Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition
Abstract
As the glass (in molecular fluidsDonth) or the jamming (in colloids and grainsLiuNature1998) transitions are approached, the dynamics slow down dramatically with no marked structural changes. Dynamical heterogeneity (DH) plays a crucial role: structural relaxation occurs through correlated rearrangements of particle ``blobs'' of size WeeksScience2000,DauchotPRL2005,Glotzer,Ediger. On approaching these transitions, grows in glass-formersGlotzer,Ediger, colloidsWeeksScience2000,BerthierScience2005, and driven granular materialsKeysNaturePhys2007 alike, strengthening the analogies between the glass and the jamming transitions. However, little is known yet on the behavior of DH very close to dynamical arrest. Here, we measure in colloids the maximum of a ``dynamical susceptibility'', *, whose growth is usually associated to that of LacevicPRE. * initially increases with volume fraction φ, as inKeysNaturePhys2007, but strikingly drops dramatically very close to jamming. We show that this unexpected behavior results from the competition between the growth of and the reduced particle displacements associated with rearrangements in very dense suspensions, unveiling a richer-than-expected scenario.