Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon Dioxide

Abstract

The thickness and refractive index of poly(dimethylsiloxane) (PDMS) thin films on silicon, exposed to high-pressure carbon dioxide, have been measured in-situ by spectroscopic ellipsometry. The swelling of the film is determined from the thickness and the sorption of CO2 from the refractive index. The sorption and swelling values for the thin films exceed those of the bulk films. These increases may be attributed to excess CO2 at the polymer thin film−CO2 and polymer−silica interfaces and the influence of the silica surface and CO2 on the orientation of the polymer. Pressure-induced birefringence of the fused-silica windows was addressed in the model calculations and corrections were found to be successful for a thermal oxide reference wafer and the PDMS films. Large surface excesses of CO2 on the reference wafer were observed in regions where CO2 is highly compressible due to critical adsorption.

Pore Expansion in Mesoporous Silicas Using Supercritical Carbon Dioxide

“…Thus, properties such as surface area and pore diameters of porous polymers can be manipulated through CO 2 pressure changes. Johnston and co-workers 32 have also used CO 2 to swell thin films of poly(dimethylsiloxane) on silicon substrates. Film swelling was measured using in situ high pressure elliposmetry techniques.…”

Membrane technologies for CO2 capture

“…Aboudheir et al [33] determined the absorption rate for partial loaded MEA solutions for three different degrees of CO 2 loading (0.0996, 0.3015, 0.4725 mol/mol) and also observed a strong decrease with increasing CO 2 loading degree.…”

“…The densities of the gas and the polymer and the refractive index of pure CO 2 can be obtained from literature [33], whereas the refractive index of the pure polymer can be experimentally determined from an ellipsometry experiment at zero pressure (vacuum).…”

“…It is the most often industrially used solvent for the chemical absorption of CO 2 . The amine groups present in the solvent selectively and reversibly react with the CO 2 from the feed, a mechanism that has been studied frequently [32][33][34]. We investigate the effect of the liquid flow rate, feed pressure and temperature of absorption and desorption for the two chosen membrane types.…”

“…This make them a viable technology for gas-liquid contacting processes such as the separation of olefins and paraffins [27,31,32], blood oxygenation [33] and the separation of CO 2 from light gases [25].…”