Evaporation of Droplets of Surfactant Solutions

Abstract

The simultaneous spreading and evaporation of droplets of aqueous trisiloxane (superspreader) solutions onto a hydrophobic substrate has been studied both experimentally, using a video-microscopy technique, and theoretically. The experiments have been carried out over a wide range of surfactant concentration, temperature and relative humidity. Similar to pure liquids, four different stages have been observed: the initial one corresponds to spreading till the contact angle, θ, reaches the value of the static advancing contact angle, θad. Duration of this stage is rather short and the evaporation during this stage can be neglected. The evaporation is essential during next three stages.The next stage after the spreading, which is referred to below as the first stage, takes place at constant perimeter and ends when θ reaches the static receding contact angle, θr. During the next, second stage, the perimeter decreases at constant contact angle θ=θr for surfactant concentration above critical wetting concentration (CWC). The static receding contact angle decreases during the second stage for concentrations below CWC because the concentration increases due to the evaporation. During the final stage both the perimeter and the contact angle decrease till the drop disappears. Below we consider only the longest stages one and two.The developed theory predicts universal curves for the contact angle dependency on time during the first stage, and for the droplet perimeter on time during the second stage. A very good agreement between theory and experimental data has been found for the first stage of evaporation, and for the second stage for concentrations above CWC, however, some deviations were found for concentrations below CWC.3

Smart and green interfaces: From single bubbles/drops to industrial environmental and biomedical applications

“…The theory developed for pure liquids is applicable also to nanofluids [54], where a good agreement with the available experimental data has been found. However, in the case of evaporation of surfactant solutions the process deviates from the theory predictions for pure liquids at concentration below critical wetting concentration and is in agreement with the theory predictions at concentrations above it [52,53]. It was found that evaporation for microdroplets is considerably different as compared with macrodroplets: These deviations are caused by an increasing influence of the kinetic effects at the liquid-gas interface (Hertz-Knudsen-Langmuir equation) and this theory should be applied together with the diffusion equation of vapor in the air if the droplet size is less than 1 µm.…”

“…Recently a considerable progress in theoretical and experimental studies of simultaneous spreading and evaporation of liquid droplets on solid substrates has been achieved [47,48,49,50,51,52,53,54] in the case of both complete wetting [47] and partial wetting [48,49,50,51]. A universal behavior has been predicted and experimentally verified for both cases.…”

Evaporation of Sessile Droplets Laden with Particles and Insoluble Surfactants

“…[21][22][23][24][25][26][27] More specifically, Still et al 22 achieved a uniform deposition of colloidal particles on glass by adding Sodium dodecyl sulfate (SDS) to the drop dispersion.…”

Steady-state droplet evaporation: Contact angle influence on the evaporation efficiency

“…In practical situations, thermo-fluid properties are modified by unwanted contaminants (e.g., pump oils in fluid refrigerants) and/or irreversible reactions/processes. The fluid properties are also engineered to (i) overcome such bottlenecks or (ii) extend the application space of a given base-fluid, where surfactants [51], corrosion inhibitors [52], bio-molecules [53], and colloidal particles [54][55][56][57] are commonly used additives. Surfactant and colloidal loadings typically reduce the overall evaporation rate, magnitude of convective flows, and depinning dynamics; yet, such additives can also result in shear-thinning phenomena [10,58], flow inversion [59], and suppression of the coffee-ring effect [60] if loadings of anisotropic geometries are used [61].…”