Systematic coarse-graining of a polymer blend: Polyisoprene and polystyrene

The Iterative Boltzmann Inversion technique ( also known as the Inverse Boltzmann Method) is generalized to polymer blends. We systematically optimize a mesoscale model against the structure of the blend. A polyisoprene-polystyrene blend is used as an example. Atomistic simulations of a blend of short chains in the miscible regime under melt conditions are taken as a starting point. We optimize the mesoscale model and study the onset of phase separation with increasing chain length. The mesoscale model phase separates at a chain length of 15 monomers where it was optimized, whereas the atomistic model shows only a preference of chains to aggregate to neighborhoods of like chains. We discuss the differences of the optimization between a blend and a homopolymer system in detail.