Floor- or Ceiling-Sliding for Chemically Active, Gyrotactic, Sedimenting Janus Particles

Area of Science:

• Physics of active matter
• Soft condensed matter physics
• Colloidal science

Background:

• Chemically active particles self-propel via surface reactions, creating chemical fields and hydrodynamic flows.
• Interactions with confining surfaces lead to phenomena like wall-bound sliding states.
• Janus particles, often used as model systems, are typically gyrotactic and sediment.

Purpose of the Study:

• To theoretically investigate the occurrence of sliding states for gyrotactic, self-phoretic Janus particles near horizontal walls.
• To quantify the influence of gravity-induced effects (sedimentation, gyrotaxis) on particle-wall interactions.
• To construct phase diagrams mapping sliding states as a function of key physical parameters.

Main Methods:

• Theoretical modeling of chemically active Janus particles.
• Construction of state diagrams based on sedimentation velocity, gyrotactic response, and phoretic mobility.
• Comparison of theoretical predictions with experimental data.

Main Results:

• Sliding states can occur at horizontal walls (floors and ceilings).
• Simultaneous sliding at both floor and ceiling is possible under specific conditions.
• The parameter space reveals distinct regions for sliding at floor only, ceiling only, or no sliding states.
• Theoretical predictions show good agreement with experimental observations.

Conclusions:

• Gravity-induced effects significantly influence the wall-interaction behavior of active Janus particles.
• The study provides a framework for understanding and predicting sliding states in active matter systems.
• Experimental validation confirms the theoretical model's ability to capture complex particle dynamics near surfaces.