Evaporation of Droplets on Porous Substrates #

David Craig, Stephen Wilson, Alexander Wray

11:10 Wednesday in 3Q16.

Part of the Evaporation session.

Abstract #

Both evaporation and imbibition phenomena play vital roles in a variety of industrial applications, such as micro-fabrication, pharmaceutical coatings, inkjet printing, and paintwork restoration. However, the majority of the previous research has focused on the evaporation of droplets on solid (i.e. non-porous) substrates. Analytical models, based on lubrication theory, are developed for the evolution of a liquid droplet subject to evaporation and imbibition simultaneously. Specifically, the evolution of a thin droplet situated on an initially dry or an initially flooded horizontal porous substrate is analysed. The evaporation from the droplet is driven by the diffusion of liquid molecules into the passive atmosphere. In contrast, the imbibition from the base of the droplet is driven by the pressure gradient within the porous substrate. We analyse the evolution, and hence the lifetime, in a variety of modes, specifically the constant angle, constant radius, stick-slide, and stick-jump modes. The combined effects of both evaporation and imbibition lead to a decrease in the lifetime when compared to the lifetime for droplet evaporation on a solid substrate. Additionally, the coffee-ring dynamics of a thin droplet undergoing simultaneous evaporation and imbibition will be investigated.