Waxing the soot: Practical fabrication of all-organic superhydrophobic coatings from candle soot and carnauba wax

Abstract

Commercial application of superhydrophobic coatings is hindered by insufficient durability and use of materials with high costs and limited availability. In this study, we report a robust water impact resistant all-organic superhydrophobic coating that is prepared from low-cost colloidal dispersion composed of carnauba wax and candle soot. The colloidal dispersion is stable and can be spray-coated onto virtually any surfaces. The coated surfaces exhibit superhydrophobicity with a water contact angle of 172° and sliding angle of 3°, and retain superhydrophobicity even after 400 cycles of continuous water spray with an impact pressure of 7.4 kPa. The synergetic combination of candle soot and carnauba wax, together with the deposition method, solvent used to disperse materials, and spray-coating distance are critically important for the superhydrophobicity and mechanical durability. The robustness of the coatings emerges from the two-tier hierarchical structure of the dried particles which is formed by evaporation induced self-assembly of wax molecules and candle soot nanoparticles. Applications in self-cleaning and oil/water separation are demonstrated, where a coated membrane can be continuously operated, solely driven by gravity, and can separate common organic liquids such as hexane and toluene from water with a separation efficiency of more than 90 % at a high flux of 1061 L / (m2 h).