Systematic and Simulation-Free Coarse Graining of Diblock Copolymer Melts

Since full atomistic simulations of many-chain systems used in experiments are currently not feasible due to their formidable computational requirements, developing coarse-grained (CG) models (potentials) to greatly speed-up molecular simulations of real polymeric systems has attracted great interest. We recently proposed a systematic and simulation-free strategy for coarse graining multi-component polymeric systems [Q. Wang, Polymer 117, 315 (2017)], where we use the well-developed Polymer Reference Interaction Site Model (PRISM) theory, instead of the commonly used many-chain molecular simulations, for both the original and CG systems. Here we apply our strategy to the structure-based coarse graining of diblock copolymer melts, and examine in detail how the CG potentials vary with the coarse-graining level. We show analytically that our structure-based coarse-graining strategy does not change the order-disorder transition of symmetric diblock copolymer melts at the mean-field level. We also show, with highly accurate numerical results, that the CG system cannot reproduce the thermodynamic properties (i.e., the interchain internal energy per chain and virial pressure) of the original system at any coarse-graining level.