Clogging, dynamics, and reentrant fluid for active matter on periodic substrates

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Active matter systems exhibit unique collective behaviors not seen in equilibrium systems.
• Run-and-tumble particles are a key model for active matter, characterized by intermittent motion.
• Periodic obstacle arrays provide a controlled environment to study transport phenomena in active matter.

Purpose of the Study:

• To investigate the collective states and transport properties of run-and-tumble active matter disks driven over a periodic obstacle array.
• To identify and characterize different clogging behaviors and fluid states as a function of activity, driving force, and obstacle configuration.
• To understand the influence of driving direction and obstacle density on the emergent collective dynamics.

Main Methods:

• Numerical simulations of discrete run-and-tumble active matter disks.
• Systematic variation of key parameters: disk density, drift force, activity level, and obstacle array properties.
• Analysis of emergent states, including uniform liquid, clogged states, and clustered phases.
• Characterization of mobility and velocity-force relationships.

Main Results:

• Identified distinct clogging behaviors dependent on driving direction (symmetry vs. nonsymmetry) and activity level.
• Observed a clog-free uniform liquid at low activity along symmetry directions, transitioning to an active clogged state at higher activity.
• Characterized drive-dependent and drive-independent clogged states in nonsymmetry directions, with a reentrant fluid phase at low activity.
• Found that active clogged states are direction-independent, unlike thermal clogged states.
• Demonstrated that mobility is more robust against obstacle dilution at higher activities.

Conclusions:

• The collective behavior of active matter disks in periodic potentials is rich and highly sensitive to activity and driving conditions.
• Emergent clogging phenomena, including reentrant fluid phases and transitions to plastic-like flow, are key features of these systems.
• The study provides a comprehensive phase map of different collective states, offering insights into transport and self-organization in active matter.