Dynamics of bubble formation on superhydrophobic surface at quasi-static regime

We experimentally studied bubble formation on superhydrophobic surface (SHS) under a constant gas flow rate and at quasi-static regime. The radius of SHS R_SHS varied from 4.2 mm to 19.0 mm, and the gas flow rate varied from 1 to 150 ml/min. We measured the bubble volume, bubble geometrical parameters, contact angle, as well as forces acting on the bubble. We found that as increasing R_SHS, the bubble switched from Mode A where the bubble base pinned at the rim of SHS to Mode B where the contact line didn’t reach to the SHS boundary. Moreover, we found that Q had minor impacts on bubble shape but caused an increase of the bubble detached volume. After proper normalization, the relationship between V_d and Q agreed with these for bubbles detaching from hydrophilic and hydrophobic surfaces. During the necking process, the necking radius followed a similar power-law relation to that for a bubble necking at a nozzle, and the bubble volume was nearly a constant for small Q but increased significantly at large Q. Last, we found that the bubble growth is governed by a balance between one lifting force (pressure force) and two retaining forces (surface tension force and buoyancy force).