Brownian motors via active granular bath

Abstract

Active matter composed of self-propelling bacteria, presents a new way of powering microdevices. However, such micro active systems are difficult to control and thus other model systems are being developed, for instance using active granular chains. We have performed experiments showing the net rotation of an asymmetric gear in a bath of active granular chains. We found that the rotation is due to the pushing of trapped active chains on trapping regions bounded by the boundaries of the gear. The resulting angular velocity was found to be zero at low numbers of active chains then increases linearly but saturates at high concentration and decreases furthermore. We attribute this dynamics on the interplay of the momentum transfer of the active chains on the gear as well as the available space in the trapping region and lastly from the effective viscosity of the granular medium.