Little evidence for dynamic divergences in ultraviscous molecular liquids

The physics of the ultraviscous liquid phase preceding glass formation continues to pose major problems that remain unsolved. It is actively debated, for instance, whether the marked increase of the relaxation time reflects an underlying phase transition to a state of infinite relaxation time. To elucidate the empirical evidence for this intriguing scenario, some of the most accurate relaxation-time data available for any class of ultraviscous liquids-those obtained by dielectric relaxation experiments on organic liquids just above the glass transition-were compiled. Analysis of data for 42 liquids shows that there is no compelling evidence for the Vogel-Fulcher-Tammann (VFT) prediction that the relaxation time diverges at a finite temperature. We conclude that theories with a dynamic divergence of the VFT form lack a direct experimental basis.