  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.
