Slow dynamics, dynamic heterogeneities, and fragility of supercooled liquids confined in random media

TL;DR

This study uses molecular dynamics simulations to explore how supercooled liquids behave when confined in random media, revealing a transition from glass-like to Lorentz-gas-like dynamics and the effects of obstacle density on heterogeneity and fragility.

Contribution

It provides new insights into the dynamical crossover, heterogeneity suppression, and reentrant transitions in supercooled liquids confined by random obstacles, with protocol-dependent dynamics.

Findings

Increased obstacle density suppresses heterogeneity and promotes Arrhenius-like relaxation.

A reentrant transition from arrested to liquid phase occurs with increasing mobile particle density.

Dynamics depend on the protocol used to generate the random obstacle matrix.

Abstract

Using molecular dynamics simulations, we study the slow dynamics of supercooled liquids confined in a random matrix of immobile obstacles. We study the dynamical crossover from glass-like to Lorentz-gas-like behavior in terms of the density correlation function, the mean square displacement, the nonlinear dynamic susceptibility, the non-Gaussian parameter, and the fragility. Cooperative and spatially heterogeneous dynamics are suppressed as the obstacle density increases, which lead to the more Arrhenius-like behavior in the temperature dependence of the relaxation time. Our findings are qualitatively consistent with the results of recent experimental and numerical studies for various classes of spatially heterogeneous systems. We also investigate the dependence of the dynamics of mobile particles on the protocol to generate the random matrix. A reentrant transition from the arrested phase to the liquid phase as the mobile particle density {\it increases} is observed for a class of protocols. This reentrance is explained in terms of the distribution of the volume of the voids that are available to the mobile particles.