Nonequilibrium Structure of Colloidal Dumbbells under Oscillatory Shear

TL;DR

This study uses Brownian dynamics simulations to explore how dense suspensions of anisotropic colloidal dumbbells respond to oscillatory shear, revealing phase transitions and dynamic slowing down related to particle shape and shear conditions.

Contribution

It extends previous work on nonequilibrium phase transitions in colloidal dumbbells to a broader range of aspect ratios and shear parameters, providing a detailed phase diagram.

Findings

Phase transitions occur at various aspect ratios under shear.

A nonequilibrium phase diagram summarizes transition behavior.

Higher aspect ratios lead to slower colloidal dynamics.

Abstract

We investigate the nonequilibrium behavior of dense, plastic-crystalline suspensions of mildly anisotropic colloidal hard dumbbells under the action of an oscillatory shear field by employing Brownian dynamics computer simulations. In particular, we extend previous investigations, where we uncovered novel nonequilibrium phase transitions, to other aspect ratios and to a larger nonequilibrium parameter space, that is, a wider range of strains and shear frequencies. We compare and discuss selected results in the context of novel scattering and rheological experiments. Both simulations and experiments demonstrate that the previously found transitions from the plastic crystal phase with increasing shear strain also occur at other aspect ratios. We explore the transition behavior in the strain-frequency phase and summarize it in a nonequilibrium phase diagram. Additionally, the experimental rheology results hint at a slowing down of the colloidal dynamics with higher aspect ratio.