Gas permeation through rubbery polymer nano-corrugated membranes

The purpose of this investigation is to fabricate PDMS membranes with reliable surface roughness in order to reduce the surface resistances and to study its impact on the permeation rate. The permeance of CO₂ through PDMS membranes with rough surfaces at nanoscale is studied and compared with the one of membranes with flat surfaces. At very low thickness, rough membranes have a permeance greater than that of membranes with flat surfaces. The enhancement occurs in a regime where the gas transport is sorption desorption surface rate limited, and cannot be explained by the increase in surface area due to the corrugation. The analysis, introducing a phenomenological model in analogy with electrical flow, indicates that nano-corrugation reduces the surface resistance. To test the model, the permeance of N₂ is also measured in the same experimental conditions and the influence of surface roughness on permeation rate of CO₂, He, CH₄ and N₂ is studied. The comparison among the gases suggests that the Henry's coefficient depends on the surface roughness and allows discussing the role of roughness on membrane selectivity.