Commentary on the temperature-dependent viscosity of supercooled liquids: a unified activation scenario

Recent progress in describing the viscosity of vitrified liquids through an effective temperature-dependent activation barrier offers a new look at the basis for classifying fragile and strong glasses. By considering the activated state kinetics of model fragile and strong liquids, we identify a common structure in the temperature variation of their activation barriers. A unified description is proposed in which all glass formers can exhibit strong and fragile behavior in principle, and correspondingly two strong-fragile dynamic crossovers are indicated. Our deductions are based only on atomistic calculations using specific interatomic interactions. Thus the results are model predictions subject to further studies and experimental confirmation. On the other hand, the justification for the method being used to obtain the effective activation barriers is based on a direct experimental test of the calculated viscosities.