Effective temperatures from the fluctuation-dissipation measurements in soft glassy materials

¹  Van Der Waals Zeeman Institut, Universiteit van Amsterdam - Valckenierstraat 65, 1018 XE, Amsterdam, The Netherlands, EU
²  Theoretical Physics and Polymer Group, Department of Applied Physics, Technische Universiteit Eindhoven 5600MB Eindhoven, The Netherlands, EU
³  Department of Physics and Astronomy, Vrije Universiteit Amsterdam - De Boelelaan 1081, 1081HV Amsterdam, The Netherlands, EU
⁴  Organization for the Promotion of Advanced Research, Kyushu University - Higashi-ku, Hakozaki 6-10-1, 812-0054 Fukuoka, Japan
⁵  Physikalisches Institut, Georg-August-Universität - Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, EU
⁶  Laboratoire de Physique Statistique, Ecole Normale Supérieure - 24, rue Lhomond, 75231 Paris Cedex 05, France, EU

Corresponding author: s.jabbari@tue.nl

Received: 21 April 2008
Accepted: 9 September 2008

Abstract

We have investigated the validity of the fluctuation-dissipation theorem (FDT) and the applicability of the concept of effective temperature in a number of non-equilibrium soft glassy materials. Using a combination of passive and active microrheology to measure displacement fluctuations and the mechanical response function of probe particles embedded in the materials, we have directly tested the validity of the FDT. Our results show no violation of the FDT over several decades in frequency (110⁴ Hz) for hard-sphere colloidal glasses and colloidal glasses and gels of Laponite. We further extended the bandwidth of our measurements to lower frequencies (down to 0.1 Hz) using video microscopy to measure the displacement fluctuations, again without finding any deviations from the FDT.