Title: Visualization of shear banding in colloidal glasses

Vijayakumar Chikkadi, Gerard Wegadm, Bernard Nienhuis, Peter Schall - Febr 01 2010

Collaborators: Gerard Wegadm, Bernard Nienhuis, Peter Schall

Abstract

Shear banding, i.e. the localization of shear flow, occurs in a manifold of systems ranging from hard materials 
such as metallic glasses to soft materials such as clays, shaving cream or mayonnaise. We investigate this 
phenomenon in a dense colloidal system using confocal microscopy that enables to track individual particles 
in 3D space and time. The particle motions reveal a transition from homogeneous flow to shear localization 
above a critical shear rate. We elucidate this transition using spatial correlations in the displacement of 
the particles. The diffusive motion of the particles is correlated over large length, and shows intermittent, 
scale-free behavior, reminiscent of crystal plasticity. Further, we associate an order parameter with the mobility 
of particles and demonstrate that shear banding is phase coexistence of regions differing in mobilities.