Experimental observation of flow fields around active Janus spheres

Area of Science:

• Colloid science
• Soft matter physics
• Interfacial phenomena

Background:

• Phoretic mechanisms of asymmetric colloid propulsion are debated.
• Electrokinetic effects on platinum-polystyrene (Pt-PS) Janus sphere motility are under discussion.

Purpose of the Study:

• To probe the hydrodynamic flow field around a catalytically active colloid.
• To confirm a recently proposed propulsion mechanism for active colloids.
• To unify understanding of non-equilibrium interfacial transport processes.

Main Methods:

• Particle tracking velocimetry (PTV) was used to measure fluid velocity.
• Measurements were taken in both freely swimming and externally held stationary states.
• Hydrodynamic flow fields near the colloid surface were analyzed.

Main Results:

• Experimental data confirmed a specific mechanism for colloid propulsion.
• Detailed fluid velocity profiles around the active colloid were obtained.
• The study provides insights into non-equilibrium interfacial transport.

Conclusions:

• The findings confirm a key propulsion mechanism for active colloids.
• Results facilitate a comprehensive understanding of hydrodynamic interactions between active particles.
• This work paves the way for studying the collective dynamics of active colloids.