Organic Surface Modifications on Silicone Elastomers: Impact on Moisture Vapor Permeability and Surface Energy Dynamics

The purpose of this study was to observe the effects of organic surface modifications on silicone elastomers with respect to moisture vapor permeability properties as a function of both grafted moiety functionality and packing density. We utilized chemical vapor deposition and mechanical manipulation of the elastomer to deposit (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane and 3-aminopropyltrimethoxysilane. As expected, the chemical vapor deposition of both species altered the chemistry of the elastomer surface to more hydrophobic for the fluorinated silane and more hydrophilic for the amino - terminated silane in the absence of mechanical elongation during the modification. As previously demonstrated, increasing the packing density of the silanes by increasing the degree of tension on the substrate during activiation and deposition, resulted in an increase in the contact angle of water. This turned out to be true even for the hydrophilic species. In all modified samples, the moisture vapor permeability (MVP) decreased by about 50% and is attributed to the ultraviolet/ ozone activation step that created a silica-like layer. Despite the reduction in MVP, the modified elastomer films are still considered to have a high moisture vapor permeability on the order of 5·10-1 g·mm/m2·hr·kPa.