similar molecular size.; The density of the films increased in the order: RF PPHMDSO < microwave PP HMDSO < microwave PP OMCTSO. Permeabilities decreased, and O2/N 2 selectivity increased, as the density of the plasma polymer films increased.; Permeation of butane through RF PPHMDSO showed unusual behavior. The permeation activation energy was negative. Butane permeation reduced the permeability of the membrane to nitrogen by 15%. After a 24 hour period the permeability returned to normal. |
