Improvement of water and gas barrier properties of polycarbonate by the SiOx plasma treatment

Abstract

The purpose of this research paper was to improve the water and gas barrier properties of polycarbonate (PC) by the deposition of organosilicon thin films through radio-frequency plasma treatment. For optimization, different treatment parameters (namely, the discharge power, the deposition time, and the ratio q between O2 and hexamethyldisiloxane) were varied. The influence of the plasma coating of low thickness (30–308 nm) on the surface and structure properties of PC and on its thermal stability was analyzed. The resistance toward gases (N2, O2, CO2) and water was investigated through permeation measurements. The results have shown that increasing the ratio q from 5 to 12.5 allows obtaining a layer of more inorganic nature and a O/Si ratio close to 2 enhances the PC thermal stability. It has been found that the barrier properties of the treated PC film mainly depend on the morphology of the deposited coating, its homogeneity and the surface wettability. For instance, with q = 7.5 leading to the less hydrophilic and more homogeneous treated surface, the barrier effect significantly increased, as the obtained barrier improvement factor was ∼ 60 % for gases and 24 % for water.