Durability and restoring of superhydrophobic properties in silica-based coatings.

The durability and restorable properties of superhydrophobicity are a most important issue essential for utilization of superhydrophobic materials in industrial and domestic fields. In this work, we have focused on the sol-gel dip coating synthesis, durability, and restoring properties of a superhydrophobic surface composed of spherical silica particles with low energy free surface successfully achieved on the surface of glass substrates. The water contact angle (WCA) of the as-prepared superhydrophobic coatings reached as high as 170±1° (WCA=170±1°) and the sliding angle was 3±1° (WSA=3±1°). The behavior of wettability on superhydrophobic coating surface under various external disturbances including outdoor environments, heat, and mild acidic condition is investigated. It is shown in particular that degradation and repairing of surface methyl groups between two such surfaces leads to a fully restorable coating surface by the surface modification with trimethylchlorosilane (TMCS) at room temperature. The coating also holds good thermal stability; it holds superhydrophobicity up to 550 °C and gets degrade into superhydrophilicity above 600 °C without deforming surface morphology. The results confirm the durability of the silica coating under different external disturbances and sol-gel dip coating method and restoring property provide the best solution to fabricate superhydrophobic silica coating surface with extended durability at low cost.