Nanopore-Mediated Spontaneous Dilution of Droplets: When Evaporation Turns to a Dilutor

Abstract

Droplet evaporation on surfaces is ubiquitous and affects areas as diverse as climate, microbiology, the chemical industry, and materials science. While solute concentration is the universally taken-for-granted behavior in drop evaporation, the present work shows that saline droplets evaporating on nanoporous thin-film surfaces can get diluted rather than concentrated. The driving mechanism of this phenomenon is attributed to the flow drawn from the drop through the nanopores by an annular peripheral evaporation. This fluid transport can continuously collect the salt solution from a concentrated region of the droplet, which is induced by radial microflows during drop evaporation. The coupling of these processes leads to the overall drop dilution effect. The influence of substrate temperature and drop volume was also investigated. This study opens up new perspectives on many natural phenomena and offers alternatives for physicochemical applications in small dimensions as well as for water desalination technologies.

Pushing the limits of nanopore transport performance by polymer functionalization

“…126 Another recent example of using this correlation is the observation that water droplets on porous surfaces dilute upon evaporation. 127…”

“…126 Another recent example of using this correlation is the observation that water droplets on porous surfaces dilute upon evaporation. 127 In addition to electrostatic interactions and wettability, ligand binding or specific interactions with functional groups at the nanopore wall strongly influence the molecular passage or adsorption of dissolved molecules through the nanopore.…”

Virtual Issue on Multifunctional Nanoporous Materials in Latin America

“…18 Unusual nanofluidic effects have been found due to dynamic processes taking place in salt solutions confined within mesoporous thin films. 19,20 Open macroporous structures facilitate interactions between electroactive species and catalytic sites, permitting novel electrodes for Zn−air batteries. 21 Surface functionalization of mesoporous silica nanoparticles is critical for biomedical treatments, either for colloidal stability and dispersibility, 22 or for improved immobilization of functional enzymes.…”

“…The importance of understanding molecules under confinement is illustrated by recent findings where transport, sorption, and size-selective catalytic properties of aluminosilicates such as ZSM-5 and its low-crystallinity precursors are critically dependent on pore size and connectivity which, in turn, can be kinetically controlled through synthesis . Unusual nanofluidic effects have been found due to dynamic processes taking place in salt solutions confined within mesoporous thin films. , Open macroporous structures facilitate interactions between electroactive species and catalytic sites, permitting novel electrodes for Zn–air batteries …”