Relaxation dynamics in a binary hard-ellipse liquid

TL;DR

This study investigates how binary hard-ellipse mixtures exhibit glassy dynamics similar to spherical particles, revealing the effects of size disparity and composition on translational and rotational relaxation near the glass transition.

Contribution

It demonstrates that binary hard-ellipse systems show universal relaxation behaviors influenced by size disparity and composition, extending understanding from spherical to anisotropic particles.

Findings

Rotational glass transition density is close to translational one.

Increasing size disparity speeds up long-time dynamics.

Different relaxation scenarios emerge with varying mixture compositions.

Abstract

Structural relaxation in binary hard spherical particles has been shown recently to exhibit a wealth of remarkable features when size disparity or mixture's composition is varied. In this paper, we test whether or not similar dynamical phenomena occur in glassy systems composed of binary hard ellipses. We demonstrate via event-driven molecular dynamics simulation that a binary hard-ellipse mixture with an aspect ratio of two and moderate size disparity displays characteristic glassy dynamics upon increasing density in both the translational and the rotational degrees of freedom. The rotational glass transition density is found to be close to the translational one for the binary mixtures investigated. More importantly, we assess the influence of size disparity and mixture's composition on the relaxation dynamics. We find that an increase of size disparity leads, both translationally and rotationally, to a speed up of the long-time dynamics in the supercooled regime so that both the translational and the rotational glass transition shift to higher densities. By increasing the number concentration of the small particles, the time evolution of both translational and rotational relaxation dynamics at high densities displays two qualitatively different scenarios, i.e., both the initial and the final part of the structural relaxation slow down for small size disparity, while the short-time dynamics still slows down but the final decay speeds up in the binary mixture with large size disparity. These findings are reminiscent of those observed in binary hard spherical particles. Therefore, our results suggest a universal mechanism for the influence of size disparity and mixture's composition on the structural relaxation in both isotropic and anisotropic particle systems.