Improved Moisture Barrier Properties of High Temperature Vulcanized Silicone Rubber by Direct Fluorination

Abstract

Our previous results have shown that surface hydrophobicity of a high temperature vulcanized silicone rubber can be significantly enhanced by direct fluorination. In this report, the surface fluorinated sample together with the virgin sample as a reference have been investigated on their water vapor barrier properties at $30^{\circ}C$ or $60^{\circ}C$ in a humidity environment of 75% or 97% RH. The experimental results show that the fluorinated surface layer has a high barrier to water vapor ingress into the interior of the SIR, so that the surface fluorinated sample has a much lower absorption of moisture in comparison with the virgin sample under the same conditions. SEM images show that the fluorination leads to the formation of a fluorinated surface layer with a thickness of 0.56 $\mu m$ and a nanostructured surface. The improvement of the barrier properties is attributed to a decrease in free volume of the surface layer as well as the increase in surface hydrophobicity by the fluorination, as indicated by contact angle measurements and ATR-IR and XPS analyses.