Fitting of viscosity: Distinguishing the temperature dependences predicted by various models of supercooled liquids

In an effort to assess the applicability of various competing theoretical models, we have examined the temperature dependence of the viscosity η(T) and of the α-relaxation times of a wide variety of supercooled liquids. The overall best fits over the entire temperature range above the glass-transition temperature and for all the diverse supercooled liquids investigated are given by the expression ln[η(T)/${\mathrm{\eta }}_{\mathrm{\infty }}$] =${\mathit{E}}_{\mathrm{\infty }}$+${\mathit{BT}}^{\mathrm{*}}$[(${\mathit{T}}^{\mathrm{*}}$-T)/${\mathit{T}}^{\mathrm{*}}$ ${]}^{8/3}$FTHETA (${\mathit{T}}^{\mathrm{*}}$-T), where FTHETA(${\mathit{T}}^{\mathrm{*}}$-T) is a step function that is 1 for T<${\mathit{T}}^{\mathrm{*}}$ and 0 for T>${\mathit{T}}^{\mathrm{*}}$, and ${\mathit{T}}^{\mathrm{*}}$ is usually greater than the melting point temperature. Our analysis supports the notion that there is a single dominant species-independent, nonmolecular mechanism underlying α relaxation for all supercooled liquids throughout the entire T-range characteristic of supercooled liquids. © 1996 The American Physical Society.