Slow dynamics and intermittent quakes in soft glassy systems

Abstract : We present measurements of the thermal fluctuations of the free surface of oil-in-water emulsions which exhibit a glassy behavior. The Surface Fluctuation Specular Reflection (SFSR) technique was applied to measure the free surface fluctuations. When the volume fraction of the oil droplets is close to or larger than the disordered packing volume fraction, the emulsion ages and its free surface exhibits abnormal fluctuations, consisting of rare but large amplitude quakes. From a statistical analysis of the signal, we observe that the relative importance of such intermittent quakes grows as the system ages. More precisely, we observe for the first time that the kurtosis of the fluctuations increases with aging time with an exponent of about 1.3. These quakes correspond to large changes in the local slope of the free surface over a few tenths of a second. We conjecture that such quakes reflect the dynamics peculiar to glassy systems driven by the relaxations of internal stress.