Marangoni-driven flow instability accelerates liquid-solid contact on atomically smooth mica

TL;DR

This study reveals that Marangoni-driven flow instability on alcohol droplets in humid air causes uneven surface patterns, which accelerate contact with atomically smooth mica surfaces, and shows how altering liquid composition can suppress this instability.

Contribution

It uncovers the role of Marangoni instability in accelerating contact on smooth surfaces and demonstrates how to control this process by changing liquid composition.

Findings

Surface patterns due to instability accelerate contact.

Varying liquid composition suppresses instability.

Characterized growth rate and length scale of patterns.

Abstract

A droplet falling toward a solid surface displaces the surrounding air until it encounters a defect, and contact nucleates. On atomically smooth surfaces devoid of defects, contact can be delayed until the droplet rebounds; however, above a critical impact velocity the droplet always contacts the surface. Here we show that for alcohol droplets in a humid atmosphere, the surface of the droplet above the solid develops patterns as a consequence of an instability; consequently, the liquid approaches the surface more closely in some places than others, accelerating contact formation. We demonstrate the attenuation and even suppression of this instability by varying the liquid composition, and characterize the growth rate and length scale of the patterns on liquid-air interface.