Heterogeneous Rouse Model for Polymer Dynamics and Linear Rheology in the Time-Temperature-Superposition-Breakdown Regime

Time-temperature superposition breaks down in many polymers upon approach to the glass transition temperature Tg. Because TTS is fundamentally rooted in the Rouse model prediction of a shared temperature dependence for chain and segmental relaxation modes, this breakdown implies a significant gap in our understanding of polymer dynamics at low temperature. Here, we report on tests against experiment of the Heterogeneous Rouse Model, which generalizes the Rouse model to incorporate the emergence of a distribution of segmental relaxation times at low temperature. The Heterogeneous Rouse Model predicts a compression of the Rouse regime in complex and relaxation moduli with increasing dynamic heterogeneity at lower temperatures. These predictions are found to be in agreement with observed polymer linear rheological response in the TTS-breakdown regime, suggesting that this theory provides a promising model for polymer TTS breakdown near Tg.