Gas permeation through composite membranes prepared by plasma polymerization of fluorocarbon compounds

Permeation of simple gases (He, H{dollar}sb2,{dollar} CO{dollar}sb2,{dollar} O{dollar}sb2,{dollar} N{dollar}sb2{dollar} and CH{dollar}sb4{dollar}) through composite membranes was studied. The composite membranes were prepared by the deposition of plasma polymers onto polymer substrates in a microwave discharge.; In this research, we have investigated gas permeation properties of plasma polymers and permeation resistances of the interfacial layer in the composite membrane. The directional dependence of permeation has been also examined.; Permselective plasma films were produced from aromatic fluorocarbon compounds with high fluorine content. The permeability coefficient of the plasma films deposited on Celgard decreased as the size of penetrant molecules increased. This behavior suggests that the permeability is controlled by the diffusion coefficient. The plasma films showed higher CO{dollar}sb2{dollar}/CH{dollar}sb4{dollar} selectivities than those of commonly used polymers, while O{dollar}sb2{dollar}/N{dollar}sb2{dollar} selectivities were similar or slightly lower than those of common polymers.; Interfacial resistances to permeation were estimated using a modified series resistance model for composite membranes with nonporous poly(dimethlysiloxane) (PDMS) substrates. There was a significant interfacial resistance to CH{dollar}sb4{dollar} gas, which has the largest molecular size, while the resistance decreased as the size of penetrant molecules decreased. The interfacial resistance appears to be caused by the interfacial layer due to interactions and chemical bondings between PDMS and the plasma coating layer.; Gas permeation through composite membranes with nonporous PDMS substrates was affected by the direction of flow for CH{dollar}sb4{dollar} gas. The total permeation rate of CH{dollar}sb4{dollar} was 12 to 16% higher when the PDMS side was exposed to the high pressure than when the plasma coating layer side was exposed to the high pressure. The pressure dependence of the permeability coefficients of the plasma coating layer and interfacial layer seems to be responsible for the flow reversal effect. For N{dollar}sb2,{dollar} O{dollar}sb2{dollar} and CO{dollar}sb2,{dollar} the directional dependence of permeation was not observed.