Droplet evaporation on porous fabric materials

Abstract

Droplet evaporation on porous materials is a complex dynamic that occurs with spontaneous liquid imbibition through pores by capillary action. Here, we explore water dynamics on a porous fabric substrate with in-situ observations of X-ray and optical imaging techniques. We show how spreading and wicking lead to water imbibition through a porous substrate, enhancing the wetted surface area and consequently promoting evaporation. These sequential dynamics offer a framework to understand the alterations in the evaporation due to porosity for the particular case of fabric materials and a clue of how face masks interact with respiratory droplets.

Porous Cellulose Thin Films as Sustainable and Effective Antimicrobial Surface Coatings

“…Figure a presents the gravimetric reading of a water droplet (initial volume of 5 μL) as a function of time: the water drop evaporated clearly faster (0.271 vs 0.172 mg·min –1 ) on the cellulose-coated surface than on a planar, uncoated glass substrate. The linearity of the mass loss on the planar but solid substrate (black squares and fitted line) indicates an evaporation process governed by diffusion, with the highest evaporation flux occurring at the contact line. , The evaporation rate of sessile droplets shall thus be proportional to the contact radius . The changed evaporation kinetics observed on the cellulose film (blue dots and fitted line) reflects the accelerated evaporation discussed earlier.…”

“…The evaporation process of the sessile droplets was measured using a quartz crystal microbalance (Figure b) that is highly sensitive to changes in the temporal droplet radius. , We observed that the droplet evaporating on the planar surface (without cellulose coating) initially followed a constant contact radius (CCR) regime, during which the liquid–solid contact line was pinned while the contact angle and the droplet height decreased as the evaporation continued followed by a depinning period where the contact line contracted until the evaporation was completed. In contrast, for the substrate covered by the cellulose thin film, the droplet remained evaporating in a constant contact radius mode for most of its lifetime due to the capillary-driven spreading and imbibition in the presence of the porous medium, leading to a much accelerated evaporation process . The difference in evaporation time and associated kinetics between the two MFC film samples was not noticeable and hence not included.…”

“…The linearity of the mass loss on the planar but solid substrate (black squares and fitted line) indicates an evaporation process governed by diffusion, with the highest evaporation flux occurring at the contact line. 24 , 32 The evaporation rate of sessile droplets shall thus be proportional to the contact radius. 33 The changed evaporation kinetics observed on the cellulose film (blue dots and fitted line) reflects the accelerated evaporation discussed earlier.…”

“…In contrast, for the substrate covered by the cellulose thin film, the droplet remained evaporating in a constant contact radius mode for most of its lifetime due to the capillary-driven spreading and imbibition in the presence of the porous medium, leading to a much accelerated evaporation process. 32 The difference in evaporation time and associated kinetics between the two MFC film samples was not noticeable and hence not included.…”

High density deposits of binary colloids

“…The 2D slices were processed with the visualization Amira Software (Thermo Fisher Scientific, USA) to achieve the three-dimensional volume images presented in this work. The Amira software was used for noise reduction and smoothing by applying a Median Filter to the 2D tomographic slices, the Volume Rendering function for the generation of the 3D images, and the dimensions of the pillars and colloidal deposits for analysis with built-in measurement tools 32 .…”