Stick–Slip of Evaporating Droplets: Substrate Hydrophobicity and Nanoparticle Concentration

Abstract

The dynamics of the three-phase contact line for water and ethanol is experimentally investigated using substrates of various hydrophobicities. Different evolutions of the droplet profile (contact line, R, and contact angle, θ) are found to be dependent on the hydrophobicity of the substrate. A simple theoretical approach based on the unbalanced Young force is used to explain the depinning of the contact line on hydrophilic surfaces or the monotonic slip on hydrophobic substrates. The second part of the article involves the addition of different quantities of titanium oxide nanoparticles to water, and a comparison of the evaporative behavior of these novel fluids with the base liquid (water) on substrates varying in hydrophobicity (i.e., silicon, Cytop, and PTFE) is presented. The observed stick-slip behavior is found to be dependent on the nanoparticle concentration. The evaporation rate is closely related to the dynamics of the contact line. These findings may have an important impact when considering the evaporation of droplets on different substrates and/or those containing nanoparticles.

Evaporation of sessile drops: a three-dimensional approach

“…Sefiane & Tadrist (2006), Moffat et al (2009), and Orejon et al (2011). The dynamics of this are dictated by a competition between pinning forces on one hand and depinning forces on the other.…”

“…The dynamics of this are dictated by a competition between pinning forces on one hand and depinning forces on the other. The former are usually due to the contact line being anchored to the substrate because of chemical and surface heterogeneities; the depinning forces are normally the result of the deviation of the droplet profile from equilibrium (Orejon et al 2011). Before these works, Shanahan (1995) had already developed a simple theory to explain the jumps characteristic of the SS mode experienced by the drops in the last stages of the evaporation process.…”

Self-organized Archimedean spiral pattern: Regular bundling of fullerene through solvent evaporation

“…Recently, regular structures that are generated through the deposition of various building blocks, such as colloidal particles [1,2], nanowires [3], nanoparticles [4], quantum dots [5] and macromolecules [6], have been attracting considerable interest as a unique method for surface treatment and the fabrication of micro-devices [7][8][9]. Various methods of surface patterning have been developed for the "bottom-up" fabrication of functional structures [10][11][12][13][14][15][16][17].…”

Tomographic PIV measurement of internal complex flow of an evaporating droplet with non-uniformly receding contact lines

“…(9)(10)(11)(12) This non-uniformly receding contact line pattern is due to various reasons, e.g. heterogeneities of the surface, impurities inside the droplet, and so on.…”

“…heterogeneities of the surface, impurities inside the droplet, and so on. Orejon et al (12) presented that the repetitive pinning and non-pinning motion is dependent on the colloids concentration in the vicinity of the contact line. However, for the stick-and-slip contact line motion of evaporating droplet, the quantitative flow field measurement is still lacking, which we aim to achieve in this work.…”