Ordering polymer blend morphologies via solvent evaporation

We present computer simulations of the phase separation dynamics in thin films of polymer blend solutions subject to solvent evaporation. We find that phase separation initially occurs at the air-film interface, where the solvent concentration is at its lowest. As the solvent diffuses through the film, and evaporates from the surface, phase separation becomes energetically favourable progressively throughout the film. However, phase separation is now initiated and directed by regions closer to the air surface which have already undergone phase separation. This, in effect, produces an ordering front which propagates through the film and leaves an ordered lateral morphology in its wake. Through computer simulations not only can we directly view this process, for the first time, but we can also predict the optical properties of the thin film as the solvent evaporates