Control of evaporation by geometry in capillary structures. From confined pillar arrays in a gap radial gradient to phyllotaxy-inspired geometry

Abstract

Evaporation is a key phenomenon in the natural environment and in many technological systems involving capillary structures. Understanding the evaporation front dynamics enables the evaporation rate from microfluidic devices and porous media to be finely controlled. Of particular interest is the ability to control the position of the front through suitable design of the capillary structure. Here, we show how to design model capillary structures in microfluidic devices so as to control the drying kinetics. This is achieved by acting on the spatial organization of the constrictions that influence the invasion of the structure by the gas phase. Two types of control are demonstrated. The first is intended to control the sequence of primary invasions through the pore space, while the second aims to control the secondary liquid structures: films, bridges, etc., that can form in the region of pore space invaded by the gas phase. It is shown how the latter can be obtained from phyllotaxy-inspired geometry. Our study thus opens up a route toward the control of the evaporation kinetics by means of tailored capillary structures.

Evaporation with the formation of chains of liquid bridges

“…Clément & Leng 2004). The present study shows that such a control may be achieved by finely tuning the microsystem design in order to favour, or not, the transport of a liquid by films (see Chen et al 2017).…”

“…Concomitantly with the gas-phase ingress, some elongated liquid films remain trapped along each spiral. In fact, the distances w // between two cylinders along a spiral are typically small enough to allow for coalescence between the liquid clusters left around each cylinder following air invasion, liquid clusters that would otherwise remain isolated (Chen et al 2017). A liquid film can be described as a chain of liquid bridges between…”

“…To that end, we study the drying of a micromodel consisting of cylindrical pillars arranged in a phyllotaxy-inspired spiral pattern (Douady & Couder 1992), and sandwiched between two horizontal flat plates. As discussed in Chen et al (2017), such a design enables the formation of elongated liquid films consisting of 'chains' of liquid bridges between cylinders, as the drying of the initially saturating liquid occurs, which provide long-range connectivity within this model porous medium. Thus, the liquid bridges between two constitutive particles of the solid matrix (i.e.…”

Isolating phyllotactic patterns embedded in the secondary growth of sweet cherry (Prunus avium L.) using magnetic resonance imaging

“…Besides their ubiquity in developing plant structures, phyllotactic features appear in other natural phenomena such as capillary structures during evaporation [25] and the cylindrical phyllotaxy of carbon nanontubes [26]. For a discussion of the universality of Fibonacci patterns in nature, see [27].…”

Effect of Weaving Structures on the Water Wicking–Evaporating Behavior of Woven Fabrics

“…Water transfer begins spontaneously, driven by capillary force, and evaporation takes place at the same time when the fabric is in contact with water [20]. Previous studies concerned with wicking-evaporating have been carried out on nontextile materials [19][20][21][22]. A twill metallic weave was studied and an evaporation rate model for predicting wicking height was proposed by Fries using Lucas and Washburn equations, indicating evaporation rate model for predicting wicking height was proposed by Fries using Lucas and Washburn equations, indicating that the effect of evaporation in the wicking process is evident [21].…”