HANGING/PENDANT BUBBLE

Figure:2.14 Pendant bubble

Figure:2.15. Necking

For a pendant bubble

Buoyancy would pull the drop upwards and a neck (fig:2.15) would form as the difference in density increases. If volume is more than a critical limit, the bubble would detach from the surface.

This phenomenon occurs only for contact angles hydrophobic surface.

Considering the case of a pendant drop, we take b as the length scale.