(379d) Dynamics of Repulsive and Attractive Colloidal Glasses Under Constant-Stress Deformation

External stresses can cause dense colloidal suspensions to exhibit shear melting, delayed yielding, creep, and other complex rheological behavior. Such phenomena are not only of utter practical and technological importance for the use and processing of colloid-based materials, but also play a role in the physics of dynamical arrest and jamming transitions in colloidal glasses and gels.  However, the underlying origins of these phenomena remain poorly understood without the ability to characterize in detail how the microstructure of these materials evolves during deformation under externally applied stresses. In this study, we use a custom-built shear cell coupled to a fast-scanning confocal microscope to directly visualize the creep deformation and yielding behavior of a dense colloidal suspension in which the interparticle interactions can be varied systematically from nearly hard-sphere to attractive. Investigation of particle rearrangements in response to different applied stresses allows us to capture and contrast the dynamic events that trigger the transition from slow, prolonged creep to liquid-like flow in both repulsive and attractive glasses. We will discuss our findings in light of the widely accepted bond- and cage-breaking yielding mechanisms in these systems.