SIZE DEPENDENCE OF TRACER DIFFUSION IN SUPERCOOLED LIQUIDS

We have determined by forced Rayleigh scattering the diffusion coeffic ients D of several photochromic tracers with van der Waals radii betwe en 0.38 and 8 nm (the largest ones being photolabeled polystyrene micr onetworks) in 10 glass-forming liquids at temperatures between the gla ss temperature T-g and similar to 1.2T(g) The results were analyzed in terms of power law plots, D(T) proportional to T/eta(T)(xi), where et a is the solvent shear viscosity, and temperature shifts, D(T) proport ional to T/eta(T + Delta T). The shift Delta T was related with the wi dth of the rotational correlation time distribution via the time-tempe rature superposition principle.