On the dynamical instability in metastable liquids

The claim of Schneider et al. that a supercooled liquid transforms into a solid over a soft relaxational mode at the instability temperature is investigated within linear-response theory based on Zwanzig-Mori formalism. We have used two non-mean-field approximations and they confirm the view held by Schneider et al. Our studies reveal, however, that the stability limit temperature can be predicted reliably only over a knowledge of the point of divergence of the static structure factor. The experiments of Suck et al. which apparently disprove the theory of Schneider et al. are critically discussed in view of the constraint imposed by the surface coating on the free volume of the system. It is suggested that the soft relaxational mode drives the system into a state which is superplastic at the instability temperature.