Theoretical Limits of Energy Extraction in Active Fluids

Systems operating out of equilibrium can be maneuvered to perform mechanical work through feedback loops of information-to-energy conversion. Active materials form a class of far-from-equilibrium systems that are driven internally and have the capability of self-organization, which can be utilized to perform mechanical work. In this Letter we examine limits of work extraction from an active system by considering the transport of a particle coupled to the density field gradient of an active viscoelastic medium. The active energy is provided by a gliding activation front that converts a passive to an active medium. We demonstrate that the maximum extracted power undergoes a discontinuous transition to zero as the ratio of the activity and the activation rate exceeds a critical value. Our model provides a framework for designing efficient mechanisms of transport in synthetic materials.