Evaporation of Nanosuspensions on Substrates with Different Hydrophobicity

Abstract

Liquid drop evaporation on surfaces is present in many industrial and medical applications, e.g., printed electronics, spraying of pesticides, DNA mapping, etc. Despite this strong interest, a theoretical description of the dynamic of the evaporation of complex liquid mixtures and nanosuspensions is still lacking. Indeed, one of the aspects that have not been included in the current theoretical descriptions is the competition between the kinetics of evaporation and the adsorption of surfactants and/or particles at the liquid/vapor and liquid/solid interfaces. Materials formed by an electrically isolating solid on which a patterned conducting layer was formed by the deposits left after drop evaporation have been considered as very promising for building electrical circuits on flexible plastic substrates. In this work, we have done an exhaustive study of the evaporation of nanosuspensions of latex and hydrophobized silver nanoparticles on four substrates of different hydrophobicity. The advancing and receding contact angles as well as the time dependence of the volume of the droplets have been measured over a broad range of particle concentrations. Also, mixtures of silver particles and a surfactant, commonly used in industrial printing, have been examined. Furthermore, the adsorption kinetics at both the air/liquid and solid/liquid interfaces have been measured. Whereas the latex particles do not adsorb at the solid/liquid and only slightly reduce the surface tension, the silver particles strongly adsorb at both interfaces. The experimental results of the evaporation process were compared with the predictions of the theory of Semenov et al. (Evaporation of Sessile Water Droplets: Universal Behavior in the Presence of Contact Angle Hysteresis. Colloids Surf. Physicochem. Eng. Asp. 2011, 391 (1-3), 135-144) and showed surprisingly good agreement despite that the theory was developed for pure liquids. The morphology of the deposits left by the droplets after total evaporation was studied by scanning electronic microscopy, and the effects of the substrate, the particle nature, and their concentrations on these patterns are discussed.

Revisiting Wetting, Freezing, and Evaporation Mechanisms of Water on Copper

“…Because of the short time, the evaporation at the beginning (just after the droplet deposition, during its spreading) can be neglected 26 , 27 and this is confirmed by our results (see Figure 7 C). However, it is hardly to find the second stage of evaporation (at constant angle and decreasing contact area), excepting the system Cu0 ( Figures 7 A and 7 C).…”

Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

“…The main details of the theory that describes the first and second evaporation stages of pure fluids-that is also suitable for describing the first evaporation stage of more complex systems, such as surfactant mixtures or nanosuspensions-are summarized in the Appendix [18,19].…”

“…Droplets of the samples (2-4 μL) were manually dispensed using a Hamilton microliter syringe (SN 701, 10 μL). This droplet size is suitable for ensuring that the spherical cap shape is maintained [18] and to avoid any significant buoyancy convection effects [58,59]. The droplets were carefully placed on the surface of the substrate (Silicon wafers, 2.54 cm of diameter, from Siltronix, France) by bringing the droplet formed at the tip of the syringe in direct contact with the substrate surface.…”

“…It should be pointed out that this agreement is universal irrespective of the humidity condition. The theoretical description of the first stage of evaporation, as summarized by Semenov et al [39], has been shown to sufficiently explain the evaporation behaviors of pure liquid [18,39], micro-and nano-suspensions [18,93] and surfactant solutions [19] on solid substrates. The agreement for complex fluids is rather surprising due to the competition between the evaporation kinetics and the adsorption kinetics at the liquid/vapour and the solid/liquid interfaces [96].…”

“…Furthermore, the behavior of such systems depends on the nature of the components, the structures formed in the bulk and their adsorption kinetics at both the liquid/vapor and solid/liquid interfaces [13][14][15][16][17]. It is worth mentioning that the application of theories accounting for the behavior of pure fluids provides a semiquantitative prediction of the first stage of evaporation when nanoemulsions [18] and surfactant solutions [19] are concerned. The removal of the excess solvent from droplets of colloidal suspensions can lead to deposits of solutes onto substrates whose surfaces are usually rough.…”