A novel prewetting behavior of water adsorbed on solid surfaces modified with tethered chains resulting from a density functional theory

Abstract

The density functional approach for classical associating fluids is used to explore wetting phase diagrams for model systems consisting of water and graphite-like solid surfaces chemically modified by a small amount of grafted chain molecules. The water-like fluid model is adopted from the work of Clark et al. [Molec. Phys. 104, 3561 (2006)]. It describes the bulk water vapor–liquid coexistence very well. Each chain molecule consists of tangentially bonded hard spheres. We focus on the investigation of the growth of water film on such a complex substrate and the construction of the wetting phase diagram. We have found that the topology of the phase diagram depends on the amount of grafted chains and on the length of chains. At low grafting densities and for short chains, the prewetting phase diagrams are similar to the diagrams for water on a non-modified solid surface. For higher grafting densities and for longer chains, the prewetting line can split into two lines that join at a triple point. Each of the lines is associated with changes in the predominant configuration of segments of grafted chains. They can either stretch or coil upon the growth of an adsorbed film. Trends of the behavior of wetting temperature and the critical temperatures of the branches of the prewetting transition are discussed.