Dissipative Particle Dynamics Study for the Phase Separated Structures of Polymer Thin Film Caused by Solvent Evaporation

We study the evaporation process which causes phase separation using the dissipative particle dynamics. To simulate the evaporation, we modify the method introduced by Yamamoto et al: we exchange the solvent particle with the gas particle not in the region near the surface, but in the region far from the surface. This method allows us to control the evaporation rate, and to analyze the solvent distribution in the gas phase. For the evaporation of the polymer solution of binary polymer blend, we found two types of structure in the dried film, one is that phase separated domains is orthogonal to the film, and the other parallel to the film. We found that in addition to the difference in the interaction between polymer and substrate, and that between polymer and gas, the interaction between polymer and solvent can cause such structural change.