Glassy dynamics in monodisperse hard ellipsoids

Abstract

We present evidence from computer simulations for glassy dynamics in suspensions of monodisperse hard ellipsoids. In equilibrium, almost spherical ellipsoids show a first-order transition from an isotropic phase to a rotator phase. When overcompressing the isotropic phase into the rotator regime, we observe super-Arrhenius slowing-down of diffusion and relaxation, accompanied by two-step relaxation in positional and orientational correlators. The effects are strong enough for asymptotic laws of mode-coupling theory to apply. Glassy dynamics are unusual in monodisperse systems. Typically, polydispersity in size, a mixture of particle species or networkforming covalent bonds are prerequisite to prevent crystallization. Here, we show that a slight particle anisometry acts as a sufficient source of disorder. This sheds new light on the question of which ingredients are required for glass formation.

Glass transitions in monolayers of colloidal ellipsoids

“…Consequently γ T = 2.45±0.05 and γ θ = 2.33±0.05 for the translational and orientational correlations respectively. These values are close to the γ T = 2.3 measured for 3D ellipsoids [6]. In Fig.…”

“…5b shows that R T (t) for different q at φ = 0.77 collapse and keep ordered around the plateau region in F s (q,t), which confirms the validity of the MCT "factorization property" in the 2D colloidal ellipsoid suspensions. The "factorization property" has been observed in simulations of 3D Lennard-Jones particles [23] and 3D hard ellipsoids [6], but not in 2D systems before.…”

“…A recent simulation explored the dynamics around the glass transitions in 3D, but their ellipsoids have small aspect ratios (p = 1.25 prolate and 0.8 oblate), hence the two-step glass transition with the orientational glass was not able to be observed [6]. The only simulation about phase behaviors of 2D ellipses focused on the nematic order in small systems with 200 ellipses [7].…”

Glass Transitions in Quasi-Two-Dimensional Suspensions of Colloidal Ellipsoids

“…The glass transition of anisotropic particles has been studied in three dimensions (3D) mainly through simulation [7,8]. Molecular mode-coupling theory (MMCT) predicts that particle anisotropy should lead to new phenomena in glass transitions [9,10], and some of these have been observed in recent 3D simulations of hard ellipsoids [11,12]. MMCT [10,13] suggests that hard ellipsoids with an aspect ratio p > 2.5 in 3D can form an orientational glass in which rotational degrees of freedom become glass while the center-of-mass motion remains ergodic [9].…”

Crystallization in glassy suspensions of hard ellipsoids

“…However, the additional degree of freedom acts as a sufficiently strong source of disorder to introduce a glass transition. 5,6 We carried out Monte Carlo (MC) simulations of suspensions of monodisperse hard ellipsoids at constant number of particles N and constant external pressure P (the temperature T is constant too, but as the system is athermal T only enters the discussion as a trivial factor). Particles were propagated by local translation and rotation moves.…”