Active Brownian particles and run-and-tumble particles separate inside a maze

TL;DR

This study demonstrates that geometrical confinement in maze structures can effectively separate active Brownian particles from run-and-tumble particles, offering a new method for particle separation without chemical agents.

Contribution

We show through simulations that maze geometries can distinguish ABPs from RTPs based on their escape and accumulation behaviors, introducing a novel physical separation technique.

Findings

ABPs escape faster from the maze center than RTPs.

RTPs reach the maze center more easily from the rim.

ABPs accumulate at the outer regions of the maze.

Abstract

A diverse range of natural and artificial self-propelled particles are known and are used nowadays. Among them, active Brownian particles (ABPs) and run-and-tumble particles (RTPs) are two important classes. We numerically study non-interacting ABPs and RTPs strongly confined to different maze geometries in two dimensions. We demonstrate that by means of geometrical confinement alone, ABPs are separable from RTPs. By investigating Matryoshka-like mazes with nested shells, we show that a circular maze has the best filtration efficiency. Results on the mean first-passage time reveal that ABPs escape faster from the center of the maze, while RTPs reach the center from the rim more easily. According to our simulations and a rate theory, which we developed, ABPs in steady state accumulate in the outermost region of the Matryoshka-like mazes, while RTPs occupy all locations within the maze with nearly equal probability. These results suggest a novel technique for separating different types of self-propelled particles by designing appropriate confining geometries without using chemical or biological agents.