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 ar e reported for a wide range of volume fractions and mixture compositio ns. 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-crys tal type phase separation. No fluid-fluid phase separation is observed . At high volume fractions, two different glassy states are found. The se two states could be distinguished by the separate measurement of th e mobility of the small and the large spheres. In one of the glassy st ates, the small spheres remain mobile although the large spheres are s tructurally arrested. In the other, both particles are arrested.