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

A thin SiOx surface layer was formed on porous Nylon(R) membranes coated wi th a cross-linked polysiloxane by exposure to ultraviolet light at room tem perature in the presence of atmospheric oxygen. The transformation of the c ross-linked polysiloxane to SiOx was monitored by X-ray photoelectron spect roscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), contact angle analysis and atomic force microscopy (AFM). A continuous sur face layer of SiOx formed after about 1 h of UV exposure. AFM analysis reve aled that a nodular structure with a characteristic size less than 0.5 nm f ormed after extended UV exposure. Gas permeation measurements on the compos ite membranes documented interesting gas separation properties: the CO2 per meance of the cross-linked polysiloxane/Nylon(R) composite membrane before irradiation was 8.9x10(-8) mol m(-2) s(-1) Pa-1, and the CO2/N-2 selectivit y was 22; after UV-ozone induced formation of the SiOx surface layer, the p ermeance decreased to 5.1x10(-8) mol m(-2) s(-1) Pa-1 while the selectivity for CO2/N-2 increased to 48. (C) 2000 Published by Elsevier Science B.V.