Superhydrophobic surfaces with near-zero sliding angles realized from solvent relative permittivity mediated silica nanoparticle aggregation

Abstract

Multi-scale roughness from nano- to micro-scale over a large area is easily generated with a coating of colloidal silica solution in which the silica nanoparticles are aggregated in a controlled manner by the addition of organic solvents. The relative permittivity of the solvent mixture surrounding the silica nanoparticles is shown to be a key factor in the control of nanoparticle aggregation, and can lead to the formation of multi-scale roughness. The coatings are initially superhydrophilic, and become superhydrophobic after surface treatment with typical hydrophobic coupling agents such as octadecyltrichlorosilane. It is shown that there exists a critical value of the relative permittivity of the solvent medium below which coatings with extreme water repellency, along with near-zero sliding angles, are generated.