Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Uncertainty and Irreproducibility of Triboelectricity Based on Interface Mechanochemistry

Triboelectrification mechanism is still not understood, despite centuries of investigations. Here, we propose a model showing that mechanochemistry is key to elucidate triboelectrification fundamental properties. Studying contact between gold and silicate glasses, we observe that the experimental triboelectric output is subject to large variations and polarity inversions. First principles analysis shows that electronic transfer is activated by mechanochemistry and the tribopolarity is determined by the termination exposed to contact, depending on the material composition, which can result in different charging at the macroscale. The electron transfer mechanism is driven by the interface barrier dynamics, regulated by mechanical forces. The model provides a unified framework to explain several experimental observations, including the systematic variations in the triboelectric output and the mixed positive-negative "mosaic" charging patterns, and paves the way to the theoretical prediction of the triboelectric properties.

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.