Hydrodynamic capture of microswimmers into sphere-bound orbits

Area of Science:

• Physics
• Materials Science
• Chemical Engineering

Background:

• Self-propelled particles exhibit complex non-equilibrium behaviors.
• Interactions between active particles and obstacles are a key research area.

Purpose of the Study:

• To investigate the interaction between chemically propelled micro-rods and solid spheres.
• To understand the capture dynamics and orbital motion of active particles around passive objects.

Main Methods:

• Experimental observation of micro-rod and sphere interactions.
• Theoretical modeling using lubrication theory for phoretic propulsion.
• Analysis of particle speed and interaction range.

Main Results:

• Micro-rods are captured into stable, close orbits around solid spheres.
• Capture occurs at short range, independent of sphere material or size relative to particle length.
• Particle speed remains largely unchanged during capture and orbital motion.
• Model confirms capture and speed independence.

Conclusions:

• Activity-driven interactions are crucial for understanding self-propelled particle behavior near passive objects.
• The findings challenge the use of colloidal tracers for probing active matter systems.
• This work highlights the importance of particle-object interactions in active matter physics.