Tanis I, Karatasos K, Salez T. Molecular Dynamics Simulation of the Capillary Leveling of a Glass-Forming Liquid.
J Phys Chem B 2019;
123:8543-8549. [PMID:
31532672 DOI:
10.1021/acs.jpcb.9b05909]
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Abstract
Motivated by recent experimental studies probing (i) the existence of a mobile layer at the free surface of glasses and (ii) the capillary leveling of polymer nanofilms, we study the evolution of square-wave patterns at the free surface of a generic glass-forming binary Lennard-Jones mixture over a wide temperature range, by means of molecular dynamics simulations. The pattern's amplitude is monitored, and the associated decay rate is extracted. The evolution of the latter as a function of temperature exhibits a crossover between two distinct behaviors, over a temperature range typically bounded by the glass-transition temperature and the mode-coupling critical temperature. Layer-resolved analysis of the film particles' mean-squared displacements further shows that diffusion at the surface is considerably faster than in the bulk, below the glass-transition temperature. The diffusion coefficient of the surface particles is larger than its bulk counterpart by a factor that reaches 105 at the lowest temperature studied. This factor decreases upon heating, in agreement with recent experimental studies.
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