Nanodroplets of Polymer Solutions on Solid Surfaces: Equilibrium Structures and Solvent Evaporation

We propose computer simulations revealing the internal structure of liquid droplets formed by polymer solutions. Both suspended and droplets placed on a solid surface are simulated. In the case of droplets, which are in equilibrium with the solvent vapor (nonvolatile droplets), distribution of polymer chains is studied versus thermodynamic quality of the solvent (good and bad) and interactions of the polymer and the solvent with the surface. Both swollen and collapsed states of the chains within the droplet, their localization at the liquid–vapor interface, and adsorption on the solid surface are predicted. We construct various diagrams of states of the droplets. Then, we simulate a fast solvent evaporation from the droplet placed on a solid surface and study nonequilibrium polymer structures. The conditions for the appearance of a coffee ring (a ring-wise distribution of polymer after solvent evaporation) and homogeneous polymer layer are predicted.