Ultrafast Interference Imaging of Air in Splashing Dynamics

TL;DR

This study uses ultrafast interference imaging to investigate how surrounding air influences splashing during a drop impact, revealing that splash initiation occurs at the drop edge rather than from a persistent air layer.

Contribution

It introduces high-speed interference imaging to analyze air dynamics beneath impacting drops, providing new insights into splash initiation mechanisms.

Findings

No persistent air layer before splash formation

Splash initiates at the drop edge during impact

Air pressure influences splashing behavior

Abstract

A drop impacting a solid surface with sufficient velocity will emit many small droplets creating a splash. However, splashing is completely suppressed if the surrounding gas pressure is lowered. The mechanism by which the gas affects splashing remains unknown. We use high-speed interference imaging to measure the air beneath all regions of a spreading viscous drop as well as optical absorption to measure the drop thickness. Although an initial air bubble is created on impact, no significant air layer persists until the time a splash is created. This suggests that splashing in our experimentally accessible range of viscosities is initiated at the edge of the drop as it encroaches into the surrounding gas.