Extended Fluctuation-Dissipation Theorem for Soft Matter in Stationary Flow

TL;DR

This paper extends the fluctuation-dissipation theorem to strongly driven soft matter systems in stationary flow, incorporating nonlinear effects and conjugate observables, supported by analytical and numerical results.

Contribution

It introduces an extended FDT applicable beyond linear response, linking stress fluctuations to conjugate observables in nonequilibrium steady states.

Findings

Extended FDT derived for Rouse polymers and colloidal suspensions.

Analytical and numerical validation of the extended FDT.

Suggests a generalization of Onsager's principle to nonequilibrium conditions.

Abstract

For soft matter systems strongly driven by stationary flow, we discuss an extended fluctuation-dissipation theorem (FDT). Beyond the linear response regime, the FDT for the stress acquires an additional contribution involving the observable that is conjugate to the strain rate with respect to the dissipation function. This extended FDT is evaluated both analytically for Rouse polymers and in numerical simulations for colloidal suspensions. More generally, our results suggest an extension of Onsager's regression principle to nonequilibrium steady states.