Corresponding states analysis for viscosity and nuclear magnetic resonance data in the glass transition regime

Abstract

The viscosity as a function of the temperature has been reanalyzed within a concept of corresponding states for organic glass-forming liquids including the viscous and fluid regime. A universal behavior is found for the viscosity in the range of 103 and up to 1014 P when the absolute temperature is reduced by the glass transition temperature Tg for each liquid. The master plot is significantly improved when minor corrections of Tg are introduced. Below 103 P, the liquids are characterized by individual properties. However, a power-law behavior, i.e. η=B+A(T−Tc)−γ, is found above a critical temperature Tc as predicted by the recent mode coupling theory with Tc =1.20 Tg for all studied systems. The exponent γ is found to be almost constant, i.e., γ=2.84±0.40, whereas A and B vary for the different systems. Hence, two different dynamical regimes above and below 103 P—separated by Tc —exist for a supercooled liquid which have to be described independently. In contrast to the cross-over regime near Tc , the curvature of η(T) above 103 P is rather small and several analytical descriptions have been checked to describe the master curve, but still not enough data are available to discriminate unambiguously between different approaches. The corresponding state analysis also holds for rotational correlation times τ in the range 10−12 s≤τ≤1 s as revealed by nuclear magnetic resonance (NMR) for three recently investigated organic liquids. In addition, the characteristic features of the nonexponential motional correlation function which have been used to describe the NMR results are discussed.