Nonequilibrium Fluctuation Relation for Sheared Micellar Gel in a Jammed State

TL;DR

This study investigates shear rate fluctuations in a jammed micellar gel, demonstrating that the fluctuation relation can determine an effective temperature linked to the system's structural constraints, with size-dependent effects observed.

Contribution

The paper experimentally verifies a nonequilibrium fluctuation relation in a jammed micellar gel and introduces an effective temperature concept related to structural constraints.

Findings

Shear rate fluctuations are large and include negative values.

Probability distributions of power flux vary from Gaussian to non-Gaussian.

Effective temperature increases as system size decreases.

Abstract

We show that the shear rate at a fixed shear stress in a micellar gel in a jammed state exhibits large fluctuations, showing positive and negative values, with the mean shear rate being positive. The resulting probability distribution functions (PDF's) of the global power flux to the system vary from Gaussian to non-Gaussian, depending on the driving stress and in all cases show similar symmetry properties as predicted by Gallavotti-Cohen steady state fluctuation relation. The fluctuation relation allows us to determine an effective temperature related to the structural constraints of the jammed state. We have measured the stress dependence of the effective temperature. Further, experiments reveal that the effective temperature and the standard deviation of the shear rate fluctuations increase with the decrease of the system size.