Transport and relaxation phenomena in highly viscous liquids

Temperature dependence of the viscosity of many glass-forming liquids is investigated over a wide range of temperatures (100 to 1700 K). It is shown that the three Vogel-Fulcher coefficients are not constant but exhibit regular variations versus temperature over the entire range 10^-3 to 10¹² Pl. This property is consistent with the nonlinear variations of the free-volume in the Cohen and Grest percolation model (1981, 1984). A similar result is found for the dielectric relaxation time in glycerol-water mixtures and in propylene carbonate.