Deformation of silica glass studied by molecular dynamics: Structural origin of the anisotropy and non-Newtonian behavior

A novel aspect of the medium-range structure of silica drawn into fibers is studied. The network of silica glass structure is composed of corner-shared SiO4 tetrahedra, and it can be seen as a structure of interconnected rings (Si-O)n of various size, denoted nMR (n-membered ring). Molecular dynamics simulations show that small-sized silica rings get a preferential orientation during the drawing, either during the high-temperature stage for 3MR, or during the cooling for 4MR and 5MR, and they persist in this state in the fiber at ambient temperature. This leads to a structural anisotropy, more specifically a “transverse isotropy”, because of different longitudinal and transversal physical properties. This anisotropic structural rearrangement during the drawing process induces a non-Newtonian behavior of the modeled glass melt, with strain-rate dependent properties.