Revealing the relationship between liquid fragility and medium-range order in silicate glasses

Abstract

Despite decades of studies, the nature of the glass transition remains elusive. In particular, the sharpness of the dynamical arrest of a melt at the glass transition is captured by its fragility. Here, we reveal that fragility is governed by the medium-range order structure. Based on neutron-diffraction data for a series of aluminosilicate glasses, we propose a measurable structural parameter that features a strong inverse correlation with fragility, namely, the average medium-range distance (MRD). We use in-situ high-temperature neutron-scattering data to discuss the physical origin of this correlation. We argue that glasses exhibiting low MRD values present an excess of small network rings. Such rings are unstable and deform more readily with changes in temperature, which tends to increase fragility. These results reveal that the sharpness of the dynamical arrest experienced by a silicate glass at the glass transition is surprisingly encoded into the stability of rings in its network.

Cyclic Peptide High-Entropy Noncovalent Glass

“…These values are close to those of most polymers, some small organic molecules with abundant aromatic groups, and inorganic glass formers with strong ionic interactions 41,42 . Yet, these values markedly deviate from those of traditional silicate glass-formers, water, and small organic molecules with strong hydrogen bonding interactions 41,[43][44][45] . This disparity can be ascribed to the synergy of hydrogen bonds, aromatic interactions, and hydrophobic effects 3,46 .…”

A Molecular‐Scale Origin of Shear Thinning and Brittle Failure of Silicate Melt

“…Moreover, small rings in sodium silicate glass are mechanically robust and can withstand large internal stresses (Song et al, 2019). Shi et al (2022) proposed that the presence of these strong but unstable small rings in silicate glass and supercooled melts may be the origin of their fragility. Therefore, when the deformation fluctuates in the sample under compression, the local structural relaxation and viscous reduction could be driven by the change in the ring sizes from unstable small rings to stable large rings, resulting in the localization of deformation and finally shear thinning and failure of a bulk sample.…”

Effect of calcium and potassium oxide addition on the viscosity and fragility of a calcium aluminosilicate melt

“…49 Molecular dynamics simulations indicate that large rings (e.g., six-membered rings) are flexible and stress-free, with no internal driving force for structural deformation, whereas smaller rings are relatively strained and thus may exhibit internal stress. 60 Shi et al 60 proposed the average mediumrange distance (MRD/Å), which is an indicator of ring size distribution. MRD/Å may be calculated using the following equation: 𝑀𝑅𝐷∕Å = 𝑓 ≤4 ring × 3.15 + 𝑓 5 ring × 3.70 + 𝑓 ≥6 ring × 4.30 (9) where 𝑓 m ring is the relative fraction of the m-membered ring, which can be determined from the total neutron scattering of the sample.…”