Stratification in Drying Polymer-Polymer and Colloid-Polymer Mixtures

Drying polymer polymer and colloid polymer mixtures were studied using Langevin dynamics computer simulations. Polymer polymer mixtures vertically stratified into layers, with the shorter polymers enriched near the drying interface and the longer polymers pushed down toward the substrate. Colloid polymer mixtures stratified into a polymer-on-top structure when the polymer radius of gyration was comparable to or smaller than the colloid diameter, and a colloid-on-top structure otherwise. We also developed a theoretical model for the drying mixtures based on dynamical density functional theory, which gave excellent quantitative agreement with the simulations for the polymer polymer mixtures and qualitatively predicted the observed polymer-on-top or colloid-on-top structures for the colloid polymer mixtures.