Hierarchical Procedure Bridging the Gap between Mesoscopic and Atomistic Simulations for Materials Design

A hierarchical procedure bridging the gap between atomistic and mesoscopic simulations for materials design is presented. A dissipative particle dynamics (DPD) is adopted for a mesoscopic simulation technique. In this method, a molecular structure is represented using a coarse-grained model, connecting soft spherical particles that correspond to a group of several atoms. The interaction parameters of the mesoscopic model, which are related to FloryHuggins χ-parameters, are estimated by calculating the energy of mixing for each pair of components in the atomistic simulation. Mesoscopic structures of the binary polymer blend are simulated with realistic χ-parameters using DPD. This bridging method from the atomistic to the mesoscopic level is applied to prediction of the mesoscopic structure of a hydrated polyelectrolyte membrane for fuel cells. The simulated structure of the membrane and its dependence on water content are in good agreement with experimental reports. For a reverse bridging method for different scale simulations, the molecular structure at the interface is extracted from the simulated mesoscopic structure by mapping atoms to the concentration profile of each component using a Monte Carlo technique. The complicated morphology of the binary polymer blend is successfully generated using this procedure. In the case of a hydrated polyelectrolyte membrane, an atomistic structure of a water channel is generated based on the mesoscopic structure. It is confirmed that the number of water molecules in the first coordination shell around the sulfonic acid group is of the same magnitude as the experimental study.