Two-Stage Ordering Kinetics in Binary Mixtures of Ellipsoidal Particles

Abstract

We investigate the nonequilibrium phase-ordering kinetics of a binary mixture of uniaxial ellipsoidal particles interacting via the anisotropic Gay-Berne potential using large-scale molecular dynamics simulations. Following a temperature quench from the isotropic and homogeneous phase into the coexistence region, the system exhibits two distinct ordering processes occurring on different time scales. At first, rapid orientational ordering leads to the formation and coarsening of nematic domains, characterized by dynamical scaling, generalized Porod-law behavior, and a growth law $\ell(t) \sim t^{1/2}$ consistent with nonconserved order-parameter dynamics. Later, the system undergoes binary phase separation driven by compositional fluctuations. This compositional ordering process shows a transition from diffusive growth $\ell(t) \sim t^{1/3}$ to hydrodynamic regimes, with finite-size scaling analysis indicating asymptotic viscous growth $\ell(t) \sim t$. Despite the presence of global orientational order, the phase-separation kinetics remains effectively isotropic. These results demonstrate a clear separation between orientational and compositional ordering dynamics, governed by distinct conservation laws, and provide a unified framework for understanding phase ordering in anisotropic particle systems.