2018 Volume 13 Issue 3 Pages JFST0015
We investigate behavior of bouncing and rupturing air bubbles on solid surfaces experimentally. We focus our attention to how the hydrophilicity of the solid surface alters the rupture process. We observe motion of the single bubble of a fixed diameter on several flat glass plates using high-speed cameras. In this experiment, we use two kinds of plate whose contact angles are different from each other. The bubble rises and bounces on the glass surface several times without touching the plate. It is found that, on the weakly hydrophilic glass plate whose contact angle is 65 degree, the liquid film between the bubble and the solid surface ruptures within about a hundred milliseconds after bouncing. The rupture starts at a single site. In contrast, on a highly hydrophilic glass whose contact angle is 7.6 degree, rupture time becomes much longer, i.e. more than 30 minutes. The rupture starts at several sites simultaneously. Note that in the both cases bounce times, bounce intervals, and bounce distance, are quite similar. Quite large difference in onset of rupture indicates that the existence of surface nanobubbles on the weakly hydrophilic glass enhances the rupture of liquid film. In the case of highly hydrophilic glass, the penetration of air into the liquid film after the rupture exhibits the pattern similar to viscous fingering.