Field-driven dynamical demixing of binary mixtures

TL;DR

This paper demonstrates that in binary colloidal mixtures with different hydrodynamic radii, dynamical demixing can occur under an external field, especially when particle size differences are large, leading to long-lived transient states.

Contribution

It combines Brownian Dynamics and Dynamic Density Functional theory to reveal size-dependent dynamical demixing in colloidal mixtures under external fields.

Findings

Dynamical demixing occurs with large size differences.

Transient demixed states can be long-lived due to packing effects.

Thermodynamic mixing is maintained in the static field limit.

Abstract

We consider mixtures of two species of spherical colloidal particles that differ in their hydrodynamic radii, but are otherwise identical, in the presence of an external field. Since the particle-particle and particle-field interactions are the same for both species, they are completely mixed in the thermodynamic limit in the presence of any static field. Here, we combine Brownian Dynamics and Dynamic Density Functional theory of fluids to show that for sufficiently large differences in the hydrodynamic radius of the particles (and corresponding differences in their electrophoretic mobilities) dynamical demixing is observed. These demixed states are transient but, under certain conditions, packing effects compromise the relaxation towards the thermodynamic states and the lifetime of the demixed phases increases significantly.