Structure, compressibility factor and dynamics of highly size-asymmetric binary hard-disk liquids

TL;DR

This study uses molecular dynamics simulations to explore how adding small disks affects the structure, compressibility, and dynamics of highly size-asymmetric binary hard-disk liquids, revealing complex reentrant and glassy behaviors.

Contribution

It provides new insights into the structural and dynamic effects of small particles in size-asymmetric mixtures, highlighting phenomena like reentrant behavior and logarithmic relaxation.

Findings

Static correlations of large disks are weakly affected by small disks.

Compressibility factor exhibits non-monotonic dependence on small disk area fraction.

Relaxation times increase and show reentrant behavior at high large disk densities.

Abstract

By using event-driven molecular dynamics simulation, we investigate effects of varying the area fraction of the smaller component on structure, compressibility factor and dynamics of the highly size-asymmetric binary hard-disk liquids. We find that the static pair correlations of the large disks are only weakly perturbed by adding small disks. The higher-order static correlations of the large disks, by contrast, can be strongly affected. The compressibility factor of the system first decreases and then increases upon increasing the area fraction of the small disks and separating different contributions to it allows to rationalize this non-monotonic phenomenon. Furthermore, adding small disks can influence dynamics of the system in quantitative and qualitative ways. For the large disks, the structural relaxation time increases monotonically with increasing the area fraction of the small disks at low and moderate area fractions of the large disks. In particular, "reentrant" behavior appears at sufficiently high area fractions of the large disks, strongly resembling the reentrant glass transition in short-ranged attractive colloids and the inverted glass transition in binary hard spheres with large size disparity. By tuning the area fraction of the small disks, relaxation process for the small disks shows concave-to-convex crossover and logarithmic decay behavior, as found in other binary mixtures with large size disparity. Moreover, diffusion of both species is suppressed by adding small disks. Long-time diffusion for the small disks shows power-law-like behavior at sufficiently high area fractions of the small disks, which implies precursors of a glass transition for the large disks and a localization transition for the small disks. Therefore, our results demonstrate the generic dynamic features in highly size-asymmetric binary mixtures.