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.
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