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

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 $T_{\ast }$ 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 $\beta$-relaxation theory (SBR).

References in corpus (10)

• Theoretical perspective on the glass transition and amorphous materials
• Direct measurements of growing amorphous order and non-monotonic dynamic correlations in a colloidal glass-former
• Mosaic multi-state scenario vs. one-state description of supercooled liquids
• Mode-coupling theory for the slow collective dynamics of fluids adsorbed in disordered porous media
• Finite size effects in the dynamics of glass-forming liquids
• Analytic determination of dynamical and mosaic length scales in a Kac glass model
• Multiple length and time scales of dynamic heterogeneities in model glass-forming liquids: A systematic analysis of multi-point and multi-time correlations
• Anomalous layering at the liquid Sn surface
• Long-wavelength fluctuations lead to a model of the glass crossover
• Super-Cooled Liquids: Equivalence between Mode-Coupling Theory and Replica Approach