Maximal air bubble entrainment at liquid drop impact

TL;DR

This study investigates the conditions under which a liquid drop impact on a solid surface entrains the maximum air bubble size, revealing an optimal impact velocity and droplet size that maximize entrapment.

Contribution

The paper combines experimental, theoretical, and numerical methods to identify the impact conditions that lead to maximal air bubble entrapment during drop impact.

Findings

Maximum air bubble size occurs at an optimal impact velocity and droplet size.

Inertia and capillary forces compete to minimize entrapped bubble size.

Results are relevant for applications in printing, microelectronics, and agriculture.

Abstract

At impact of a liquid drop on a solid surface an air bubble can be entrapped. Here we show that two competing effects minimize the (relative) size of this entrained air bubble: For large drop impact velocity and large droplets the inertia of the liquid flattens the entrained bubble, whereas for small impact velocity and small droplets capillary forces minimize the entrained bubble. However, we demonstrate experimentally, theoretically, and numerically that in between there is an optimum, leading to maximal air bubble entrapment. Our results have a strong bearing on various applications in printing technology, microelectronics, immersion lithography, diagnostics, or agriculture.