  The dynamics of dense particle packings near the jamming transition is
characterized by correlated particle motion. The growth of dynamical
heterogeneities, or strong spatial variations in the motion of the particles
constituting the system, is a hallmark feature of slow glassy dynamics. We
report here a systematic confocal microscopy study that characterizes the
cooperative dynamics of fluorescently-labelled colloidal particles in dense
aqueous suspensions. We demonstrate that jammed particulate suspensions can be
fluidized by increasing the width of the particle size distribution. Our
molecular dynamics simulations, performed to numerically investigate the
effects of continuous-size polydispersity on dense particle packing dynamics,
show an excellent match with our experimental results. Besides shedding light
on the fundamental aspects of particle-scale dynamics at the jamming-unjamming
transition, our findings are significant in the processing of
commonly-encountered dense suspensions such as paints, cosmetics, and food.
