When a water drop bounces back from a hydrophobic surface, its initial, spherical shape is usually restored. Now, experiments with a specially engineered superhydrophobic surface made from micrometre-sized tapered pillars covered with copper oxide ‘nanoflowers’ show that droplets can bounce back with a flat, pancake-like shape. Engineering surfaces that promote rapid drop detachment1,2 is of importance to a wide range of applications including anti-icing3,4,5, dropwise condensation6 and self-cleaning7,8,9. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nanotextures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows a fourfold reduction in contact time compared with conventional complete rebound 1,10,11,12,13. We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures that behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bouncing and rapid drop detachment over a wide range of impact velocities.

Pancake bouncing on superhydrophobic surfaces.

https://pureadmin.qub.ac.uk/ws/files/126683921/Edited_sudagar_R1.pdf

Electroless nickel, alloy, composite and nano coatings – A critical review

Tribology of electroless nickel coatings – A review

Droplet departure frequency is investigated using environmental scanning electron microscopy with implications to enhancing the rate of dropwise condensation on superhydrophobic surfaces. Superhydrophobic surfaces, formed by cupric hydroxide nanostructures, allow the condensate to depart from a surface with a tilt angle of 30° from the horizontal. The resulting decrease in drop departure size shifts the drop size distribution to smaller radii, which may enhance the heat transfer rate during dropwise condensation. The heat transfer enhancement is estimated by modifying the Rose and Le Fevre drop distribution function to account for a smaller maximum droplet size on a superhydrophobic surface.

Visualization of droplet departure on a superhydrophobic surface and implications to heat transfer enhancement during dropwise condensation

Electrochemical reduction of CO2 using renewable energy is a promising strategy to mitigate the CO2 emissions and to produce valuable chemicals. However, the lack of highly selective, highly durable, and nonprecious-metal catalysts impedes the applications of this reaction. In this work, copper-nanowire-supported indium catalysts are proposed as advanced electrocatalysts for the aqueous electroreduction of CO2. The catalysts are synthesized by a facile method, which combines In3+ deposition on Cu(OH)2 nanowires, mild oxidation, and in situ electroreduction procedures. With a thin layer of metallic In deposited on the surface of the Cu nanowires, the catalyst exhibits a CO Faradaic efficiency of ∼93% at −0.6 to −0.8 V vs RHE; additionally, an unprecedented stability of 60 h is achieved. The characterization results combined with density functional theory (DFT) calculations reveal that the interface of Cu and In plays an essential role in determining the reaction pathway. The calculation results suggest tha...

/pdf/selective-and-stable-electroreduction-of-co2-to-co-at-the-4tt8whlebd.pdf

Dong Dong

Papers

Preparation and properties of electroless Ni–P–SiO2 composite coatings

Synthesis and characterization of superhydrophobic functionalized Cu(OH)2 nanotube arrays on copper foil

Different wetting behavior of alkyl- and fluorocarbon-terminated films based on cupric hydroxide nanorod quasi-arrays