(38f) Systematic and Simulation-Free Coarse Graining of Polymer Blends and Block Copolymers

We propose a systematic and simulation-free strategy for coarse graining multi-component polymeric systems (e.g., polymer solutions, blends, nanocomposites, etc.), where we use the well-developed polymer reference interaction site model theory, instead of many-chain molecular simulations, for both the original and CG systems, and examine how the CG potentials vary with N (the number of CG segments on each chain) and how well the CG models can reproduce the structural and thermodynamic properties of the original system. Our strategy is quite general and versatile, is at least several orders of magnitude faster than those using many-chain simulations (thus effectively solving the transferability problem in coarse graining), and also avoids the problems caused by finite-size effects and statistical uncertainties in many-chain simulations commonly used in coarse graining. As two examples, we apply our strategy to the structure-based coarse graining of binary homopolymer blends and diblock copolymers. Our structure-based coarse graining preserves the critical point of symmetric binary blends and the mean-field order-disorder transition point of symmetric diblock copolymers at all coarse-graining levels, but cannot reproduce at any coarse-graining level the thermodynamic properties (i.e., the interchain internal energy per chain, the interchain virial pressure, and the change in the Helmoholtz free energy per chain from the athermal reference state) of the original system. The latter is simply due to the fact that the isotropic CG pair potentials (as commonly used) do not have the many-body nature of the potential of mean force caused by the coarse graining.