Chirality-induced directional rotation of a symmetric gear in a bath of chiral active particles

Abstract

We conduct a numerical study exploring the rotation of a symmetric gear driven by chiral particles in a two-dimensional box with periodic boundary conditions. The symmetric gear is submerged in a sea of chiral active particles. Surprisingly, even though the gear is perfectly symmetric, the microscopic random motion of chiral active particles can be converted into macroscopic directional rotation of the gear. (i) In the case of zero alignment interaction, the direction of rotation of the gear is determined by the chirality of active particles. Optimal parameters (the chirality, self-propelled speed, and packing traction) exist, at which the rotational speed reaches its maximum value. (ii) When considering a finite alignment interaction, alignment interactions between particles play an important role in driving the gear to rotate. The direction of rotation is dictated by the competition between the chirality of active particles and the alignment interactions between them. By tuning the system parameters, we can observe multiple rotation reversals. Our findings are relevant to understanding how the macroscopic rotation of a gear connects to the microscopic random motion of active particles.