The polymeric membranes technology is a dynamic growing field, exploited in several areas of application like gas separation,[1] sensors, and vacuum technology.[2]It is based on well-known selective permeation process of gas through a polymer, whose selectivity for two different gas is the ratio of their permeability coefficients P. In the last years have been developed methods to fabricate ultra-thin membrane,[3] but there’s no estimation of P. Moreover, even if for thick membrane there is some results, the dependence of P from the thickness is generally poorly investigated. Here we present a novel method to fabricate stable and resistant ultra thin PDMS membranes, and we show their gas permeation characteristics as function of the membrane thickness and the type of gas: CO2 and He. The membranes have been fabricated by spin coating with thickness in the range between few micron and 500 nm. Afterwards, in order to guarantee the necessary mechanical stability, they have been transferred on SiN membrane previously drilled by focused ion beam with a number of apertures such that to have an appropriate permeation area (Fig. 1). Permeability measurements have been performed in high vacuum chamber, where the membranes have been exposed to 105 Pa of pressure differential without rupturing or stretching, proving their high strenght. The results confirm the higher permeability of the carbon dioxide respect to those of helium, whereas the value of P decreases unexpectedly with the membrane thickness, on the contrary of the CO2/He selectivity that remains constant. Studies on thickness-dependence of the gas permeability are scarce, but our data (Fig. 2) are in good agreement with a model that considers non-equilibrium reactions at gas-membrane interface. This make it possible the evalutation of the adsorption and desorption rates, and in conjuction with mechanical properties of the membranes, suggests new technological solutions in the devices miniaturization.
Fabrication and gas permeation properties of ultra-thin PolyDiMethylSiloxane (PDMS) membranes
FIRPO, GIUSEPPE;E. Angeli;REPETTO, LUCA;IERARDI, VINCENZO;F. Buatier de Mongeot;VALBUSA, UGO
2013-01-01
Abstract
The polymeric membranes technology is a dynamic growing field, exploited in several areas of application like gas separation,[1] sensors, and vacuum technology.[2]It is based on well-known selective permeation process of gas through a polymer, whose selectivity for two different gas is the ratio of their permeability coefficients P. In the last years have been developed methods to fabricate ultra-thin membrane,[3] but there’s no estimation of P. Moreover, even if for thick membrane there is some results, the dependence of P from the thickness is generally poorly investigated. Here we present a novel method to fabricate stable and resistant ultra thin PDMS membranes, and we show their gas permeation characteristics as function of the membrane thickness and the type of gas: CO2 and He. The membranes have been fabricated by spin coating with thickness in the range between few micron and 500 nm. Afterwards, in order to guarantee the necessary mechanical stability, they have been transferred on SiN membrane previously drilled by focused ion beam with a number of apertures such that to have an appropriate permeation area (Fig. 1). Permeability measurements have been performed in high vacuum chamber, where the membranes have been exposed to 105 Pa of pressure differential without rupturing or stretching, proving their high strenght. The results confirm the higher permeability of the carbon dioxide respect to those of helium, whereas the value of P decreases unexpectedly with the membrane thickness, on the contrary of the CO2/He selectivity that remains constant. Studies on thickness-dependence of the gas permeability are scarce, but our data (Fig. 2) are in good agreement with a model that considers non-equilibrium reactions at gas-membrane interface. This make it possible the evalutation of the adsorption and desorption rates, and in conjuction with mechanical properties of the membranes, suggests new technological solutions in the devices miniaturization.
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