Multiple dynamic regimes in concentrated microgel systems - Condensed Matter > Soft Condensed MatterReportar como inadecuado

Multiple dynamic regimes in concentrated microgel systems - Condensed Matter > Soft Condensed Matter - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Abstract: We investigate dynamical heterogeneities in the collective relaxation of aconcentrated microgel system, for which the packing fraction can beconveniently varied by changing the temperature. The packing fraction dependentmechanical properties are characterised by a fluid-solid transition, where thesystem properties switch from a viscous to an elastic low-frequency behaviour.Approaching this transition from below, we find that the range of spatialcorrelations in the dynamics increases. Beyond this transition, the spatialcorrelation range reaches a maximum, extending over the entire observablesystem size of approximately 5 mm. Increasing the packing fraction even furtherleads to a second transition, which is characterised by the development oflarge zones of lower and higher dynamical activity that are well separated fromeach other; the range of correlation decreases at this point. This strikingnon-monotonic dependence of the spatial correlation length on volume fractionis reminiscent of the behaviour recently observed at the jamming-rigiditytransition in granular systems Lechenault et al. 2008. We identify thissecond transition as the transition to -squeezed- states, where theconstituents of the system start to exert direct contact forces on each other,such that the dynamics becomes increasingly determined by imbalanced stresses.Evidence of this transition is also found in the frequency dependence of thestorage and loss moduli, which become increasingly coupled as direct frictionbetween the particles starts to contribute to the dissipative losses within thesystem. To our knowledge, our data provide the first observation of aqualitative change in dynamical heterogeneity as the dynamics switch frompurely thermally-driven to stress-driven.

Autor: David A. Sessoms FRIBPHYS, Irmgard Bischofberger FRIBPHYS, Luca Cipelletti LCVN, Véronique Trappe FRIBPHYS


Documentos relacionados