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

Using molecular dynamics simulations, we study the slow dynamics of supercooled liquidsconfined in a random matrix of immobile obstacles. We study the dynamical crossover fromglass-like to Lorentz-gas-like behavior in terms of the density correlation function, the meansquare displacement, the nonlinear dynamic susceptibility, the non-Gaussian parameter, and thefragility. We find the cooperative and spatially heterogeneous dynamics to be suppressed as theobstacle density increases, leading to a more Arrhenius-like behavior in the temperaturedependence of the relaxation time. Our findings are qualitatively consistent with the results ofrecent experimental and numerical studies for various classes of spatially heterogeneoussystems. We also investigate the dependence of the dynamics of mobile particles on theprotocol used to generate the random matrix. A re-entrant transition from the arrested phase tothe liquid phase as the mobile particle density increases is observed for a class of protocols.This re-entrance is explained in terms of the distribution of the volume of the voids that areavailable to the mobile particles