Predicting Several Seconds of the Relaxation Dynamics of an Entangled Polymer Melt from a Few Nanoseconds of Atomistic Molecular Dynamics

The rheology of high-molecular-weight polymer melts is determined by the entanglement dynamics. Polymer melts with hundreds of entanglements can have relaxation times on the order of several seconds. Predicting those relaxation dynamics from first principles requires bridging about eight orders of magnitude of time. This is a problem where coarse-graining is not only desirable but also necessary. The discrete slip-link model (DSM) is a hierarchy of strongly connected coarse-grained models that have great success predicting the linear and nonlinear rheology of high-molecular-weight polymers. Three of the four parameters of the most detailed DSM can be extracted from primitive path analysis. We have also recently shown how to extract the remaining friction parameter from atomistic simulations [J. Rheol. 64, 1035-1043 (2020)]. To illustrate the procedure, an available quantum chemistry-based force field for polyethylene oxide (PEO) was used to perform 100 ns of molecular dynamics (MD) simulations of a 12 kDa melt (8 entanglements). Then using the MD-extracted parameters, the DSM was used to predict several seconds of the relaxation dynamics of a 256 kDa PEO melt (171 entanglements). The predictions were compared to experiments performed at the same temperature.