Photoextraction of molecular gases from an organic polymer film

Abstract

Photoextraction of various molecular gases from a polydimethylsiloxane (PDMS) polymer film has been studied. Change in the density of molecular gases has been measured as a function of the illumination duration, intensity and wavelength of light, and temperature of the coating. A linear dependence of the rate of photoextraction on the intensity of the incident light has been established. Similar to the photoelectric effect, photoextraction is absent in the long-wavelength spectral range down to 550 nm. The effect increases sharply in the short-wavelength spectral range below a threshold of about 550 nm. Photoextraction is absent at temperatures below the glass-transition temperature of PDMS (−125°C), at which, as is known, the bulk diffusion of molecular gases in the film is strongly suppressed. At long-term irradiation of the film, the number of photoextracted molecules decreases exponentially with time. This increase is accompanied by a long tail of a diffusion form. The results indicate that photoextraction has a nonthermal nature and demonstrate the important role of bulk diffusion in the process of light-induced extraction of molecules from the surface.