Dynamical modes of sheared confined microscale matter.

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Non-equilibrium Statistical Mechanics

Background:

• Understanding the complex dynamics of confined colloidal systems is crucial for materials science.
• Investigating non-equilibrium phenomena in driven soft matter provides fundamental insights into emergent behaviors.

Purpose of the Study:

• To investigate the non-equilibrium dynamics of a sheared colloidal cluster confined to a 2D disk.
• To identify and characterize distinct steady states and transitions within the system.
• To explore the role of slip events in the observed dynamics.

Main Methods:

• Utilizing overdamped Stokesian dynamics simulations.
• Conducting video microscopy experiments with paramagnetic and non-magnetic polystyrene particles.
• Employing time-shared optical tweezers for particle confinement.
• Applying external rotating magnetic fields to actuate paramagnetic particles.

Main Results:

• Identified two distinct steady states characterized by different mean angular velocities.
• Observed rare slip events where inner rings depinned from a static outer ring.
• Found bistability in mean angular velocities, linked to slip event analysis.
• Calculated particle waiting- and jumping time distributions, revealing a time scale between slips.
• Detected shear-thinning behavior and shear stress overshoots in the stress tensor components.

Conclusions:

• The study elucidates complex dynamics in sheared colloidal clusters, highlighting the significance of slip events.
• The observed transitions and bistability provide a framework for understanding non-equilibrium phenomena in confined soft matter.
• Findings contribute to the field of stochastic thermodynamics and suggest future research directions.