Negative entropy production in oscillatory processes

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 rigorous derivation of the Second Law, 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. To cite this article: S.R. Williams et al., C. R. Physique 8 (2007).