Dynamical heterogeneity in colloidal glasses

Three-dimensional particle movement in colloidal glasses was directly observed using confocal microscopy. By tracking the particles positions from these observations, it is shown that when the system’s density increases, the relaxation time increases. Additionally it was shown that colloidal glasses are characterized by correlated motion. The typical number of particles involved in correlated motion, represented by the dynamical susceptibility χ4, was then computed for different packing fractions, ranging from 0.54 to 0.60. χ4 depends on the probing length and the timescale on which the system is observed and has a maximum value at χ4(a∗, τ∗). This maximum value was compared for four different packing fractions. From these experiments it was concluded that the dynamical susceptibility grows with packing fraction.