Adsorption characteristics of silane-functionalized perfluoropolyether on hydroxylated glassy silica surfaces: A multiscale approach

Abstract

The adsorption mechanism and the structural features of perfluoropolyether (PFPE)-containing layers from silane-functionalized derivate (SPFPE) on hydroxylated glassy silica surfaces are systematically investigated by utilizing density functional theory and molecular dynamics simulations. It is found that each individual SPFPE molecule tends to be chemisorbed on the silica surface by forming a single siloxane bond regardless of the number of reactive branches in the functional end group of the SPFPE molecules. We also reveal that the formation of multiple siloxane bonds between a single SPFPE molecule and the hydroxylated silica surfaces is hindered by not only the constraint on geometrical optimization of the absorbed molecule but also the preexisting hydrogen bonds between adjacent hydroxyl groups on the surfaces. With a structural analysis, the adsorption orientation of SPFPE molecules is predicted as parallel to the silica surface, which induces low surface coverage (similar to 0.31 molecules/nm(2)) and sub-nano thickness (similar to 8 A) of the absorbed PFPE-containing layer. These adsorption characteristics are distinct from those of self-assembled monolayers consisting of fluorocarbon or hydrocarbon molecules. We believe that the fundamental understanding of adsorption mechanism and molecular morphology of the PFPE-containing layers demonstrated in this study can contribute to developing new advanced anti-fouling materials with improved mechanical property.