Examination of wettability and surface energy in fluorodecyl POSS/polymer blends

Fluorodecyl Polyhedral Oligomeric SilSesquioxane (POSS) is a low surface energy material ([gamma]sv [approximate] 10 mN m-1) that has been used as a coating to prepare a variety of liquid repellent surfaces. There are several drawbacks to employing pure fluorodecyl POSS as a coating, including high cost, poor adherence to the underlying substrate, and a lack of optical transparency. One potential strategy for overcoming these shortcomings while retaining liquid repellency is to prepare composite coatings by judiciously blending polymers with fluorodecyl POSS. Here varying amounts of fluorodecyl POSS are blended with commercially available poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(butyl methacrylate) (PBMA), and the commercial fluoroelastomer Tecnoflon BR9151. A film of each blend is spin cast onto a silicon wafer and its surface wettability is probed by measuring advancing and receding contact angles of six liquids: water, ethylene glycol, dimethyl sulfoxide, diiodomethane, rapeseed oil, and hexadecane. Surface energy analysis techniques developed by Girifalco, Good, and colleagues are used to extract the hydrogen bond donating (acidic), hydrogen bond accepting (basic), and nonpolar (dispersion) components of the solid surface energy from both advancing and receding contact angle measurements. It is emphasized that a proper assessment of the wetting behavior of a liquid on a surface requires consideration of the complementary acid-base interactions between the solid and the liquid, not just a determination of the polar contribution to the solid surface energy. Maximum liquid repellency is attained in composite PMMA or PEMA films with fluorodecyl POSS loadings of at least 20 wt %. Furthermore, cross-cut adhesion tests reveal that the optically transparent methacrylate-containing fluorodecyl POSS coatings adhere quite strongly to the underlying substrate, unlike the Tecnoflon-containing blends and the pure fluorodecyl POSS. These results will potentially facilitate the incorporation of fluorodecyl POSS into commercial coatings.