Fluctuation-dissipation theorem in an aging colloidal glass

TL;DR

This study experimentally tests the fluctuation-dissipation theorem in an aging colloidal glass using microrheology, finding no deviations from FDT and revealing two viscoelastic contributions that evolve with aging.

Contribution

It provides the first direct experimental verification of FDT in an aging colloidal glass over a broad frequency range, challenging previous reports of deviations.

Findings

No deviations from FDT over 1 Hz-10 kHz frequencies.

Identification of two distinct viscoelastic contributions.

Observation of a growing elastic response during aging.

Abstract

We provide a direct experimental test of the Stokes-Einstein relation as a special case of the fluctuation-dissipation theorem (FDT) in an aging colloidal glass. The use of combined active and passive microrheology allows us to independently measure both the correlation and response functions in this non-equilibrium situation. Contrary to previous reports, we find no deviations from the FDT over several decades in frequency (1 Hz-10 kHz) and for all aging times. In addition, we find two distinct viscoelastic contributions in the aging glass, including a nearly elastic response at low frequencies that grows during aging. This is the clearest change in material properties of the system with aging.