Work extraction and performance of colloidal heat engines in viscoelastic baths

TL;DR

This study explores how viscoelastic fluids influence the efficiency and power output of colloidal heat engines, showing that fluid memory effects can significantly enhance performance compared to viscous environments.

Contribution

It introduces a model analyzing the impact of viscoelasticity on colloidal heat engine performance during finite-time Stirling cycles, highlighting the role of fluid relaxation time.

Findings

Power and efficiency are enhanced in viscoelastic fluids.

The cycle time interval for positive power broadens with fluid relaxation time.

Transient friction effects are crucial in finite-duration thermodynamic cycles.

Abstract

A colloidal particle embedded in a fluid can be used as a microscopic heat engine by means of a sequence of cyclic transformations imposed by an optical trap. We investigate a model for the operation of such kind of Brownian engines when the surrounding medium is viscoelastic, which endows the particle dynamics with memory friction. We analyze the effect of the relaxation time of the fluid on the performance of the colloidal engine under finite-time Stirling cycles. We find that, due to the frequency-dependence of the friction in viscoelastic fluids, the mean power delivered by the engine and its efficiency can be highly enhanced as compared to those in a viscous environment with the same zero-shear viscosity. In addition, with increasing fluid relaxation time the interval of cycle times at which positive power output can be delivered by the engine broadens. Our results reveal the importance of the transient behavior of the friction experienced by a Brownian heat engine in a complex fluid, which cannot be neglected when driven by thermodynamic cycles of finite duration.