Multiscale Strategy for Predicting Radiation Chemistry in Polymers

Polymers are routinely subjected to ionizing radiation for sterilization, as part of planned usage, and as a driver for curing or to accelerate aging. A primary mode for radiation chemistry arises from ballistic electrons that induce electronic excitations, but subsequent chemical mechanisms are poorly understood. We develop a multiscale modeling strategy to predict this chemistry starting from quantum electrodynamics scattering calculations. Ensembles of nonadiabatic molecular dynamics simulations based on time-dependent density functional theory are used to sample initial bond-breaking events following the most likely excitations. These excited state configurations in turn feed into semiempirical quantum-based simulations of the approach towards chemical equilibrium. Application to polyethylene shows that local backbone conformation plays a significant role in the initial steps of radiolysis, providing an explanation for experimental observations of a morphology dependence in network crosslinking.