Apparent contact angles and time of the three phase contact formation by the bubble colliding with Teflon surfaces of different roughness
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Polish Academy of Sciences
Maria Curie-Sklodowska University
Marta Krasowska   

Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Cracow, Poland.
Publication date: 2006-01-01
Physicochem. Probl. Miner. Process. 2006;40(1):293–306
The paper presents results and analysis of influence of hydrophobic surface roughness on apparent contact angle values (equilibrium conditions) and time of the bubble attachment (dynamic conditions) to hydrophobic solid surfaces (Teflon) of different roughness. The surface roughness of Teflon plates was modified in a mechanical way using abrasive papers and/or diamond paste of different grid numbers. Measurements of contact angles were carried out by the sessile drop technique, while the time of three phase contact (TPC) formation and the bubble attachment were determined in a course of the bubble collisions with Teflon plates, using a high speed camera (1182 Hz). It was found that the surface roughness is an important parameter affecting both quantities determined. With increasing surface roughness the static contact angle was increasing, while the time needed for TPC formation and the bubble attachment was significantly shortened, from ca. 80 to 3 ms. Air entrapped inside surface scratches seems to be a reason of these effects. With increasing roughness a larger amount of air can be entrapped inside the scratches. This hypothesis is confirmed by measurements of the diameters of contact perimeter of the attached bubble, where it was found that the perimeter increases with the surface roughness.