Hydroxylation and water-surface interaction for S-glass and silica glass using ReaxFF based molecular dynamics simulations

Hydrolysis at the water-glass interface significantly influences glass surface reactivity and adhesion characteristics. In glass fiber reinforced epoxy composite interphases, hydroxyls on the glass fiber surface reacts with silane coupling agents to form covalent bonds between the fiber and polymer matrix. In this study, the surface reactivity and hydrolysis reaction of silica glass and S-glass (Mg aluminosilicate glass with 65 % SiO2, 25 % Al2O3, and 10 % MgO in weight ratio) are simulated using ReaxFF molecular dynamics (MD) to investigate the formation of surface defects (i.e., under-coordinated atoms) and hydroxyls (number density, types and spatial distribution) at four surface annealing temperature conditions (300 K, 700 K, 1000 K and 1300 K). Our study showed that a higher areal number density of surface defects and hydroxyls formation occur at lower surface annealing temperature conditions. S-glass was predicted to have a lower number density of hydroxyls compared to pure silica glass. In addition, analysis on hydroxyl oxygen revealed the defects and oxide bond connected to Mg are responsible for hydrolysis in S-glass. RDF and hydroxyl categorization analysis revealed the S-glass could have closer proximity among hydroxyls despite the lower hydroxyl areal number density than silica glass. Lastly, silica glass showed more physisorbed water and surface energy, which agrees with previous studies. This surface hydrolysis and reactivity analysis study will guide the experiments to control the fiber coating process to tailor interphase in glass fiber-epoxy composites.