Enhancement of Adhesion Strength of Perfluoroalkylpolyethers on Rough Glassy Silica for Antismudge Coatings

Abstract

The adhesion behavior of perfluoropolyether (PFPE) on rough silica surfaces is investigated by steered molecular dynamics simulations. To reproduce bond breakage during sliding of PFPE, a dynamic bond breaking method is developed and applied to the PFPE-silica interface. Calculated results reveal that nanoscale roughness is a critical parameter that affects the adhesion strength due to the PFPE film thickness of 1 nm, and the adhesion strength also depends on the molecular density of PFPE on the silica surface. The effect of roughness amplitude, spacing, and molecular weight of PFPE are individually analyzed to find a key parameter for adhesion enhancement. Adhesion strength on a flat surface is highest and decreases with increasing roughness within the considered conditions. When R-a = 17.5 angstrom adhesion strength is 3 times lower than the flat surface, and vacant pores at the interface are observed, which implies a reduced molecular density of PFPE from 0.31 to 0.27 molecules/nm(2). Increasing the roughness spacing removes vacant pores at the interface and hence, adhesion enhances up to 50% of the original interface. Decreased molecular weight is another way to increase surface density of PFPE, and the highest adhesion is observed with the lowest molecular weight of PFPE. Comparing the change of adhesion strength, both roughness amplitude and molecular weight are determined as key parameters for enhancing adhesion strength.