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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 [1]. Numerous features of this Aslowing down@ are reasonably described [2] by the mode coupling theory (MCT) of supercooled liquids [3]. 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.
No. 6733


computer simulations, glass transition, polymers


Bennemann, C. , Donati, C. , Baschnagel, J. and Glotzer, S. (1999), Growing Range of Correlated Motion in a Polymer Melt on Cooling Towards the Glass Transition, Nature, [online], (Accessed May 30, 2024)


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Created April 30, 1999, Updated October 12, 2021