Growing Range of Correlated Motion in a Polymer Melt on Cooling Towards the Glass Transition
C Bennemann, C Donati, J Baschnagel, S C. Glotzer
Many liquids cooled to low temperatures form glasses (amorphous solids) instead of crystals. As the glass transition is approached, molecules become localized, or Acaged,@ and relaxation times increase by many order of magnitude . Numerous features of this Aslowing down@ are reasonably described  by the mode coupling theory (MCT) of supercooled liquids . The ideal form of this theory predicts a dynamical critical temperature Tc at which the molecules become permanently trapped in the Acage@ formed by their neighbors, and vitrification occurs. Although the sharp transition is actually avoided because molecules eventually escape their Acage,@ its signature can still be observed. Unlike conventional critical phenomena (e.g. a liquid-gas transition), the mode coupling transition is not accompanied by a diverging or even growing static correlation length. However, recent simulations [4-10] and experiments [11,12] show that liquids are dynamically heterogeneous, suggesting the possibility of a relevant Adynamical@ length scale. Here we investigate a simulated melt of short, unentangled polymers over a range of T where it is well described by MCT, and show that although density fluctuations remain short-ranged, spatial correlations between monomer displacements become long-ranged as Tc is approached on cooling.
, Donati, C.
, Baschnagel, J.
and Glotzer, S.
Growing Range of Correlated Motion in a Polymer Melt on Cooling Towards the Glass Transition, Nature, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851551
(Accessed June 6, 2023)