Nonequilibrium phase transitions of sheared colloidal microphases: Results from dynamical density functional theory

TL;DR

This paper uses dynamical density functional theory to study how shear flow affects complex microphase structures in colloidal fluids with competing interactions, revealing shear-induced phase transitions and suppression of microphase separation.

Contribution

It demonstrates the impact of shear flow on microphase structures in colloids, showing shear-induced phase transitions and suppression of microphase separation, extending understanding beyond equilibrium behavior.

Findings

High shear rates suppress microphase separation.

Shear induces a transition from gyroid to cylindrical phases.

Colloidal systems show non-equilibrium relations to copolymer melts.

Abstract

By means of classical density functional theory and its dynamical extension, we consider a colloidal fluid with spherically-symmetric competing interactions, which are well known to exhibit a rich bulk phase behavior. This includes complex three-dimensional periodically ordered cluster phases such as lamellae, two-dimensional hexagonally packed cylinders, gyroid structures or spherical micelles. While the bulk phase behavior has been studied extensively in earlier work, in this paper we focus on such structures confined between planar repulsive walls under shear flow. For sufficiently high shear rates, we observe that microphase separation can become fully suppressed. For lower shear rates, however, we find that e.g. the gyroid structure undergoes a kinetic phase transition to a hexagonally packed cylindrical phase, which is found experimentally and theoretically in amphiphilic block copolymer systems. As such, besides the known similarities between the latter and colloidal systems regarding the equilibrium phase behavior, our work reveals further intriguing non-equilibrium relations between copolymer melts and colloidal fluids with competing interactions.