Abstract
A pressure counterpart of the Vogel–Fulcher–Tammann (VFT) equation for representingthe evolution of dielectric relaxation times or related dynamic properties is discussed:τ(P) = τ0Pexp[DPΔP(P0−ΔP)], whereΔP = P−PSL,P0 is the ideal glasspressure estimation, DP is the pressure fragility strength coefficient, and the prefactorτ0P is related to the relaxation time at the stability limit(PSL)in the negative pressure domain. The discussion is extended to the Avramov model (AvM) relationτ(T,P) = τ0exp[ε(Tg(P)/T)D],supplemented with a modified Simon–Glatzel-type equation for the pressure dependence of the glasstemperature (Tg(P)), enabling an insight into the negative pressure region. A recently postulated (Dyre 2006Rev. Mod. Phys. 78 953) comparison between the VFT and the AvM-type descriptions isexamined, for both the temperature and the pressure paths. Finally, we address thequestion ‘Does fragility depend on pressure?’ from the title of Paluch M et al (2001J. Chem. Phys. 114 8048) and propose a pressure counterpart for the ‘Angellplot’.
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