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: tau(P)=tau(P)(0) exp[D-P Delta P(P-0-Delta P)],where Delta P=P-P-SL, P-0 is the ideal glass pressure estimation, D-P is the pressure fragility strength coefficient, and the prefactor tau(P)(0) is related to the relaxation time at the stability limit (P-SL) in the negative pressure domain. The discussion is extended to the Avramov model (AvM) relation tau(T, P) = tau(0) exp[epsilon(T-g(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'.