Spray-Coated Fluorine-Free Superhydrophobic Coatings with Easy Repairability and Applicability

The present paper reports a very simple and low-cost fluorine-free superhydrophobic coating prepared by spray-coating metal alkylcarboxylates, for example, Cu[CH₃(CH₂)₁₀COO]₂, onto virtually any substrates. Superhydrophobicity with a static water contact angle of about 160° and a sliding angle of 5° was achieved from the proper precursor concentration. The advantages of the present approach include the cheap and fluorine-free raw materials, environmentally benign solvents, an industrial implementation method, and easy repairability and applicability so as to make a great application potential in practice. The hydrophobicity of coatings and the adhesion to water were found to be dependent on the surface morphology that was governed by the precursor concentrations from which coatings were prepared. The static wetting behavior of water droplets with different sizes gentlly deposited on the coatings was studied in more detail and correlated to theories, i.e., Wenzel’s and Cassie’s models. The results indicated that nanoribbon-textured coatings prepared from low precursor concentration (0.02 M) exhibited a transition from the metastable Cassie−Baxter state to the Wenzel state with increments in the droplet volume, and eventually droplets firmly stick to the surface even when the droplet was gently deposited on the surface. Surface coatings with dual roughness at both microscale and nanometer scale were formed as the concentration (0.04 M) was increased and conferred a stable Cassie state, even for increased droplet size and increased droplet deposit speed.