UV–ozone induced growth of a SiO x surface layer on a cross-linked polysiloxane film: characterization and gas separation properties

Abstract

A thin SiO x surface layer was formed on porous Nylon ® membranes coated with a cross-linked polysiloxane by exposure to ultraviolet light at room temperature in the presence of atmospheric oxygen. The transformation of the cross-linked polysiloxane to SiO x was monitored by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), contact angle analysis and atomic force microscopy (AFM). A continuous surface layer of SiO x formed after about 1 h of UV exposure. AFM analysis revealed that a nodular structure with a characteristic size less than 0.5 nm formed after extended UV exposure. Gas permeation measurements on the composite membranes documented interesting gas separation properties: the CO 2 permeance of the cross-linked polysiloxane/Nylon ® composite membrane before irradiation was 8.9×10 −8 mol m −2 s −1 Pa −1, and the CO 2/N 2 selectivity was 22; after UV–ozone induced formation of the SiO x surface layer, the permeance decreased to 5.1×10 −8 mol m −2 s −1 Pa −1 while the selectivity for CO 2/N 2 increased to 48.