Evaporation-triggered segregation of sessile binary droplets

TL;DR

This study investigates how phase segregation in evaporating binary droplets of water and 1,2-hexanediol affects evaporation dynamics, revealing that segregation reduces evaporation rate and halts it due to shielding effects.

Contribution

It provides new insights into the evaporation-triggered phase segregation process in binary droplets and its impact on evaporation behavior.

Findings

Segregation reduces water evaporation rate.

Evaporation halts due to shielding by 1,2-hexanediol.

Flow dynamics are driven by Marangoni effects.

Abstract

Droplet evaporation of multicomponent droplets is essential for various physiochemical applications, e.g. in inkjet printing, spray cooling and microfabrication. In this work, we observe and study phase segregation of an evaporating sessile binary droplet, consisting of a mixture of water and a surfactant-like liquid (1,2-hexanediol). The phase segregation (i.e., demixing) leads to a reduced water evaporation rate of the droplet and eventually the evaporation process ceases due to shielding of the water by the non-volatile 1,2-hexanediol. Visualizations of the flow field by particle image velocimetry and numerical simulations reveal that the timescale of water evaporation at the droplet rim is faster than that of the Marangoni flow, which originates from the surface tension difference between water and 1,2-hexanediol, eventually leading to segregation.