PHASE-BEHAVIOR AND LONG-TIME SELF-DIFFUSION IN A BINARY HARD-SPHERE DISPERSION

We studied the phase behaviour of, and long-time self-diffusion in, a binary dispersion of hard spheres with a size ratio of 1:9.3. This sys tem exhibits a fluid-crystal-type phase separation. The fluid-solid bi nodal was determined by measurements of the compositions of coexisting phases, allowing a test of existing theories. By labelling either the large or the small, particles with a fluorescent dye the long-time se lf-diffusion coefficients of both particles could be measured separate ly using fluorescence recovery after photobleaching (FRAP). Systematic measurements were carried out for a wide range of volume fractions an d mixture compositions. The low volume fraction behaviour was compared with existing theory. For higher volume fractions formulae are propos ed that represent the data well. At the highest volume fractions long- time self-diffusion becomes arrested when the glass transition is reac hed. This is evidenced by an incomplete decay of the correlation funct ions that are measured with FRAP. Evidence was found for the existence of two different glassy states. In one of these both particles are st ructurally arrested. In the other, however, the small spheres remain m obile, although the large spheres are structurally arrested.