LONG-TIME SELF-DIFFUSION IN BINARY COLLOIDAL HARD-SPHERE DISPERSIONS

The long-time self-diffusion and phase behavior of a binary dispersion of hard spheres with a size ratio of 1:9.3 were studied. Labeling one of the particle species in the mixtures with a fluorescent dye allows for the measurement of its long-time self-diffusion coefficient using fluorescence recovery after photobleaching. Extensive measurements are reported for a wide range of volume fractions and mixture compositions. For high volume fractions, the data can be described by empirical formulas in which interactions of a tracer with particles of different sizes are effectively decoupled. The binary system shows a fluid-crystal type phase separation. No fluid-fluid phase separation is observed. At high volume fractions, two different glassy states are found. These two states could be distinguished by the separate measurement of the mobility of the small and the large spheres. In one of the glassy states, the small spheres remain mobile although the large spheres are structurally arrested. In the other, both particles are arrested.