Brownian Dynamics Simulations of Liquid Glass

Abstract

Fluids of anisotropic particles have been under research for several decades as they give rise to some phase equilibria which do not exist in the spherical constituent fluids. Researchers usually concentrate on spherical interactions because their rotational symmetry is always preserved. However, the interactions in real fluids in nature and experiment are not completely spherical. Therefore, there is always a need to have insight on the structures and dynamics of fluids composed of anisotropic particles. Recently, a novel nonequilibrium glassy state was observed in experiment on hard-ellipsoid colloids which was a confirmation of the prediction of the Mode Coupling Theory (MCT) for the glass transition when solved for anisotropic fluids. This glassy state is now known as liquid glass (LG). In liquid glass, the centers of masses of the ellipsoids in the fluid can move freely while their rotation dynamics is arrested and thus cannot equilibrate. Using Brownian Dynamics (BD) simulations for ellipsoidal colloids, we could find liquid glass in simulations and compare its structures and dynamics to the experimental liquid glass. We also analyzed the liquid-glass correlation functions in simulations using the MCT universal solutions for ellipsoidal fluid. Moreover, we examine using BD simulations the translation-rotation (TR) decoupling in ellipsoidal colloids predicted by Perrin theory’s for diffusion in anisotropic fluid. The BD simulations were carried out for ellipsoids with different aspect ratios at low densities. The results of simulations agree with Perrin’s theoretical prediction. The TR decoupling is observed after the orientation motions of ellipsoids relax. On the other hand, the implementation of the double well (DW) potential as a model for the activation processes was investigated. We found that the large-timescale dynamics does not follow the power law relaxation predicted with MCT.