A Study of the Evaporation of Hexane Lenses on an Ionic Liquid Surface: Effect of Wetting Mode

The evaporation of hexane lenses on an ionic liquid (IL) (1-butyl-3-methylimidazolium hexafluorophosphate) surface is studied. The difference between the evaporation processes of the lens on the IL surface and on a distilled water (DW) surface with the same substrate liquid depth (2.6 mm) is primarily analyzed. The variation of the lens contact diameter D_C and the deformation of the IL surface were experimentally observed. The results indicated that the spreading stage of a hexane lens was notably shorter in duration on the IL surface than on the DW surface. A hexane lens was pseudopartially wetted on the DW surface, and the plane position of the lens contact diameter remained level with the water surface throughout the evaporation process. In comparison, a hexane lens was partially wetted on the IL surface, and the plane position of the lens contact diameter was lower than the horizontal surface until the lens evaporated completely. The hexane lens evaporation on the IL surface was calculated by using the diffusion-controlled evaporation model under the constant contact angle mode. The calculated results agreed well with the experimental measurements. Finally, the evaporation of hexane lenses on the DW and the IL surfaces was compared through calculations. Although the maximum lens contact diameter on the DW surface was greater, it took a longer time for the lens to evaporate on the DW surface. This is because the more significant bending of the substrate liquid surface accelerated the lens evaporation. The results of this study offer a new approach for controlling droplet evaporation.