Three-dimensional capillary ratchet-induced liquid directional steering

Abstract

Surfaces directing fluid flows Although surfaces can be made to attract or repel liquids using coatings, surface textures with specific curvature can also be used to achieve the same effect. However, fluid transport is usually limited by the specific pattern that only drives flow at the surface itself. Feng et al . created a dual-reentrant surface that has an asymmetric profile so that fluids spread out at the surface and subsurface layers. Furthermore, these surfaces can be designed so that different liquids will naturally steer in opposing directions simply because of their specific interactions with the surface. —MSL

Droplet Bouncing: Fundamentals, Regulations, and Applications

“…The droplet bouncing on nonwetting solid surfaces is ubiquitous in nature [16,17] and is important in many industrial processes like spraying, [18] anti-icing, [19][20][21] or self-cleaning. [22] There are three elementary parameters to characterize wetting properties of the solid surface (Figure 2): i) the contact angle θ of the droplet on the solid surface, [23][24][25][26] showing the static wetting property; ii) the contact angle hysteresis CAH = θ advancing -θ receding when droplet moves on the solid surface, [27][28][29][30] being the difference between the advancing angle θ advancing and receding angle θ receding and reflecting the mobility of the droplet on the solid surface; and iii) the sliding angle θ sliding , being the inclined angle of the solid surface when the droplet starts sliding. For droplet bouncing, the nonwetting solid surface typically should possess a high contact angle, a low contact angle hysteresis and a low sliding angle.…”

Controllable Directional Liquid Transport in Open Channel

“…[24][25][26] Various micro-nano structural surfaces with superior liquid transport function, inspired by cactus spine, Araucaria leaf and peristome of Nepenthes alata, etc., have been explored extensively and implemented for fog-collection, lubrication, and pumpless microfluidic devices. [27][28][29] Among those strategies, the Laplace pressure derived from the geometry curvature gradient might be the most feasible one. [30][31][32] However, the regulation of liquid transport direction is difficult to be realized by elaborate design of asymmetric structures.…”

Steerable drops on heated concentric microgroove arrays

“…The ability to deposit drops to obtain desired transport directions in a highly repeatable manner is desired for thermal dissipation with high efficiency, and can also be utilized to perform practical tasks such as drop sieving for fluidic-based applications 29 , 30 . The advantages of our work will largely benefit these concepts, which will be illustrated as follows.…”