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, γeq, 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, Γfic, and a density scaling conjecture for aging glasses in which the aging rate depends on Γ and Γfic.