Thin-sheet creation and threshold pressures in drop splashing

TL;DR

This paper investigates how ambient gas properties influence the formation of a thin liquid sheet during drop impact, revealing different creation timings and a threshold velocity that suppresses splashing.

Contribution

It uncovers the dependence of thin-sheet creation timing on impact conditions and introduces a new threshold velocity that controls splashing suppression.

Findings

Thin-sheet creation timing varies with impact velocity and air pressure.

A new threshold velocity limits the formation of the thin sheet.

Lower ambient pressure suppresses splashing by affecting sheet formation.

Abstract

A liquid drop impacting a smooth solid substrate splashes by emitting a thin liquid sheet from near the contact line of the spreading liquid. This sheet is lifted from the substrate and ultimately breaks apart. Surprisingly, the splash is caused by the ambient gas, whose properties dictate when and if the sheet is created. Here I focus on two aspects of this process. Using high-speed imaging I find that the time of thin-sheet creation displays a different quantitative dependence on air pressure if the sheet is created during the early stages of spreading, rather than when the liquid has already spread to a large radius. This result sheds light on previously observed impact velocity regimes. Additionally, by measuring impacts of drops on surfaces comprised of both rough and smooth regions, I identify a new threshold velocity that limits the times at which the thin sheet can be created. This velocity determines the threshold pressure below which splashing is suppressed.