Direct measurements of air layer profiles under impacting droplets using high-speed color interferometry

TL;DR

This study employs high-speed color interferometry to directly measure the air layer profile beneath impacting droplets, providing insights into the early wetting dynamics and air escape during droplet impact.

Contribution

It introduces a novel method for real-time measurement of the air layer profile under impacting droplets, enhancing understanding of impact dynamics and wetting mechanisms.

Findings

Measured air layer thickness before and during impact.

Quantified air exit velocity from the gap.

Analyzed wetting mechanism and bubble entrapment.

Abstract

A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process. Based on the time evolution of the extracted profiles obtained at multiple times, we measure the velocity of air exiting from the gap between the liquid and the solid, and account for the wetting mechanism and bubble entrapment. The present work offers a tool to accurately measure the air layer profile and quantitatively study the impact dynamics at a short time scale before impact.