Probing an nonequilibrium Einstein relation in an aging colloidal glass

TL;DR

This paper experimentally investigates the effective temperature in an aging colloidal glass using a micrometric bead, revealing a non-monotonic temperature behavior linked to the system's relaxation dynamics.

Contribution

It provides the first direct measurement of a nonequilibrium effective temperature in an aging colloidal glass through a modified Einstein relation.

Findings

Effective temperature shows non-monotonic behavior during aging.

Deviation from Einstein relation correlates with relaxation times.

Effective temperature peaks and then decreases as the system ages.

Abstract

We present a direct experimental measurement of an effective temperature in a colloidal glass of Laponite, using a micrometric bead as a thermometer. The nonequilibrium fluctuation-dissipation relation, in the particular form of a modified Einstein relation, is investigated with diffusion and mobility measurements of the bead embedded in the glass. We observe an unusual non-monotonic behavior of the effective temperature : starting from the bath temperature, it is found to increase up to a maximum value, and then decreases back, as the system ages. We show that the observed deviation from the Einstein relation is related to the relaxation times previously measured in dynamic light scattering experiments.