Friends, Foes, and Favorites: Relative Interactions Determine How Polymer Brushes Absorb Vapors of Binary Solvents

Polymer brushes can absorb vapors from the surrounding atmosphere, which is relevant for many applications such as in sensing and separation technologies. In this article, we report on the absorption of binary mixtures of solvent vapors (A and B) with a thermodynamic mean-field model and with grand-canonical molecular dynamics simulations. Both methods show that the vapor with the strongest vapor-polymer interaction is favored and absorbs preferentially. In addition, the absorption of one vapor (A) influences the absorption of another (B). If the A-B interaction is stronger than the interaction between vapor B and the polymers, the presence of vapor A in the brush can aid the absorption of B: the vapors absorb collaboratively as friends. In contrast, if the A-polymer interaction is stronger than the B-polymer interaction and the brush has reached its maximum sorption capacity, the presence of A can reduce the absorption of B: the vapors absorb competitively as foes.