On the molecular origin of the Slow Arrenhius Processes (SAP) responsible for fast equilibration of polymer melts*

Growing experimental evidence indicates the presence of equilibration pathways exhibiting a temperature-invariant activation energy on the order of 100 kJ/mol. By exploiting the Onsager regression hypothesis, we identified the underlying molecular process responsible for this class of Arrhenius equilibration mechanisms with a slow mode (SAP), universally present in the liquid dynamics [1]. The SAP, which we show is intimately connected to high temperature flow, can efficiently drive melts and glasses towards more stable, less energetic states. Based on new experimental evidence, we propose that the SAP originate from rearrangements within a set of molecules organized in clusters which are less sensitive to density than the structural process, and do not undergo a glass transition. Measurements in nanoconfined polymer provided information on the volume distribution of the clusters and their average size. Depending on the system investigated, such clusters extends from several tens of nanometers up to more than a micron. We anticipate a correlation between the characteristic lengthscale of the SAP and its efficiency in equilibrating polymer melts.