Simulation of Tracer Particle Diffusion in Attractive and Repulsive Glassy Matrices

Anomalous transport in confined systems is most commonly associated with particle sub-diffusion. Characterization of confined particle dynamics has been extended to matrices of different topologies, including ordered and disordered particles; the effects of slow relaxations of the confining matrix, however, have received comparatively little attention. We use event-driven molecular dynamics to scrutinize the diffusion of tracer particles confined within ”attractive” and “repulsive” glassy matrices, which are dominated by different relaxation dynamics and mechanisms, formed from a well-characterized, bi-disperse system of colloidal spheres with hard cores. These distinct relaxation processes strongly influence the dynamics and trajectories of the tracer particles. By varying the size of the tracer relative to that of a matrix particle, we investigate the role of size asymmetry on tracer dynamics. Because dispersing particles within slowly-relaxing matrices with varying interactions appear in settings ranging from the crowded cytoplasm inside cells to natural soils in the environment to artificial nanocomposites, these results provide insight into coupling between particle transport and matrix dynamics across a range of scientifically and technologically relevant processes.