Fluctuations in an aging system: the absence of an effective temperature in the sol–gel transition of a quenched gelatin sample

Antoine Bérut (1) , Artyom Petrosyan (1) , Juan Ruben Gomez-Solano (1) , Sergio Ciliberto (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon

We study the fluctuations of a Brownian micro particle trapped with optical tweezers in a gelatin solution undergoing a fast local temperature quench below the sol-gel transition. Contrary to what was previously reported, we observe no anomalous fluctuations in the particle's position that could be interpreted in terms of an effective temperature. A careful analysis with ensemble averages shows only equilibrium-like properties for the fluctuations, even though the system is clearly aging. We also provide a detailed discussion on possible artifacts that could have been interpreted as an effective temperature, such as the presence of a drift or a mixing in time and ensemble averages in data analysis. These considerations are of general interest when dealing with non-ergodic or non-stationary systems.

Keywords: Brownian Motion; Disordered Systems; Gel colloïdal; Ergodicity breaking

Domains: Physics [physics]; Condensed Matter [cond-mat]; Statistical Mechanics [cond-mat.stat-mech]

Antoine Bérut, Artyom Petrosyan, Juan Ruben Gomez-Solano, Sergio Ciliberto. Fluctuations in an aging system: the absence of an effective temperature in the sol–gel transition of a quenched gelatin sample. Journal of Statistical Mechanics: Theory and Experiment, 2015, 2015 (10), pp.P10020. ⟨10.1088/1742-5468/2015/10/P10020⟩. ⟨ensl-01192667⟩