A random walk description of the heterogeneous glassy dynamics of attractingcolloids

Abstract

We study the heterogeneous dynamics of attractive colloidal particles close to the geltransition using confocal microscopy experiments combined with a theoretical statisticalanalysis. We focus on single particle dynamics and show that the self-part ofthe van Hove distribution function is not the Gaussian expected for a Fickianprocess, but that it reflects instead the existence, at any given time, of colloidswith widely different mobilities. Our confocal microscopy measurements can bedescribed well by a simple analytical model based on a conventional continuoustime random walk picture, as already found for several other glassy materials. Inparticular, the theory successfully accounts for the presence of broad tails in the vanHove distributions that exhibit exponential, rather than Gaussian, decay at largedistance.