Ionic liquid-controlled evaporation kinetics of an aqueous sessile drop

Evaporation of a water droplet is well understood from the view of molecular diffusion. Even though there are reports that discuss the effects of inorganic salts, the evaporation of a water droplet with added organic salts, such as ionic liquids, is rare. In the present study, ionic liquids controlled simultaneous spreading and evaporation of a water droplet have been studied using video microscopy techniques. In the presence of these molecules, the sessile drop starts to evaporate in a constant contact radius (CCR) mode, due to the pinning of the triple-phase contact line to a hydrophobic substrate. Later, it shifts to constant contact angle (CCA) mode for a short while, which finally enters a contact angle recovery mode after reaching to a minimal. The presence of these molecules in water ultimately enhances the evaporation rate by assembling themselves at the water–air interface. Such assembly reduces the interfacial tension enhancing the probability of escaping the water molecule from liquid to gas phase. The variation of volume with time has been fitted using a model equation which indicates the increased value of diffusion coefficient. Additionally, the experiments with varying relative humidity show that the contact angle recovery is prominent in a humid environment. The molecular dynamic simulation has been performed to finally calculate the solvation free energy of the system, which ensures the ionic liquids to assemble at the interface. This assembly plays a vital role in evaporation kinetics. © 2024