Criteria for antibubble formation from drop pairs impinging on a free surface

An antibubble, the counterpart of an ordinary bubble, consists of a liquid drop separated from the bulk liquid by a thin film of gas, where understanding of its formation mechanism remains limited. Four criteria are reported for antibubble formation by drop pairs impinging on a free surface based on scaling analysis and experimental characterization. This work not only elucidates the underlying formation physics of antibubbles, but it also provides useful guidelines to control antibubble generation.