Facile preparation of a mechanically robust superhydrophobic acrylic polyurethane coating

A superhydrophobic (SH) surface is usually constituted by a combination of low surface energy substances and micro- and nanometer scale roughness structures. The latter, however, always have poor mechanical strength and require complicated fabrication procedures, seriously hindering the large-scale preparation and industrial application of SH surfaces. In this study, by introducing fluoroalkyl silane modified silica nanoparticles into hydroxyl acrylic resin using a simple spray-coating method, an SH acrylic polyurethane (SAPU) coating with good abrasion resistance and stable adhesion was obtained after cross-linking with polyisocyanate at room temperature. By virtue of the reaction between the silanol groups in silica NPs and the isocyanate groups in the curing agent, the hydrophobic silica NPs were stably anchored into the SAPU resin matrix while constructing hierarchical micro- and nanometer scale roughness structures on the coating surface. The dual characters ensure that the SAPU coating has a static water contact angle (CA) of >160°, a sliding angle of ∼10° and good mechanical properties, which exhibits CAs of >150° after wearing with sandpaper and maintains strong adhesion even after cross-cutting or impacting tests. Moreover, the SAPU coating retains an excellent water-repellent property after 12 h of immersion in hydrochloric acid with pH = 1, and can recover its water-repellent property after 12 h of immersion in sodium hydroxide solution with pH = 14 through hot air blowing. The facile spray-coating method as well as a mild room temperature curing process make this kind of SH coating especially suitable for non-wetting protection or modification of large-scale parts, providing a novel pathway for the development of a high performance SH surface.