Trochoidal trajectories of self-propelled Janus particles in a diverging laser beam

TL;DR

This paper demonstrates that Janus particles can be optically activated to follow trochoidal, rosette-like trajectories due to self-thermophoresis and optical torque, without chemical fuel.

Contribution

It introduces a model explaining the trochoidal trajectories of light-activated Janus particles, combining self-thermophoresis and optically-induced torque effects.

Findings

Janus particles exhibit trochoidal trajectories in diverging laser beams.

The proposed model accurately reproduces observed rosette patterns.

Optical activation enables controlled particle motion without chemical fuels.

Abstract

We describe colloidal Janus particles with metallic and dielectric faces that swim vigorously when illuminated by defocused optical tweezers without consuming any chemical fuel. Rather than wandering randomly, these optically-activated colloidal swimmers circulate back and forth through the beam of light, tracing out sinuous rosette patterns. We propose a model for this mode of light-activated transport that accounts for the observed behavior through a combination of self-thermophoresis and optically-induced torque. In the deterministic limit, this model yields trajectories that resemble rosette curves known as hypotrochoids.