Chiral separation of rotating robots through obstacle arrays

The interplay between active matter and environmental complexity can be applied to achieve complex functions ranging from rectification, separation, and capture to sorting of active particles. Here, we experimentally realize chiral separation of disk-shaped active rotors by using the interactions between the rotors and the obstacle array. Differently chiral active particles passing through the obstacle array exhibit opposite lateral drifts. The separation efficiency is excellent provided that the obstacle array is of sufficient length. The spin and longitudinal flow of the rotors and the friction between rotors and obstacles jointly determine the lateral drift of the rotors, thus leading to chiral separation. Furthermore, we propose a simple theoretical model, which captures the essential mechanism underlying the chiral separation and properly reproduces the experimental critical collision angle. This scheme could separate objects with static chiral structures, once an external source can power the objects to spin with different angular velocities.