Thermotaxis of Janus particles

Area of Science:

• Physics
• Materials Science
• Chemical Engineering

Background:

• Interactions of autonomous microswimmers are crucial for collective behaviors in motile active matter.
• Janus particles, with distinct hemispheric properties, are a common microswimmer design used to study these interactions.
• Tailoring surface chemistry and physics allows for fine-tuning particle interactions like attraction, repulsion, or alignment.

Purpose of the Study:

• To systematically investigate the interactions of Janus microswimmers.
• To quantify the orientation-dependent repulsion and alignment of a Janus particle in a thermal field.
• To develop a theoretical model explaining the observed dynamics based on thermoosmotic surface fluxes.

Main Methods:

• Monitoring the dynamics of a single gold-capped Janus particle.
• Utilizing an external temperature field generated by an optically heated metal nanoparticle.
• Developing a theoretical model for induced thermoosmotic surface fluxes.

Main Results:

• Quantified orientation-dependent repulsion and alignment of the Janus particle.
• Developed a simple theoretical model for thermoosmotic surface fluxes.
• The model indicates angular velocity depends on equatorial temperature profile and phoretic mobility contrast.
• Demonstrated that heterogeneous heat conductivity breaks apparent symmetry.

Conclusions:

• The study provides a detailed understanding of Janus particle interactions in thermal gradients.
• The theoretical model successfully explains the particle's angular velocity based on surface properties and temperature.
• Heterogeneous heat conductivity significantly influences microswimmer behavior and collective dynamics.