Negative Entropy Production in Oscillatory Processes

TL;DR

This paper challenges the traditional view of the Second Law by showing that in viscoelastic fluids, instantaneous entropy production can be negative, but its time average remains nonnegative, supported by molecular dynamics simulations.

Contribution

It introduces a new derivation of the Second Law applicable to time-averaged entropy production, accommodating negative instantaneous values in oscillatory processes.

Findings

Instantaneous entropy production can be negative in viscoelastic fluids.

Time-averaged entropy production remains nonnegative.

Molecular dynamics simulations support the theoretical findings.

Abstract

Linear irreversible thermodynamics asserts that the instantaneous local spontaneous entropy production is always nonnegative. However for a viscoelastic fluid this is not always the case. Given the fundamental status of the Second Law, this presents a problem. We provide a new derivation of the Second Law, from first principles, which is valid for the appropriately time averaged entropy production allowing the instantaneous entropy production to be negative for short intervals of time. We show that time averages (rather than instantaneous values) of the entropy production are nonnegative. We illustrate this using molecular dynamics simulations of oscillatory shear.