An equation for the description of volume and temperature dependences of the dynamics of supercooled liquids and polymer melts

A recently proposed expression to describe the temperature and volume dependences of the structural (or α  -) relaxation time is discussed. This equation satisfies the scaling law for the relaxation times,τ(T,V)=I(TVγ)τ(T,V)=I(TVγ), where T is temperature, V the specific volume, and γ   a material-dependent constant. The expression for the function I(TVγ)I(TVγ) is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover, providing a description of the dynamics with a minimal number of parameters. The results herein can be reconciled with previously found correlations of the isochoric fragility with both the isobaric fragility at atmospheric pressure and the scaling exponent γ.