Effects of supercritical carbon dioxide treatment conditions on the gas separation properties of polydimethylsiloxane hybrid membrane materials for air purification

Abstract

A siloxane/polydimethylsiloxane (PDMS) hybrid membrane containing fluorinated side chains was prepared by a convenient and mild sol-gel process and a crosslinking reaction. The effects of the supercritical carbon dioxide (scCO 2 ) conditions (i.e., treatment temperature, treatment time, and treatment pressure) on the permeation properties of fluorinated PDMS containing hybrid membrane were investigated. The chemical structure, microstructure, and physical performance of the membranes treated before and after were also discussed. The chemical structure of the PDMS membranes did not change with the scCO 2 treatment conditions. The membranes still retained better membrane-forming abilities, higher permeability, and selectivity than normal PDMS membranes. Compared to those of the membrane with membrane formation after scCO 2 treatment, the oxygen permeability coefficient and oxygen/nitrogen separation factor of the membrane with scCO 2 treatment before membrane formation were higher and were up to 7.11 Â 10 À8 cm 3 (STP) cm/(cm 2 s cmHg) and 3.27, respectively. The permeation properties of the hybrid membrane were obviously higher than those of Robeson's upper bound. The high air-purification performance of the hybrid membrane may have been due to the introduction of fluorine atoms into PDMS membrane, and the increase in free volume resulted from the plasticizing function of the scCO 2 treatment.

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