Non-equilibrium fluctuation-dissipation theorem in an aging colloidal glass
 

S. Jabbari-Farouji, D. Mizuno, M.Atokharrami, F.Mackintosh, C.F.Schmidt, E.Eiser, G.H.Wegdam, D.Bonn

We have studied the validity of the Stokes-Einstein relation as a special case of the fluctuation-dissipation theorem (FDT) in an aging colloidal glass. We have measured both the thermal fluctuations and the response function using passive and active microrheology. Contrary to theoretical suggestions our results show no deviations from FDT over several decades of frequency (1 -10 k Hz) during the whole of the aging process : from the low viscosity colloidal fluid to the elastic gel or glass phase.  In addition, our fndings unambiguously show that there exist two distinct slow modes in the later stages of aging. Our results illustrate convincingly the power  and possibilities of microrheology compared with traditional rheology : it is a non-invasive technique and covers a far wider bandwith.