Surface wettability of poly(vinylidene fluoride) nanoparticle assembly surfaces

Poly(vinylidene fluoride) (PVDF) is one of the most extensively used polymers for superhydrophobic coatings because of its low surface free energy and inertness to various chemicals. Based on general rules, not only a low surface free energy but also high surface roughness is required for preparing artificial superhydrophobic surfaces. Therefore, enhancement of the hydrophobicity of PVDF coatings is commonly conducted through a two-stage method: incorporation of micro/nanoparticles into the PVDF matrix and postcoating with low-surface-energy materials. In our previous work, a nonsolvent-induced crystallization method was applied to obtain PVDF nanostructure assemblies with different surface morphologies through the selection of various nonsolvents. In this work, we investigated how morphologies influenced the surface wettability of PVDF nanostructure assembly coatings. The coatings consisting of nanoparticles exhibited highly improved hydrophobicity compared with that of the flat drop-coating PVDF surface. As the portion of nanoparticles increased, the roughness of the surfaces increased, as did the water contact angle (WCA). In the case of surfaces composed of nanoparticles (60-250 nm in diameter), superhydrophobic and oleophilic properties were achieved with a high air-pocket fraction, as described by the Cassie-Baxter model. These results provide valuable insight into PVDF surface design, especially for superhydrophobic coatings.