Model of viscous flow of glass-forming liquids and glasses

Glass transition criterion and plastic deformation of glass

“…Δε e , kJ/mol T g , K Table 1. Properties of NaPO3-MSO4 (M = Li, Na, K) sulfophosphate glasses and atom delocalization model parameters (data from [12]) Parameters RD and Rc have the meaning of atom delocalization energy Δεe when deriving the equations of viscosity (3) and (5) in the framework of the delocalized atom model and the activation theory of viscosity [2,15]:…”

“…For an amorphous cross-linked epoxy polymer, the activation volume of this relaxation process is obtained [23]: (16) In the delocalized atom model, the rate of the thermally stimulated recovery of the initial, undeformed state of glass (15) is determined by the rate of change in the number of delocalized atoms in this process:…”

Liquid-glass transition in the model of delocalized atoms

“…Substitution of this value to equality (12) gives the result (19) which means that the glass transition of a liquid (amorphous polymer) is a consequence of the rapid decrease ("freezing") in the relative number of excited delocalized atoms-quantum oscillators-to a mini mal value of ≈3% (Eq. (19)), at which a critically high "viscosity of glass transition" is reached (expression (1)): the viscous flow of the melt ceases.…”

“…As a glass forming melt cools, the relative number N e /N of delocalized atoms decreases according to the relation [12] , ( 4 ) where N is the total number of atoms. The temperature dependence of the free energy ΔF η (T) of activation of viscous flow of glass forming…”

“…(5)) is temperature independent, and the viscos ity is described by a classical Arrhenius exponential law [4,12]. The deviation from the Arrhenius behavior at low temperatures (T < θ) is commonly attributed to the cooperative nature of an elementary relaxation event.…”