Comment on "Correlations between isobaric and isochoric fragilities and thermodynamical scaling exponent for glass-forming liquids".
For nonassociated, glass-forming liquids and polymers, thermodynamic scaling of structural relaxation times and viscosities is an empirical fact, demonstrated by various groups for dozens of materials. The P and T invariance of the isochoric fragility follows directly from this scaling. Apparent inconsistencies with these statements were reported recently by Grzybowski [A. Grzybowski, K. Grzybowska, J. Zioło, and M. Paluch, Phys. Rev. E 74, 041503 (2006)]; however, the putative inconsistencies arise from use at higher pressures of parameters to correlate the isobaric and isochoric fragilities that are valid only for ambient pressure.
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