Molecular dynamics study of sulfuric acid droplet wetting on the calcium-silicate-hydrate substrate

The wettability of calcium-silicate-hydrate (C-S-H) surfaces plays a critical role in the performance and durability of cementitious materials, particularly in chemically aggressive environments such as those affected by acid rain. Despite the significance of sulfuric acid in degrading concrete, the molecular-level mechanisms underlying its interaction with C-S-H surfaces remain poorly understood. In this study, molecular dynamics simulations were employed to investigate the dynamic wetting behavior of sulfuric acid droplets with varying concentrations (0-16 wt%) on C-S-H substrates. The results reveal a concentration-dependent increase in equilibrium contact angles, highlighting the role of sulfuric acid in enhancing droplet cohesion and reducing wettability. This behavior contrasts with the well-documented trend for neutral salt solutions, such as NaCl, where increasing concentration reduces contact angles and enhances hydrophilicity. Radial distribution function (RDF) analyses show distinct hydration shell structuring and clustering at higher concentrations, while mean square displacement (MSD) profiles indicate reduced molecular mobility. These findings provide new insights into the unique molecular interactions of sulfuric acid with C-S-H surfaces, offering a molecular framework to mitigate degradation and improve the resilience of cementitious materials under acidic conditions. This work fundamentally advances the field by elucidating the distinct wetting behavior of sulfuric acid, which has not been previously explored, and by providing a foundation for understanding acid-induced modifications to C-S-H wettability.