Thermotaxis of Janus Particles
Sven Auschra, Andreas Bregulla, Klaus Kroy, Frank Cichos

TL;DR
This study investigates how Janus particles respond to temperature gradients, revealing how their orientation and movement are influenced by surface properties and external thermal fields, with implications for active matter control.
Contribution
It provides a detailed analysis of thermotactic behavior of Janus particles, introducing a theoretical model linking temperature profiles to particle orientation and motion.
Findings
Orientation-dependent repulsion and alignment observed.
Theoretical model explains angular velocity based on temperature profile.
Heterogeneous heat conductivity breaks symmetry in temperature field.
Abstract
The interactions of autonomous microswimmers play an important role for the formation of collective states of motile active matter. We study them in detail for the common microswimmer-design of two-faced Janus spheres with hemispheres made from different materials. Their chemical and physical surface properties may be tailored to fine-tune their mutual attractive, repulsive or aligning behavior. To investigate these effects systematically, we monitor the dynamics of a single gold-capped Janus particle in the external temperature field created by an optically heated metal nanoparticle. We quantify the orientation-dependent repulsion and alignment of the Janus particle and explain it in terms of a simple theoretical model for the induced thermoosmotic surface fluxes. The model reveals that the particle's angular velocity is solely determined by the temperature profile on the equator…
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