Microscopic and thermodynamic origins of volume relaxation in soda-lime aluminosilicate glasses below the glass transition temperature

•Both experimental methods and MD simulations gave consistent results, with greater shrinkage and smaller β values obtained for the glass with more NBOs.•The Adam-Gibbs based equation for determining the volume relaxation time was proposed and validated.•The stericity of the rings resulted in a proportional shrinkage of annealing below Tg. The microscopic and thermodynamic features of structural relaxation below the glass transition temperature are still major unsolved problems in the field of glass science. In this study, we used both experimental and theoretical approaches to elucidate the role of non-bridging oxygens in the volume relaxation of soda-lime aluminosilicate glasses below the glass transition temperature. Both approaches yielded similar trends, with greater shrinkage observed for glasses with a higher number of non-bridging oxygens. Based on our findings, we proposed and validated a theoretical equation for determining the volume relaxation time. Molecular dynamics simulations also suggested that volume relaxation is affected by the stericity of the rings in the glass network.