Evaporation dynamics of completely wetting drops on geometrically textured surfaces

Abstract

-This study deals with the evaporation dynamics of completely wetting and highly volatile drops deposited on geometrically textured but chemically homogeneous surfaces. The texturation consists in a cylindrical pillars array with a square pitch. The triple line dynamics and the drop shape are characterized by an interferometric method. A parametric study is realized by varying the radius and the height of the pillars (at fixed interpillar distance), allowing to distinguish three types of dynamics: i) an evaporation-dominated regime with a receding triple line; ii) a spreading-dominated regime with an initially advancing triple line; iii) a cross-over region with strong pinning effects. The overall picture is in qualitative agreement with a mathematical model showing that the selected regime mostly depends on the value of a dimensionless parameter comparing the time scales for evaporation and spreading into the substrate texture. Introduction. -Wetting and evaporation of liquid drops on solid surfaces are of prime importance for a wide range of applications, from biomedicine and operation of DNA chips to painting and design of self-cleaning and antifouling surfaces. On the other hand, the recent development of small-scale fabrication techniques enables producing surfaces with well-defined chemical and/or geometrical textures, in the micron-range or even at the nanoscale. This offers a large range of new research possibilities, aiming in particular to improve the fundamental knowledge of wetting and evaporation/condensation of liquids on textured surfaces. In turn, a very promising outcome of such improved basic understanding could be the targeted manufacturing of novel hierarchical structures with potential applications in photovoltaics, substrates for engineered cell growth or other smart materials [1].In this work, we focus on surfaces geometrically textured by an array of cylindrical pillars with controlled dimensions (typically tens of microns). Previous studies have shown how such large-scale "roughness" influences the wetting of a drop deposited on the surface [2-4] by enhancing its wettability or non-wettability (i.e., by affecting its apparent contact angle and wetting surface). These works in particular highlighted that, in partial wetting situations, a part of the liquid can invade the surface

Capillary rise and evaporation of a liquid in a corner between a plane and a cylinder: A model of imbibition into a nanofiber mat coating

“…Only in a few works the evaporation during spreading and imbibition has been taken into account in a numerical model. Mekhitarian et al [24] studied experimentally and theoretically imbibition and evaporation of a volatile liquid drop into a textured surface made of cylindrical pillars (of the order of tens of micron), where the radii and heights if the pillars were varied maintaining constant distance between the pillars. The authors have found that for small pillars evaporation-dominated regime prevails, in which imbibition does not take place.…”

Interferometric Imaging of Solvent Vapor of Evaporating Liquid Films

“…Previous work has already been on studying the vapor cloud in the vicinity of a droplet using interferometry, both qualitatively and quantitatively. − Dehaeck et al used a Mach–Zehnder interferometer to investigate pendant drops . Due to the small size of the droplet, the authors were bound to use a highly volatile liquid with a high refractive index of the vapor compared to the refractive index of pure ambient air.…”

Evaporation versus imbibition in a porous medium

“…A particular attention is paid to the identification of the key dimensionless numbers characterizing the system, to the analysis of the limiting cases, and to the characterization of the different possible regimes for the liquid front dynamics. The model enables, inter alia, to analyze the competition between the capillary-driven imbibition and the evaporation on a large range of parameters, which has never been properly tackled so far, whereas it can lead to drastically different liquid front dynamics depending on the dominating mechanisms, as revealed in similar systems [43]. The influence of the liquid and porous medium properties, as well as of the atmospheric conditions, on the liquid front dynamics is also discussed.…”