Effect of roughness on wettability and floatability:Based on wetting film drainage between bubbles and solid surfaces

Wetting film thinning measurement was introduced to clarify the wettability and floatability of solid surfaces with varying roughness. The wettability was quantified using the contact angle measurement combined with the dynamic force microbalance test between solid surfaces and water droplets, while the floatability was investigated by the bubble-solid surface dynamic attachment observation and the induction time measurement. The results show that the water contact angles reduce(14.53°, 12.74°, and 6.71°)with the increase of glass surface roughness, while the water droplet-glass adhesion forces intensify(11.1, 19.1 and 19.2 μN) owing to the stable wetting film. The distortion of the contact surface and the Wenzel state are the causes. In contrast, the hydrophobized surfaces have the growing apparent contact angles(38.08°, 69.81°, and 81.01°), declining adhesion strength and shortening induction time(863, 352and 12 ms) along with the increasing surface roughness. The weak wettability and fine floatability on the rough hydrophobized surface is reflected in the fast wetting film drainage dynamics and three-phase contact formation, which may be attributed to the wetting film with short diameter on tiny rough nubs and the entrapped air in the grooves as a bridge between the bulk bubble and the solid surface.