Hierarchical assembly of nanoparticles (NPs) is of interest for omniphobic surfaces in the way that hierarchical scale roughness possibly provides effective liquid repellency and also it is relatively easy to build large-area coatings via the bottom-up assembly process. However, all NP assemblies often lacks mechanical robustness. Hence, the development of the effective fabrication method to make well-deposited hierarchical NPs assembly is demanded.
In this report, we have demonstrated an all-NP three-dimensional hierarchical surface that is omniphobic yet highly transparent and mechanically robust. By taking advantage of sublimation and recondensation of smectic A liquid crystals (LCs) in a simple thermal annealing process, we patterned NP aggregates in one-dimensional grooves directed by LCs. The resultant groove-like NP-assembled surface showed omniphobicity, repelling water, glycerol, ethylene glycol, and olive oil (with contact angle of 156.5°, 147°, 136.5°, and 123.2°, respectively) because of the low surface energy of the fluorinated NPs and dual roughness. The coating is highly transparent with ∼90% transmittance in the visible wavelength. We investigate the mechanical robustness of the all NP coatings by sand abrasion, which shows nearly identical omniphobicity and transparency after the sand abrasion.