Nonsolvent-induced phase separation synthesis of superhydrophobic coatings composed of polyvinylidene difluoride microspheres with tunable size and roughness

Polyvinylidene difluoride (PVDF) microspheres are synthesized using the non-solvent induced phase separation (NIPS) method. The diameters of the microspheres are varied from 0.3 μm to 2.8 μm by controlling the amount of water added to a solution of PVDF in dimethylformamide. Sphere aggregates are created from spun-on films whose thickness is tuned in the range 6.5-16.5 μm by varying the spin-casting rotational velocity. Spin-casting with optimized parameters results in high-surface-area films that are among the most superhydrophobic non-templated polymer coatings to date, with water contact angles up to 171°, hysteresis less than 12°, and slide angle as low as 3°. We model the dependence of sessile water contact angle on the morphological properties of the films, including not only the sphere diameter, but also nanoscale roughness of the microsphere surfaces and the geometries of macroscopic fingers formed by the aggregated spheres.