Systematic and simulation-free coarse graining of multi-component polymeric systems: Structure-based coarse graining of binary polymer blends

Polymer blends have been extensively studied in many experimental, simulation, and theoretical analyses owing to their importance in engineering as well as polymer science. As opposed to homopolymer melts, only a few researchers have performed coarse graining of polymer blends. Professor Qiang Wang’s group from Colorado State University recently proposed a systematic and simulation-free method for coarse graining of homopolymer melts. The researchers used integral-equation theories instead of many-chain molecular simulations. This was in the quest to obtain structural as well as thermodynamic attributes of original and coarse-grained systems, and to examine quantitatively how the pair potentials between coarse-grained segments and the thermodynamic attributes varied with the coarse-graining level. The authors applied their method to both the structure-based and the relative-entropy-based coarse graining of homopolymer melts.

Professor Qiang Wang extended from their previous study and proposed a systematic and simulation-free strategy for the structure-based coarse graining of multi-component polymeric systems using the polymer reference interaction site model (PRISM) theory. He later applied it as an example to a simple model system of binary polymer blends. The developed structure-based coarse graining ensured that the original and coarse-grained systems have the same intermolecular correlation functions entailing the coarse-grain segments. When it was applied to binary polymer blends, it didn’t change the spinodal curve irrespective of the original model system as well as closure used.

In addition, the author also evaluated quantitatively how the effective non-bonded pair potentials between the coarse-grained segments and the thermodynamic attributes of coarse-grained system varied with the coarse-graining level. He observed that the structure-based coarse graining did not yield thermodynamic consistency between the original and coarse-grained systems at any coarse-graining level.

The method developed was quite general and versatile.  Therefore, it could be applied to more complex chain models as well as complicated systems. The new method was much faster than those applying many-chain molecular simulations, therefore, efficiently solving the transferability issue in coarse graining. It further avoided the issues caused by finite-size effects as well as statistical uncertainties in many-chain molecular simulations. The proposed method by Professor Qiang Wang in conjunction with fine graining served well for the goal of multi-scale modeling of multi-component polymeric systems. His research work is published in Polymer.