Asynchronous Dynamics in Crosslinked Polymer Networks

Recently, we successfully applied time-temperature superposition to obtain master curves of the mean squared displacement (MSD) of atoms in a cross-linked epoxy using atomistic simulations. The resulting curves extend to a macroscopic time-scale (10⁹ s) and can be quantitatively compared with creep compliance obtained from experiments. Here, we show that the MSD trends of the center of mass of molecular units can also be superposed using identical shift factors. Comparison of the master curves and time-scaling exponents of different molecular moieties shows that units which differ in their topological constraints exhibit asynchronous dynamics. We call this feature topology-induced asynchronous (TIA) dynamics and define it as the temporal difference in the dynamics of atoms in a network that vary in their topological constraints. TIA dynamics arise due to the interplay between the chemistry of the epoxy monomer and the cross-linker. We discuss the role of asynchronous dynamics in the thermomechanical behavior of polymer networks composed of non-Gaussian monomers, and how chemistry-specific topological details are important for controlling the polymer dynamics.