Sorption Characteristics of Polymer Brushes in Equilibrium with Solvent Vapors

While polymer brushes in contact with liquids have been researched intensively, the characteristics of brushes in equilibrium with vapors have been largely unexplored, despite their relevance for many applications, including sensors and smart adhesives. Here, we use molecular dynamics simulations to show that solvent and polymer density distributions for brushes exposed to vapors are qualitatively different from those of brushes exposed to liquids. Polymer density profiles for vapor-solvated brushes decay more sharply than for liquid-solvated brushes. Moreover, adsorption layers of enhanced solvent density are formed at the brush-vapor interface. Interestingly and despite all of these effects, we find that solvent sorption in the brush is described rather well with a simple mean-field Flory-Huggins model that incorporates an entropic penalty for stretching of the brush polymers, provided that parameters such as the polymer-solvent interaction parameter, grafting density, and relative vapor pressure are varied individually.