Crowding-Enhanced Diffusion: An Exact Theory for Highly Entangled Self-Propelled Stiff Filaments

Area of Science:

• Soft matter physics
• Active matter systems
• Statistical mechanics

Background:

• Understanding the behavior of crowded systems is crucial in various scientific fields.
• Self-propelled particles exhibit complex dynamics influenced by interactions and confinement.
• Previous models often focused on passive or less crowded systems.

Purpose of the Study:

• To investigate the interplay between crowding and self-propulsion in stiff filament systems.
• To explain the counterintuitive phenomenon of enhanced diffusion in dense active matter.
• To develop a predictive theoretical framework for active filament dynamics.

Main Methods:

• Event-driven Brownian dynamics simulations of strongly interacting, self-propelled stiff filaments.
• Development of an analytical theory extending the confining tube concept.
• Derivation of a scaling theory for effective diffusivity.

Main Results:

• Observed a significant increase in effective diffusivity with higher filament number density.
• Rationalized the 'crowded is faster' behavior using an extended confining tube model.
• Developed a predictive scaling theory for diffusivity based on Péclet number and density.
• An exact expression accurately predicted spatiotemporal dynamics across various timescales.

Conclusions:

• Crowding can enhance the dynamics of active matter systems.
• The extended confining tube model provides a robust framework for understanding active filament behavior.
• The developed theory accurately captures diffusion, directed motion, and orientational relaxation.