Macroscopic rotation of active colloids in a colloid-polymer mixture confined inside a spherical cavity

TL;DR

This study uses Molecular Dynamics simulations to explore how active colloids induce macroscopic rotation in a confined colloid-polymer mixture, revealing dynamic shape changes and motion driven by activity.

Contribution

It demonstrates how active colloids cause a macroscopic rotation and shape transformation in a confined colloid-polymer system, a novel insight into active matter behavior.

Findings

Active colloids induce a rotating ellipsoidal polymer-rich domain.

The colloid-rich domain attains macroscopic angular momentum.

The orientation of the rotating domain evolves via diffusion.

Abstract

From studies via Molecular Dynamics simulations, we report results on structure and dynamics in mixtures of active colloids and passive polymers that are confined inside a spherical container with a repulsive boundary. Such systems mimic the presence of bacteria in the background of bio-polymers. All interactions in the fully passive case are chosen in such a way that in equilibrium coexistence between colloid-rich and polymer-rich phases occurs. For most part of the studies the chosen compositions give rise to Janus structure; one side of the sphere is occupied by the colloids and the rest by the polymers. This partially wet situation mimics nearly a neutral wall in the fully passive scenario. Following the introduction of a velocity-aligning activity to the colloids, the shape of the polymer-rich domain changes to that of an ellipsoid, around the long axis of which the colloid-rich domain attains a macroscopic angular momentum. In the steady state, the orientation of this axis evolves via diffusion, implying that the passive domain is set into motion as well by the active particles.