Rheology of colloidal microphases in a model with competing interactions

TL;DR

This study investigates how different microphase structures in colloidal systems respond to shear, revealing distinct yielding behaviors for clusters, stripes, and crystals with bubbles through simulations.

Contribution

It provides a detailed analysis of the rheological response of various colloidal microphases under shear, highlighting the influence of microphase type on yielding mechanisms.

Findings

Clusters shear easily along layers with rotational assistance.

Parallel stripes shear smoothly; perpendicular stripes jam and reorient.

Crystals with bubbles fracture and form stripes under shear.

Abstract

We study the rheological properties of colloidal microphases in two dimensions simulating a model of colloidal particles with competing interactions. Due to the competition between short-range attraction and long-range repulsion, as a function of the density the model exhibits a variety of microphases such as clusters, stripes or crystals with bubbles. We prepare the system in a confined microphase employing Monte-Carlo simulations and then quench the system at T=0. The resulting configurations are then sheared by applying a drag force profile. We integrate numerically the equation of motion for the particles and analyze the dynamics as a function of the density and the applied strain rate. We measure the stress-strain curves and characterize the yielding of the colloidal microphases. The results depend on the type of microphase: (i) clusters are easily sheared along layers and the relative motion is assisted by rotations. (ii) Stripes shear easily when they are parallel to the flow and tend to jam when are perpendicular to it. Under a sufficiently strong shear rate perpendicular stripes orient in the flow direction. (iii) Crystals with bubbles yield by fracturing along the bubbles and eventually forming stripes. We discuss the role of dislocations, emitted by the bubbles, in the yielding process.