Recoil Cavity Formation and Collapse for Drop Impact on Sieves.

The principle underpinning most printing technologies rely on is the formation and subsequent collapse of cavities to generate high-speed jets or droplets. Traditional methods, such as the Worthington jet or bubble-based cavity, utilize the collapse mechanism to give rise to a high-speed liquid jet. In contrast to known cavity collapse processes, a distinct phenomenon occurring during droplet impact on a superhydrophobic sieve is reported. Herein, the collapse of the impact cavity causes an air jet to rise through the sieve pore to form a "recoil cavity." Subsequently, the recoil cavity collapses to eject a jet (droplets). The notable discovery is the emergence of the recoil cavity as a result of the impact cavity's collapse, which has been absent on any other surfaces. The present research explores the underlying mechanism and develops a model of the phenomenon. It is found that the process follows the principle of energy conservation, with a threshold energy flux ratio between impact and recoil driving the ejection of a single drop. These findings provide valuable insights for understanding drop impact printing techniques, which can be applied across various fields, including electronics, biology, and structural printing.