  We present an event-driven molecular dynamics study of glass formation in
two-dimensional binary mixtures composed of hard disks and hard ellipses, where
both types of particles have the same area. We demonstrate that characteristic
glass-formation behavior appears upon compression under appropriate conditions
in such systems. In particular, while a rotational glass transition occurs only
for the ellipses, both types of particles undergo a kinetic arrest in the
translational degrees of freedom at a single density. The translational
dynamics for the ellipses is found to be faster than that for the disks within
the same system, indicating that shape anisotropy promotes the translational
motion of particles. We further examine the influence of mixture's composition
and aspect ratio on the glass formation. For the mixtures with an ellipse
aspect ratio of $k=2$, both translational and rotational glass transition
densities decrease with increasing the disk concentration at a similar rate and
hence, the two glass transitions remain close to each other at all
concentrations investigated. By elevating $k$, however, the rotational glass
transition density diminishes at a faster rate than the translational one,
leading to the formation of an orientational glass for the ellipses between the
two transitions. Our simulations imply that mixtures of particles with
different shapes emerge as a promising model for probing the role of particle
shape in determining the properties of glass-forming liquids. Furthermore, our
work illustrates the potential of using knowledge concerning the dependence of
glass-formation properties on mixture's composition and particle shape to
assist in the rational design of amorphous materials.

Soft Condensed Matter