Energy Renormalization for Coarse-Graining Polymers with Different Fragilities: Predictions from the Generalized Entropy Theory

摘要

Bottom-up prediction of physical performance of glass-forming (GF) polymers via coarse-grained (CG) modeling is challenging because these CG models normally experience significantly altered dynamics that strongly vary with temperature. Building upon the recently developed energy-renormalization (ER) coarse-graining method based on molecular dynamics simulations, generalized entropy theory (GET) is employed to theoretically investigate the influence of fundamental molecular parameters on CG modeling of polymers having different glass "fragilities" Taking a linear polymer melt as a model system within the GET framework, it is shown that the chain bending rigidity and cohesive interaction play critical roles in the glass formation of polymers and their CG analogs. To coarse-grain polymers having a higher fragility index, it requires greater magnitudes of ER factor epsilon(CG) to rescale the cohesive interaction strength under coarse-graining and thus recover the atomistic relaxation dynamics over a wide temperature range. The GET further predicts that a higher degree of coarse-graining generally requires greater magnitudes of epsilon(CG) due to the influence of loss of configuration entropy s(c) on the dynamics. GET analyses herein theoretically demonstrate the efficacy of the ER method toward building a multiscale temperature transferable modeling framework for GF polymers, and confirm the importance of preserving s(c) in CG modeling of dynamics of soft materials.