A density scaling conjecture for aging glasses

The aging rate of glasses has traditionally been modeled as a function of temperature, T, and fictive temperature, while density, ρ, is not explicitly included as a parameter. However, this description does not naturally connect to the modern understanding of what governs the relaxation rate in equilibrium. In equilibrium, it is well known that the relaxation rate, γ_eq, depends on temperature and density. In addition, a large class of systems obeys density scaling, which means the rate specifically depends on the scaling parameter, Γ = e(ρ)/T, where e(ρ) is a system specific function. This paper presents a generalization of the fictive temperature concept in terms of a fictive scaling parameter, Γ_fic, and a density scaling conjecture for aging glasses in which the aging rate depends on Γ and Γ_fic.