4.1 Article

Coarse-grained soft-clusters remain non-diffusing in the melt state

Journal

GIANT
Volume 8, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.giant.2021.100070

Keywords

3-dimensional architectured polymer; Dynamics; Cooperative glass; Polymer melts; giant molecules; soft-clusters

Funding

  1. Young Scientists Fund of the National Natural Science Foundation of China [21903013]
  2. Shanghai Municipal Education Commission

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The study focused on the melts of 3-dimensional dendritic beads-springs, revealing that soft-clusters composed of more than 200 beads cannot diffuse or relax above the glass transition temperature, although relaxation can happen on the level of beads. Each soft-cluster can only rotate in the cage formed by neighboring soft-clusters, and the non-diffusing state would transform to the liquid state at exceptionally high temperature.
Melts of 3-dimensional dendritic beads-springs, namely coarse-grained soft-clusters, are studied by molecular dynamics simulations. The goal is to elucidate the unique dynamics of giant molecules, and generally speaking, 3-dimensional architectured polymers. When constituted by more than the critical number around 200 beads, soft-clusters cannot diffuse or relax far above their glass transition temperature, although relaxation can happen on the level of beads. Each soft-cluster can only rotate in the cage formed by neighboring soft-clusters. Such a non-diffusing state would transform to the liquid state at exceptionally high temperature, e.g. 10 times the glass transition temperature. Agreeing with experiments, 3D hierarchies lead to unique dynamics, especially their divergent relaxation times with the number of beads. These unique dynamics are in sharp contrast with 1-dimensional chain-like polymers. We name such a special state as 'cooperative glass', because of the 'cooperation' of the 3D-connected beads. The design of soft-clusters may also resemble cooperative rearranging regions where cooperativeness is contributed by the low temperature, thus offer further insights into the glass problem.

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