Self-Propelled Janus Colloids in Shear Flow

TL;DR

This study investigates how self-propelled Janus colloids respond to shear flow, revealing transitions from random motion to flow-aligned migration driven by torque balance, with implications for controlling active particles in flow environments.

Contribution

It provides experimental insights into the behavior of active Janus particles under shear flow, highlighting the role of torque balance in their migration patterns.

Findings

Particles transition from random to flow-aligned motion with increasing shear.

Migration across streamlines occurs when self-propulsion and shear torques are comparable.

Particle behavior depends on propulsion speed and shear rate, enabling control of particle trajectories.

Abstract

To fully harness the potential of artificial active colloids, investigation of their response to various external stimuli including external flow is of great interest. Therefore, in this study, we perform experiments on SiO2-Pt Janus particles suspended in an aqueous medium in a capillary subjected to different shear flow rates. Particles were propelled using varied H2O2 (fuel) concentrations. For a particular propulsion speed, with increasing shear flow, a transition of motion of active Janus particles from the usual random active motion to preferential motion across stream-lines and then finally to migration along the flow, was observed. Our analysis revealed that these transitions are dictated by the torque due to the self-propulsion near wall w.r.t. shear-induced torque. Interestingly, we found that only when these torques are comparable, particles align in a manner such that they migrate significantly across the streamlines.