(553b) Heterogeneous Rouse Model Predictions for Linear Viscoelastic Response Functions in the Time-Temperature-Superposition Breakdown Regime

Since pioneering work by Plazek in the 1960’s, it has been known that time-temperature superposition breaks down in many polymers upon approach to the glass transition. 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 predictions of TTS breakdown by the Heterogeneous Rouse Model, which generalizes the Rouse model to incorporate dynamic heterogeneity – the emergence of a distribution of segmental relaxation times at low temperature. Predictions are in good agreement with simulations and with available experimentally observed relaxation spectra in the TTS-breakdown regime, suggesting that this theory provides a promising model for dynamics in the TTS breakdown regime.