Abstract

Density, Raman spectroscopy and viscosity measurements are utilized to probe, respectively, the volume, structural and shear relaxation behavior of a Na-Ca-Mg silicate glass of standard commercial float composition at ∼80 °C below its calorimetric glass transition. The results, when taken together, indicate that the lowering of fictive temperature of the glass during aging results in a Q-species disproportionation of the type Q2+Q4→2Q3, and all three relaxation processes are characterized by stretched exponential kinetics with similar average timescale (〈τ〉∼ 300 h) and stretching exponent (β ∼ 0.4), implying a close mechanistic relationship. It is hypothesized that the coexistence of strongly and weakly constrained domains or structural moieties in the network of a glass or supercooled liquid can give rise to a temporal decoupling between the structural and shear relaxation processes, as has been reported in some of the recent studies in the literature.

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