NON-FICKIAN DIFFUSION IN COLLOIDAL GLASSES

We have studied numerically the decay of the self-dynamic structure fa ctor (SDSF) for a small particle diffusing in a colloidal glass. We sh ow that, in line with theoretical predictions, the super-Burnett coeff icient (characterizing the deviation of the fourth moment of the singl e particle distribution from its Gaussian value) is finite. However, o ur results also show that large scale deviations from Fick's law of di ffusion should still be easy to detect experimentally. These deviation s take the form of the SDSF decaying algebraically rather than exponen tially as Fick's law would predict. (C) 1998 American Institute of Phy sics. [S0021-9606(98)50924-5].