14. Virtual Dynamic Mechanical Analysis

Dynamic mechanical analysis (DMA) provides insight into polymer viscoelastic behavior and its dependence on temperature. In that DMA is applied to a bulk sample, however, inferences about the connection among bulk and molecular behavior are generally speculative. In this work, a strain history similar to that of DMA is applied to atomistic polymer systems in silico. This method, termed Virtual DMA, can provide the data necessary to relate molecular information to bulk response. For example, strain amplitude can be varied to explore the effect of the corresponding small-scale perturbations on the stability of non-bond interactions. In some polymers, statistically significant differences in the glass transition temperature as measured by differential scanning calorimetry and DMA are found in physical experiments. When Virtual DMA results are compared with those from quasi-equilibrium cooling, the differing effects of imposed randomized and deterministic atomic velocities on molecular structure and local order can be identified.