Evaporation-Triggered Segregation of Sessile Binary Droplets

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 the phase segregation of an evaporating sessile binary droplet, consisting of a miscible mixture of water and a surfactantlike 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 nonvolatile 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.

Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops

“…If such components are surface-active, the transport processes inside the droplet can be drastically affected. That has been shown for bulk mixtures [3][4][5][6] and surfactant solutions [7][8][9].…”

Convection-dominated dissolution for single and multiple immersed sessile droplets

“…For a multi-component drop dissolving in a host liquid, there is formation of Marangoni flow caused by the variation of surface tension over the droplet surface, which in addition can influence the behaviour of emulsification (Tan et al 2019). Similarly, the Marangoni flow also plays a crucial role in multi-component sessile Convection-dominated dissolution for immersed sessile drops 892 A21-3 droplet evaporation (Scriven & Sternling 1960;Tan et al 2016;Diddens et al 2017;Kim et al 2017;Edwards et al 2018;Li et al 2018bLi et al , 2019.…”

The value of a fading tracer

“…Precipitation of sodium chloride (Soulie et al 2015) or liquid-liquid phase separation (Tan et al 2016;Li et al 2018) have been previously used to determine saturation conditions. In these cases, however, the indicating phenomenon strongly affects the fluid physics.…”

“…Another drawback is the irreversibility of particle dissolution, which would obscure non-monotonic concentration changes. Only very recently, Li et al (2018) have used the selective solubility of dyes to resolve evaporation-induced phase separation by confocal microscopy. A similar approach should be possible for a homogeneous system, using a dye with a calibrated solvatochromic shift.…”