Binary mixtures of rod-like colloids under shear: microscopically-based equilibrium theory and order--parameter dynamics

TL;DR

This paper develops a microscopically-based equilibrium and dynamic theory for binary mixtures of rod-like colloids under shear, revealing complex oscillatory and symmetry-breaking behaviors.

Contribution

It introduces a mesoscopic free energy functional derived from microscopic density functional theory and combines it with dynamic equations to analyze shear-induced behaviors.

Findings

Identification of stable isotropic and nematic phases based on composition and rod length.

Discovery of synchronized and symmetry-breaking oscillatory states under shear.

Analysis of how shear rate and coupling influence the dynamical states.

Abstract

This paper is concerned with the dynamics of a binary mixture of rod--like, repulsive colloidal particles driven out of equilibrium by means of a steady shear flow (Couette geometry). To this end we first derive, starting from a microscopic density functional in Parsons--Lee approximation, a mesoscopic free energy functional whose main variables are the orientational order parameter tensors. Based on this mesoscopic functional we then explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. Second, by combining the equilibrium theory with the Doi--Hess approach for the order parameter dynamics under shear, we investigate the orientational dynamics of binary mixtures for a range of shear rates and coupling parameters. We find a variety of dynamical states, including synchronized oscillatory states of the two components, but also symmetry breaking behavior where the components display different in--plane oscillatory states.