Control of impact-induced cavitation using bubble-contained PVA gel*

A liquid jet is used for inkjet printers and needleless injections. We focus on the ejection method using an impulsive force. When the concaved gas-liquid interface obtains the sudden acceleration, the interface forms a focused jet. It was found that the strong impact induces cavitation bubbles which accelerate the jet (Kiyama et al., J. Fluid Mech. 2016). However, it is difficult to control the number/size of the bubbles, which is strongly related to the jet speed. In this study, we control cavitation-induced acceleration of the jet by utilizing a PVA gel which initially contains tiny bubbles. We submerge the gel in a liquid container and add the impact to the container. Remarkably, the jet speed can be controlled by the initial size/number of bubbles in the gel, which is easily controlled. Furthermore, we find that the cavitation bubbles in a liquid is suppressed by introducing the gel. To reveal the mechanism, we measure the pressure fluctuation in the liquid using a hydrophone. We find that the pressure after the impact is attenuated significantly. It indicates that the bubbles in the gel cause the attenuation, which enhances the jet acceleration.