Angell plot

An Angell plot is a graphical representation used in glass physics to compare the temperature dependence of transport properties—typically viscosity or relaxation time—across different liquids. Invented by chemist C. Austen Angell, the plot uses scaled inverse temperature T_g/T on the horizontal axis and the logarithm of viscosity on the vertical axis, forcing all liquids to converge at the glass transition. The curvature of a liquid's trajectory on this plot reveals its fragility: strong liquids follow nearly Arrhenius behavior (straight lines), while fragile liquids exhibit dramatic curvature.

The Angell plot is not merely a visualization tool. It encodes the relationship between kinetic fragility and thermodynamic fragility—the correlation between how sharply a liquid's dynamics slow down and how rapidly its configurational entropy approaches the Kauzmann temperature limit. The plot suggests that the same microscopic mechanism governs both phenomena, though the precise connection remains debated.