Vapor Nucleation\non Hybrid-Wetting Nanoconvex Surfaces:\nThe Competition between Intrinsic Wettability and Topography

Hybrid-wetting surfaces with hydrophilic\nspots reduced\nfrom the\nmicrometer to nanometer scale have been confirmed to enhance vapor\nnucleation while simultaneously minimizing droplet pinning. Given\nthat surface topography also plays a critical role in influencing\nnucleation characteristics, the effect of competition between intrinsic\nwettability and topography on nucleation remains unclear when both\nsurface topography and hydrophilic regions approach the critical nucleation\nsize. This work investigated vapor nucleation on two types of hybrid-wetting\nnanoconvex surfaces. On random hybrid-wetting convex surfaces, the\nmost negative potential energy sites were located at the sides of\nthe convex structures, leading vapor to preferentially nucleate at\nthese locations, consistent with observations on homogeneous surfaces.\nDespite similar average potential energy values across the surface,\nwettability variations in hydrophilic and hydrophobic atoms significantly\nalter the surface energy distribution. As the wettability difference\nbetween hydrophilic and hydrophobic atoms increases, stronger hydrophilic\natoms generate relatively higher local energy regions, promoting vapor\nrapid nucleation. The edge effect still exists at a hydrophilic atom\nratio of 10%, and competition among hydrophilic spots impedes vapor\nnucleation and growth. However, when the ratio increases to 40%, the\nincreased surface average potential energy promotes the probability\nof vapor contacting the surface, leading to rapid vapor nucleation\non the sides of the convex structures. In addition, surface potential\nenergy analysis and the Monte Carlo method revealed that nucleation\nlocations on nanoconvex surfaces are governed by the competition between\nintrinsic wettability and topography. When the magnitude of the potential\nenergy generated by the hydrophilic atoms exceeds that from the topography,\nstronger solid–liquid interactions at the top of the convex\nstructure increase the likelihood of vapor contacting the surface,\nresulting in nucleation at the top. Conversely, when the magnitude\nof the potential energy generated by hydrophilic atoms is lower than\nthat from topography, nucleation preferentially still occurs on the\nsides.