Chemically Driven Nano-Elastic Heterogeneities Control Fragility in Volcanic Melts

Here, the nanoscale structural drivers of the mechanical behavior of volcanic glasses are explored. The study spans a compositional series ranging from basalt to rhyolite, encompassing also technical glass-forming melts. Using a granular-medium framework, the vibrational and physical properties of synthetic silicate glass-forming melts are characterized. From these, this study quantifies the correlation length (ξ) and microscopic free volume (Vc), two parameters linked to the internal structural heterogeneity of the glass network. This study finds that both ξ and Vc systematically increase with silica content and show strong inverse correlations with elastic moduli and the melt fragility, highlighting how variations in medium-range order affect the elastic and viscous response of the melt. These results provide a quantitative framework to connect compositional changes with rheological behavior, offering new perspectives on how nanoscale structural features contribute to the mechanical evolution of silicate melts.