A New Criterion for Glass Transition in Liquids in the Model of Excited Atoms

Application of the molecular dynamics method and the excited state model to the investigation of the glass transition in argon

“…The glass transition temperature T g ≈ 50 K is in reasonable agreement with the approximate empirical "two-thirds" rule [11] Now, we analyze the obtained data in terms of the excited state model [8,9]. In liquids and gases, a critical displacement of a kinetic unit (an atom or a group of atoms) ∆r m , which corresponds to a maximum of the interatomic attractive force F m (Fig.…”

“…This can be interpreted as the transition of argon to the amorphous vitreous state at T g ≈ 50 K [8].…”

“…The averaged fluctuation volume v f = V f /N per atom coincides in the physical meaning and the order of magnitude with the mean activation volume [expression (5)] and is determined by the mean displacement of the particle from the equilibrium position. Upon cooling of the liquid, the fraction of this (7) at the glass transition temperature reaches the minimum constant value f = f g [8,9] given by (8) The formation, migration, and disappearance of excited atoms are frozen at temperatures T < T g . Estimate (8) can be obtained by two or three independent methods, in particular, from the data on the viscosity in the vicinity of the glass transition point T g .…”

“…The approximate criterion (8) for the glass transition is satisfied for the majority of inorganic glasses, organic amorphous polymers, and metallic amorphous alloys [9]. However, there are deviations from this criterion for a number of glass-forming systems.…”

“…The fluctuation volume thus defined was compared with the corresponding quantity within the excited state model [8,9]. The glass transition point of argon was determined from the temperature dependence of the fluctuation volume fraction with the use of the molecular dynamics method.…”