On the pressure evolution of dynamic properties of supercooled liquids

A pressure counterpart of the Vogel–Fulcher–Tammann (VFT) equation for representing the evolution of dielectric relaxation times or related dynamic properties is discussed: τ (P) = τ P0 exp[DPP(P0 − P)], where P = P − PSL, P0 is the ideal glass pressure estimation, DP is the pressure fragility strength coefficient, and the prefactor τ P0 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) relation τ (T, P) = τ0 exp[ε(Tg(P)/T)D], supplemented with a modified Simon–Glatzel-type equation for the pressure dependence of the glass temperature (Tg(P)), enabling an insight into the negative pressure region. A recently postulated (Dyre 2006 Rev. Mod. Phys. 78 953) comparison between the VFT and the AvM-type descriptions is examined, for both the temperature and the pressure paths. Finally, we address the question ‘Does fragility depend on pressure? ’ from the title of Paluch M et al (2001 J. Chem. Phys. 114 8048) and propose a pressure counterpart for the ‘Angell plot’. 1