Impalement of fakir drops

Abstract

Water drops deposited on hydrophobic materials decorated with dilute micro-posts generally form pearls. Owing to the hydrophobicity of the material, the drop sits on the top of the posts. However, this "fakir state" is often metastable: if the drop impales inside the texture, its surface energy is lowered. Here we discuss the transition between these two states, considering the drop size as a parameter for inducing this transition: remarkably, it is found that a drop impales when it becomes small, which is interpreted by considering its curvature. This interpretation allows us to propose different recipes for avoiding this detrimental effect.

Direct Observation of the Wetting Mode Transition during Evaporation of Water Droplets on Superhydrophobic Surfaces with Random Roughness Structure

“…Few investigations have examined this phenomenon using a surface with random roughness because of the difficulties in (1) Very recently, we successfully detected the wetting mode transition of water during evaporation on two superhydrophobic surfaces with different random roughness sizes using nanoliterscale droplets 27) . Moreover, in that study, we demonstrated that the wetting mode transition radii of a water droplet calculated from the model of Reyssat et al 25) using the relation between the average roughness distance (Rsm) and the average roughness height (Rc) of the random structure on each surface were close to the experimental values. In this study, we used top and side views to observe evaporation or penetration behavior of ultrasmall water droplets (80 -100 nL) on superhydrophobic surfaces with fine random roughness during evaporation.…”

“…This transition commonly accompanies an increase of contact angle hysteresis 8,11) . The stability on each wetting mode has been evaluated from the perspective of surface structure and energy balance [14][15][16][17][18][19][20][21][22][23][24][25][26] .…”

Regimes of wetting transitions on superhydrophobic textures conditioned by energy of receding contact lines

“…This behavior results from an impalement of the drop in the texture. 7 Note that the impalement time is well below 40 ms. We remark that these observations are qualitatively similar to made before for dilute pillars. 12,33 For dense patterns the evaporation occurs in two stages (see Fig.…”

“…[24][25][26] We study a wetting transition by monitoring the evaporation of a drop. An evaporating drop is known to produce various intriguing phenomena, such as coffee stains 27 or wine tears, 28 and has been already studied with isotropic SH surfaces, 7,29,30 although the quantitative understanding is still at its infancy. During the evaporation the drop becomes smaller and the contact angle retracts.…”

Wetting state on hydrophilic and hydrophobic micro-textured surfaces: Thermodynamic analysis and X-ray visualization

“…Although wetting state has been extensively explored in previous reports, 13,14,16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] the majority of these previous reports have focused on hydrophobic textured surfaces. Besides the wetting state was inferred from visible-wavelength images, making it difficult to identify the physical behavior at the vicinity of the micro-pillars on the test surfaces.…”