INDICATIONS FOR A CHANGE OF DIFFUSION MECHANISM IN SUPERCOOLED LIQUIDS

Indications for a crossover between two distinct dynamical regimes at a temperature Tc above the glass-transition temperature Tg are presented for simple supercooled liquids. (i) Relating diffusion coefficient D and reorientational correlation times with viscosity, a discontinuity for the temperature coefficient of / or 1/D is observed, demonstrating the failure of the Stokes-Einstein relations for T<Tc. (ii) Plotting NMR and dielectric correlation times on a reduced scale Tg/T shows that a bifurcation of the two relevant processes in a supercooled liquid (+ and 2 processes) appears for T<Tc. Tc is found at T/Tg=1.18e1.28. © 1990 The American Physical Society.