Corresponding States Concept for Simple Supercooled Liquids Identifying a Change of Diffusion Mechanism above the Glass Transition Temperature

A corresponding states concept is applied to viscosity η and reorientational correlation times τ of simple supercooled liquids revealing a change of dynamics for a temperature T c well above the glass transition temperature T g . Reducing T by the minorly corrected T g an improved master plot for the viscosity results. An universal behaviour is discovered above 10 3 P whereas the viscosity follows individual curves below 10 3 P. A power law, η = A ( T — T c ), describes the individual curves with T c = 1.18 T g for all liquids. Above 10 3 P several approaches are checked. For NMR correlation times plotted on such an improved scale the bifurcation of the correlation times for the β and α process appears at T/T g = 1.18. The β process is an intrinsic feature of the universal viscous regime, only. The change of dynamics is also indicated by a breakdown of the Stokes‐Einstein relations. Comparing several supercooled liquids a discontinuity for τ/η and 1/( D η) as a function of 1/ T is found at T/T g = 1.19–1.25. In addition, arguments are given which support a cease of anisotropic reorientation in the viscous regime. All together, these indications favour the concept of the recent mode coupling theory where a dynamical phase transition is predicted above T g .