Abstract
The fluctuation-dissipation theorem (FDT), a fundamental result of equilibrium statistical physics, can be violated when a system is taken out of equilibrium. A generalization of FDT has been theoretically proposed for out-of-equilibrium systems; the kinetic temperature entering the fluctuation-dissipation relation (FDR) is substituted by a time-scale-dependent effective temperature. We combine the measurements of the correlation function of the rotational dynamics of colloidal particles obtained via dynamic light scattering with those of the birefringence response to study the generalized FDR in an off-equilibrium Laponite suspension undergoing aging. (i) We find that the FDT is strongly violated in the early stage of the aging process and is gradually recovered as the aging time increases and (ii) we determine the aging-time evolution of the effective temperature, comparing our results with those of previous experiments.
Highlights
The study of the dynamics in nonequilibrium systems is an intriguing and fascinating area of modern physics
A generalization of FDT has been theoretically proposed for out-of-equilibrium systems; the kinetic temperature entering the fluctuation-dissipation relationFDRis substituted by a time-scale-dependent effective temperature
We combine the measurements of the correlation function of the rotational dynamics of colloidal particles obtained via dynamic light scattering with those of the birefringence response to study the generalized FDR in an off-equilibrium Laponite suspension undergoing aging. ͑i We find that the FDT is strongly violated in the early stage of the aging process and is gradually recovered as the aging time increases andiiwe determine the aging-time evolution of the effective temperature, comparing our results with those of previous experiments
Summary
The study of the dynamics in nonequilibrium systems is an intriguing and fascinating area of modern physics. Experiments in structural glasses are difficult because it is necessary to simultaneously measure a correlation function of a given variable and the associated response function, and all this in a systems that is instantaneously brought out of equilibrium. These difficulties are relaxed in the case of colloidal glassesor gels or jamsbecause the associated time scales are much longer and fall in the experimentally accessible window. Later a new series of experiments employed microrheology to measure the effective temperature of these colloidal systems These experiments studied the Brownian motion of probe particles added to the Laponite solution.
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