Drop mobility on superhydrophobic microstructured surfaces with wettability contrasts

Abstract

Influence of wettability contrasts and contact angle hysteresis on drop velocity and surface energy analysis describing the drop motion.

Condensation on Surfaces With Biphilic Topography: Experiment and Modeling

“…Results showed a great potential of using such surfaces with heat transfer performance bounded by the two extreme cases, i.e., film and drop wise condensation. After this work, several researchers studied different configurations, such as biphilic strips (Drelich et al, 1996;Morita et al, 2005;Megaridis et al, 2016;Zou et al, 2018), biphilic dotted surfaces (Raj et al, 2012) and biphilic pillars (Kita et al, 2018).…”

Droplet motion on contrasting striated surfaces

“…Previous work has demonstrated that surface structure and, more specifically, surface microstructure can also be exploited to finely tune the surface wettability, thus creating an alternative method to activate droplet motion. [20][21][22][23][24][25][26] Compared to the methods above, making use solely of surface structure with a uniform chemical coating or structuring an intrinsically hydrophobic material provide advantages such as chemical stability, robustness and precise wettability adjustment without the need for external disturbances, making it an ideal choice as microfluidic systems.…”

“…The motion of a liquid droplet sitting in the Cassie-Baxter (CB) state 27 on intrinsically hydrophobic microstructures with small hysteresis can be induced by a roughness gradient towards the region where its (effective) free surface energy is lower, once it has overcome hysteresis. [21][22][23]26 Additionally, external forces such as vibrations and coalescence have been exploited to overcome droplet adhesion and/or hysteresis in the presence of micropillars, 23,24 since otherwise the motion is limited. 22 However, spontaneous movement can be achieved on micro-striations with high length to width aspect ratio, for a much longer distance with only the help of the initial deposition energy and roughness gradient.…”

“…[21][22][23]26 Additionally, external forces such as vibrations and coalescence have been exploited to overcome droplet adhesion and/or hysteresis in the presence of micropillars, 23,24 since otherwise the motion is limited. 22 However, spontaneous movement can be achieved on micro-striations with high length to width aspect ratio, for a much longer distance with only the help of the initial deposition energy and roughness gradient. 21 Further, micro-striated surfaces are expected to provide higher mobility and greater displacements along the striation direction 28,29 when compared to micropillared ones where the ratio of discontinuous segments of contact line length to surface area is greater.…”

“…In the past, droplet motion on asymmetrical microstructures has been predicted by making use of simulations, 33,34 while other works have addressed a limited number of structural and wetting contrasts experimentally. 22,23,26 However, systematic experimental work exploring a wider range of wetting contrasts, i.e., both average solid fraction and contrasting fraction, is necessary to develop a unified understanding of how motion of droplets can be controlled by surface structure. This is of paramount importance for the formulation of the design guidelines for microfluidic devices and applications that need fine droplet control.…”