A07 Is surface tension reduced by ultrafine bubbles (cavitation nuclei)?

Abstract

It has been experimentally reported that surface tension is reduced by the presence of ultrafine bubbles (bulk nanobubbles) by about 14 % [A.Ushida et al., J.Surfact.Deterg. 15, 695 (2012)]. In the experiment of Ushida et al., surface tension was measured by the liquid height from a ring to the liquid surface when the liquid film ruptures using the du Nouy ring method. According to the dynamic equilibrium model, an ultrafine bubble is stabilized by partly covered with hydrophobic impurities. In the present study, it is theoretically shown that ultrafine bubbles are concentrated at the liquid surface due to the hydrophobic impurities partly covering the bubbles. It is suggested that rupture of liquid film is accelerated by the presence of the bubbles at the liquid surface. It may be the reason for the reduction of surface tension by the presence of ultrafine bubbles in the du Nouy ring method.