Condensation on slippery asymmetric bumps

Abstract

Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena such as anti-reflective structures and contact time of impacting droplets, the effect of the detailed convex topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared to superhydrophobic surfaces. We envision that our fundamental understanding and innovative design of bumps can be applied to lead enhanced performance in various phase change applications including water harvesting.

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…Inspired by nature, [1][2][3][4][5][6][7][8][9][10][11][12][13][14] the special wettability of material surfaces, which is engineered via synergistic utilization of microscale surface structures and surface chemistry has been one of the most active research fields, and it can play a key role in addressing problems related to energy, environment, resources, and health. Efforts in the past decades have explored controllable fabrication, functionality, and performance optimization of bionic superhydrophobic surfaces with a contact angle above 150°, and they have resulted in technological innovations such as self-cleaning, drag-reduction, anticorrosion, antifogging, antifreezing and oil-water separation.…”

Surfaces Inspired by the Nepenthes Peristome for Unidirectional Liquid Transport

“…[6] Without energy input, these biological surfaces can harness the movement of water through their unique structural features and chemical composition, [11][12][13] which gives inspiration for designing and fabricating functional surfaces and materials with wide applications in fields including antifogging and fog-collection, [14][15][16] microfluidic devices, [17][18][19][20][21] lubrication, [22,23] and liquid transport. [24][25][26][27] One-dimensional materials for unidirectional liquid transport, inspired by spider silk and cactus spines, have attracted major research interest in the last few years.…”

Drop mobility on chemically heterogeneous and lubricant-impregnated surfaces

“…Yet, we hope to have given at least the flavour of some new and interesting strategies to passively control the direction of sessile drops by exploiting the pinning barriers exerted by suitable lyophilic/lyophobic patterns printed on a surface and to obtain strong omniphobicity because of the weak pinning arising from the presence of a liquid substrate. These aspects can be synergistically combined to produce new functional surfaces which provide unprecedented droplet growth and transport by mimicking specific mechanisms of different living systems [4].…”

“…Controlling and predicting the mobility of drops in contact with a solid surface is a major scientific challenge, relevant for fundamental research [1] and crucial for an ample variety of applications including self-cleaning coatings [2], microfluidics [3], dropwise condensation [4] and fog collection [5]. The mobility of drops is deeply affected by substrate heterogeneities [6].…”