Effect of surface metrology on the wettability of SiO2 nanoparticle coating

In this work, we fabricated an array of model hydrophobic surfaces with controlled roughness to establish a correlation between surface structure and observed hydrophobicity. SiO₂ nanoparticles of different sizes (7, 12, 14 and 40 nm) were layer-by-layer spin-coated on glass supports to study the effect of surface roughness on wettability evaluated by water contact angles. The hydrophobicity of one-layer structured surfaces improved with an increase in particle size. Deposition of bigger nanoparticles on top of smaller ones, generating double-layer structures, resulted in rougher surfaces with higher hydrophobicity. A strong correlation between the size ratio of deposited nanoparticle combinations and roughness was observed. Based on these correlations, it is now possible to tune surface roughness and subsequent wettability by controlling the sizes of the nanoparticle layers.