Non-Fluorinated, Superhydrophobic Binder-Filler Coatings on Smooth Surfaces: Controlled Phase Separation of Particles to Enhance Mechanical Durability.

There has been a recent drive to develop non-fluorinated superhydrophobic coatings due to the toxicity, cost, and environmental impact of perfluorinated components. One of the main challenges in developing superhydrophobic coatings in general and non-fluorinated superhydrophobic coatings in particular is optimization of mechanical durability, as the rough asperities required for maintaining superhydrophobicity tend to be easily removed by abrasion. Although rough and self-similar hydrophobic surfaces composed of loosely adhered particles or highly porous structures tend to produce excellent superhydrophobicity, they have low inherent mechanical durability and their longevity under real conditions is compromised. To address this issue, this work investigates the addition of a polymeric matrix material (the binder) to hydrophobic nanoparticles (the filler) to produce spray-coated superhydrophobic surfaces with improved inherent mechanical durability. Hansen solubility parameters were used to tune the interactions between the binder, filler, and solvent used to deliver the coating. It was found that lowering the binder/filler miscibility and using a poor solvent mixture generates more surface roughness, thereby lowering the minimum filler load required to achieve superhydrophobicity. This leads to an overall more inherently durable system that remains hydrophobic for thousands of light abrasion cycles.