Size Dependence of Tracer Diffusion in Supercooled Liquids

We have determined by forced Rayleigh scattering the diffusion coefficients D of several photochromic tracers with van der Waals radii between 0.38 and 8 nm (the largest ones being photolabeled polystyrene micronetworks) in 10 glass-forming liquids at temperatures between the glass temperature T g and ∼1.2 T g . The results were analyzed in terms of power law plots, D ( T ) ∝ T /η( T ) ξ, where η is the solvent shear viscosity, and temperature shifts, D ( T ) ∝ T /η( T + Δ T ). The shift Δ T was related with the width of the rotational correlation time distribution via the time−temperature superposition principle.