Geostructure-Induced Nonmonotonic Transition between Cassie and Wenzel States on Hydrophilic Substrates

Water-mediated weathering drives the deterioration of carbonate-cemented sandstone heritage, yet the interplay between surface roughness and wettability on intrinsically hydrophilic carbonates remains obscured by experimental constraints. Herein, molecular dynamics simulations are employed to elucidate nanodroplet wetting on hydrophilic surfaces (baseline smooth-surface contact angles of ∼72° and ∼85°). This design diverges from conventional topological scaling. It maintains a constant groove width while densifying the pillars. This configuration reveals a nonmonotonic transition sequence: Wenzel → Cassie → Wenzel → Cassie. Mechanistically, this oscillation arises from discrete jumps in the number of pillars spanned by the droplet base. These jumps force the contact line to elongate and modulate the local curvature at the droplet base, which in turn triggers a reversion to the Wenzel state. Furthermore, we demonstrate that this complex effect is strictly confined by physicochemical boundaries: enhanced hydrophilicity (∼72°) significantly suppresses the transition window compared to the ∼85° surface, with smaller droplets exhibiting heightened sensitivity. These findings link discrete geometric variations to nonmonotonic wetting-state variations, offering a theoretical reference for understanding wettability evolution during carbonate weathering.