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arXiv · 2107.00918

Non-monotonic dynamic correlations beneath the surface of glass-forming liquids

Hailong Peng·Huashan Liu·Thomas Voigtmann
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Abstract

Collective motion over increasing length scales is a signature of the vitrification process of liquids. We demonstrate the emergence of distinct static and dynamic length scales probed near the free surface in fully equilibrated glass-forming liquid films, and their connection to the bulk properties of the system. In contrast to a monotonically growing static correlation length, the dynamic correlation length that measures the extent of surface-dynamics acceleration into the bulk, displays a striking non-monotonic temperature evolution that is robust also against changes in detailed interatomic interaction. The maximum of dynamic correlations defines a cross-over temperature $T_*$ that we show to agree with a morphological change of cooperative rearrangement regions (CRR) of fast particles in the bulk liquids. The cross-over occurs at a temperature larger than the critical temperature Tc of mode-coupling theory (MCT). We link it to the point where fast-particle motion decouples from structural relaxation that can be defined rigorously within a recent extension of MCT, the stochastic $β$-relaxation theory (SBR).

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Hailong Peng, Huashan Liu, Thomas Voigtmann. 2021-07-12. Non-monotonic dynamic correlations beneath the surface of glass-forming liquids. https://doi.org/10.1103/physrevlett.129.215501

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