Transition in the Evaporation Kinetics of Water Microdrops on Hydrophilic Surfaces

Abstract

We describe a technique that allows measurement of the mass and shape of sessile liquid microdrops during evaporation. Therefore, the microdrops are deposited by an inkjet onto a silicon microcantilever, and the bending and the shift in resonance frequency are monitored. From hydrophobized surfaces, microscopic water drops evaporate with the same kinetics as macroscopic drops; we verify the validity of known evaporation laws to drops with diameters from 100 microm to below 10 microm. From hydrophilic surfaces, the evaporation is slowed down during the last approximately 100 ms; we believe that this occurs due to flattening of the drops, which are then stabilized by interfacial forces and disjoining pressure.

Microdroplet evaporation on superheated surfaces

“…Yet, this is surprising because reduced evaporation rates are expected for small water microdroplets in contact with a hydrophilic surface in comparison to a hydrophobic surface. For example, a transition in the evaporation kinetics due to water hydration has recently been suggested by Golovko et al [44] However, in Ref. [44], the reduction in the evaporation rate ð _ m LG Þ was observed with submicron-sized water droplets on hydrophilic Si surfaces (not micron-sized water droplets, as studied here).…”

“…That is, the droplets are still several micrometers in size (R ) d T , h ) d T ), where d T , the Tolman length, is on the order of nanometers. Therefore, the transition in _ m LG is not attributed with size-dependent deviations in the droplet's surface tension due to disjoining pressures, which are important for liquid thin-films and droplets with sizes comparable to d T [43,44]. Fig.…”

“…Moreover, in Ref. [44], the evaporation rate ð _ m LG Þ is reported (not, _ p LG , the evaporation rate per unit length of contact line, as studied here). Thus, our results are limited to micron-sized water droplets (i.e.…”

Structure of Aqueous Water Films on Textured −OH-Terminated Self-Assembled Monolayers

“…This is achieved via varying hydrogen-bonding structures to balance the demands of surface tension, hydrogen bonding, van der Waals, and other microscopic forces. 52,53 Our results point to a general conclusion that the residual D 2 O layer structures cannot be assumed to display an intuitive trend with contact angles in all systems; rather, the hydrogen-bonding network in interfacial aqueous environments varies depending on the water …”

Elastic deformation of soft membrane with finite thickness induced by a sessile liquid droplet

“…During the latest years, Bonaccurso et al have made some studies on the transverse effect of a sessile droplet on the bending of a flexible microcantilever [36][37][38][39]. Recently, they studied the surface deformation of several tens micrometers-thick PDMS membrane with very low modulus induced by a sessile droplet using laser scanning confocal microscopy and estimated that the breadth of surface layer is approximately 16.0 nm by comparison between their experimental data and Rusanov's theoretical solution [17].…”