STRUCTURALLY DETERMINED BROWNIAN DYNAMICS IN ORDERED COLLOIDAL SUSPENSIONS - SELF-DIFFUSION IN FLUID, SUPERCOOLED, AND CRYSTALLINE PHASES

Electrostatically interacting colloidal suspensions at medium to very low salt concentrations were prepared in differently ordered phases us ing the method of continuous deionization. Equilibrium phase states in clude fluid, mono- and polycrystalline material as well as coexistence between fluid and monocrystal. A nonequilibrium supercooled fluid sta te is reproducibly reached by shear melting. In these phases the long time self-diffusion coefficient D(L) Was measured by forced Rayleigh s cattering, while the potential of interaction was systematically varie d by changing salt concentration c(s) and volume fraction phi. In the equilibrium fluid D(L) decreases by roughly an order of magnitude as t he interaction increases. This trend extends continuously into the sup ercooled state. In all cases crystallization is observed for D(L)/D0 l ess-than-or-equal-to 0.10(1). In the polycrystalline phases self-diffu sion coefficients are still 1 to 2 orders of magnitude lower than in t he supercooled state. Here self-diffusion increases with increasing in teraction. For the monocrystalline case upper limits of D(L) are given . These data on the solid phases are discussed in terms of grain bound ary and vacancy diffusion.