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

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.