PhD position in nanomechanics of glasses

More sustainable glasses: investigation of the influence of hydration on mechanical properties of oxide glasses

Context

Water is abundant and ubiquitous, so improving the properties of materials using water molecules could be a sustainable method for synthesising structural materials. This idea is not new; exploiting the mechanical properties of nanostructured water in the form of hydroxides, molecules or clusters is in fact a biomimetic approach [1]. The mechanical properties of biological materials are constructively modulated by their molecular water content, as shown by the viscoelastic properties of collagen [2] or the fracture properties of spider silk [3]. Biological materials have a hierarchical structure, from the nanometric scale upwards, in which water plays a central role [4]. The structure and dynamics of water molecules in biological materials control their mechanical properties. In the case of oxide glasses, the absorption of water molecules could provide a solution to a long-standing problem: their fragility. The properties of these glasses derive essentially from their amorphous nanoscopic structure, where the insertion of water molecules plays a key role, influencing their mechanical properties [5,6]. Exposure to moisture and the associated ageing effect have also been explored, sometimes leading to significant strengthening [7]. The possibility of hydrating inorganic glasses up to 15% by mass using autoclave systems is now accessible, yet studies on mechanical properties are still limited to surface interactions with water, and not to global interactions. The consequences of this hydration therefore remain to be studied and understood.

Scientific challenge

The aim of this PhD thesis is to address the design of optimal material nano-architectures to exploit the mechanical potential of molecular water, by means of molecular dynamics and multi-scale simulation supplemented by structural characterisation experiments and mechanical properties at fracture. This approach is motivated by the recent results obtained on the influence of hydration on collagen microfibrils at the Institute (see figure) [8]. It is expected that the introduction of molecules will modify the nanoscopic architecture of glasses, favouring the creation of hydrogen bonds, and thus increase their energy dissipation at fracture, in other words their ductility. A typical example is the role of water in collagen, which acts sometimes as a glue and sometimes as a lubricant, depending on the level of hydration [2]. Models exist for the relationship between water content and mechanical properties, but it is not yet clear how the nanostructure of water controls specific mechanical properties. The same applies to the influence of the material's nano-architecture on the water structure.

References

[1] Chaplin et al., Nat. Rev. Mol. Cell Biol., 7, 2008; [2] Gautieri et al., J. Biomech., 45, 2012; [3] Yazawa et al., Commun. Mater., 1, 2020; [4] Meyers et al., Prog. Mater Sci., 53, 2008; [5] He et al., J. Non-Cryst. Solids X, 18, 2023; [6] Mei et al., Acta Mater., 178, 2019; [7] Liu et al., Phys. Rev. Mater., 4, 2020; [8] Vassaux et al. arXiv, 2312.12929, 2023