Check of the temperature- and pressure-dependent Cohen-Grest equation

The dynamics of a fragile glass-farmer (diglycidyl ether of bisphenol-A) ha s been studied by wideband dielectric spectroscopy down to the temperature- induced and the pressure-induced glass transition. A full check of the temp erature and pressure dependence of the structural relaxation time, predicte d within an extended free volume model by the generalised Cohen-Grest funct ion, is reported. From our investigation it is evident that this function s uitably describes the structural relaxation time at ambient pressure, but o n the other hand, it strikingly fails in describing the isothermal data und er variable pressure. (C) 2000 Elsevier Science B.V. All rights reserved.