Super-enhanced evaporation of droplets from porous coatings

Hypothesis: The addition of a thin, hydrophilic, porous, coating to an impermeable solid will lead to more rapid evaporation of liquid droplets that impinge on the solid. The droplet will imbibe quickly, but the progress normal to the interface will be limited to the thickness of the coating, and therefore the liquid will spread laterally into a broad disk to expose a large liquid-vapor interface for evaporation. Experiments: Liquid droplets of volume 2.5-25 lL were placed on solids and then both the mass and area of each droplet were monitored over time. We compared data for smooth, impermeable hydrophilic glass to the same glass that was coated in thin (35-109 lm) porous, hydrophilic-glass layer fabricated from glass beads. Findings: The droplet was imbibed (wicked) into the coating within seconds, and the liquid spread later-ally to form a thin, broad, disk. Critically, evaporation of a droplet was enhanced by a factor of 7-8 on the thin coating. The evaporation rate was not proportional to the reciprocal thickness of the coating. The ability to enhance evaporation of small droplets on a solid may have practical applications, for example, in speeding the death of microbes. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

The addition of a thin, porous, hydrophilic coating to an impermeable solid can accelerate the evaporation of liquid droplets. The droplets are quickly absorbed and spread laterally to form a thin, broad disk, which increases the liquid-vapor interface for evaporation. Experimental results show that the evaporation rate of droplets on the thin coating is enhanced by a factor of 7-8, and it is not proportional to the reciprocal thickness of the coating. Enhancing the evaporation of small droplets on a solid surface can have practical applications, such as expediting the death of microbes.