MEASURING DIFFUSION IN SUPERCOOLED LIQUIDS - THE EFFECT OF KINETIC INHOMOGENEITIES

There is growing evidence to suggest that cooperativity in glasses is characterized by a spatial distribution of relaxation times. In this p aper we examine the consequences of such inhomogeneities in the measur ement of translational and rotational diffusion constants. We find tha t the decay of a concentration profile (the basis of transient grating experiments) is accelerated by the development of additional gradient s parallel to the relaxation time gradients. This may account for rece ntly observed differences in the variation of rotational and translati onal diffusion constants with viscosity below the glass transition tem perature. The additional gradients may also provide the first direct m eans of examining the length scale associated with these inhomogeneiti es. (C) 1996 American Institute of Physics.