Pattern Formation and Flocking for Particles Near the Jamming Transition on Resource Gradient Substrates

TL;DR

This study uses numerical simulations to explore how active and passive particles interact on resource substrates, revealing diverse pattern formations, phase separations, and flocking behaviors depending on system parameters.

Contribution

It introduces a comprehensive analysis of pattern formation and flocking in active-passive particle systems coupled to resource dynamics, highlighting new phases and behaviors.

Findings

Rich pattern forming phases observed at high densities

Active particles can undergo motility induced phase separation

Flocking behavior depends on density and resource rates

Abstract

We numerically examine a bidisperse system of active and passive particles coupled to a resource substrate. The active particles deplete the resource at a fixed rate and move toward regions with higher resources, while all of the particles interact sterically with each other. We show that at high densities, this system exhibits a rich variety of pattern forming phases along with directed motion or flocking as a function of the relative rates of resource absorption and consumption as well as the active to passive particle ratio. These include partial phase separation into rivers of active particles flowing through passive clusters, strongly phase separated states where the active particles induce crystallization of the passive particles, mixed jammed states, and fluctuating mixed fluid phases. For higher resource recovery rates, we demonstrate that the active particles can undergo motility induced phase separation, while at high densities, there can be a coherent flock containing only active particles or a solid mixture of active and passive particles. The directed flocking motion typically shows a transient in which the flow switches among different directions before settling into one direction, and there is a critical density below which flocking does not occur. We map out the different phases as function of system density, resource absorption and recovery rates,and the ratio of active to passive particles.