Active Particles in Tunable Compressible Environments

Area of Science:

• Soft Matter Physics
• Active Matter Systems
• Colloidal Science

Background:

• Active particles interact with and influence their surrounding environment.
• The interplay between active particle dynamics and environmental properties is complex and bidirectional.
• Controlling both active particle behavior and environmental mechanics simultaneously is challenging.

Purpose of the Study:

• To develop an experimental system for in situ simultaneous control of active particles and their environment.
• To investigate the effects of tunable environmental stiffness and particle activity on particle trajectories.
• To elucidate the mechanisms behind emergent chiral active motion and self-sustained reorientations.

Main Methods:

• Utilized a 2D bath of colloidal silica particles as the environment and gold-coated Janus spheres as active particles.
• Employed an external AC electric field applied orthogonally to the planar layer to tune system parameters.
• Analyzed active particle trajectories, focusing on rotational motion, reorientation frequency, and speed.

Main Results:

• Increasing electric field strength enhanced environmental stiffness and active particle speed.
• Active trajectories showed increased rotational motion with higher particle speeds.
• Observed emergent chiral active motion and demonstrated self-sustained reorientations driven by local compressions and interaction asymmetries.

Conclusions:

• The mechanical properties of the environment can be dynamically tuned to reshape active trajectories.
• Local compressions and interaction asymmetries provide a general particle-level mechanism for self-sustained reorientations in active matter.
• This work establishes a framework for studying the coupled dynamics of active particles and their tunable environments.