Dynamics and correlation length scales of a glass-forming liquid in quiescent and sheared conditions

TL;DR

This study investigates how dynamic heterogeneity and correlation length scales in a glass-forming colloidal liquid evolve under both quiescent and sheared conditions, revealing a persistent link between structure and slow dynamics.

Contribution

It extends four-point correlation analysis to sheared systems, showing that length scales relate to relaxation times under both equilibrium and nonequilibrium conditions.

Findings

Dynamic heterogeneity increases with relaxation time in quiescent liquids.

Correlation lengths follow a power-law with relaxation time in equilibrium.

Under shear, correlation lengths do not follow a simple power-law dependence.

Abstract

We numerically study dynamics and correlation length scales of a colloidal liquid in both quiescent and sheared conditions to further understand the origin of slow dynamics and dynamic heterogeneity in glass-forming systems. The simulation is performed in a weakly frustrated two-dimensional liquid, where locally preferred order is allowed to develop with increasing density. The four-point density correlations and bond-orientation correlations, which have been frequently used to capture dynamic and static length scales $\xi$ in a quiescent condition, can be readily extended to a system under steady shear in this case. In the absence of shear, we confirmed the previous findings that the dynamic slowing down accompanies the development of dynamic heterogeneity. The dynamic and static length scales increase with $\alpha$-relaxation time $\tau_{\alpha}$ as power-law $\xi\sim\tau_{\alpha}^{\mu}$ with $\mu>0$. In the presence of shear, both viscosity and $\tau_{\alpha}$ have power-law dependence on shear rate in the marked shear thinning regime. However, dependence of correlation lengths cannot be described by power laws in the same regime. Furthermore, the relation $\xi\sim\tau_{\alpha}^{\mu}$ between length scales and dynamics holds for not too strong shear where thermal fluctuations and external forces are both important in determining the properties of dense liquids. Thus, our results demonstrate a link between slow dynamics and structure in glass-forming liquids even under nonequilibrium conditions.