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Shape and Size Matter – for Designing Water-Repellent Surfaces

Antonio Checco

Brookhaven Lab physicist Antonio Checco

When it comes to designing extremely water-repellent surfaces, shape and size matter. That's the finding of a group of scientists at Brookhaven, who investigated the effects of differently shaped, nanoscale textures on a material's ability to force water droplets to roll off without wetting its surface. These findings and the methods used to fabricate such materials are highly suitable for a broad range of applications where water-resistance is important, including power generation, transportation, and diagnostics.

"The idea that microscopic textures can impart a material with water-repellent properties has its origins in nature," explained Brookhaven physicist and lead author Antonio Checco. "For example, the leaves of lotus plants and some insects' exoskeletons have tiny-scale texturing designed to repel water by trapping air. This property, called 'superhydrophobicity' (or super-water-hating), enables water droplets to easily roll off, carrying dirt particles along with them."

Mimicking this self-cleaning mechanism of nature is relevant for applications, such as non-fouling, anti-icing, and antibacterial coatings. However, engineered superhydrophobic surfaces often fail under conditions involving high temperature, pressure, and humidity. So scientists have been looking for schemes to improve the performance of these surfaces. 

The Brookhaven team created and tested new materials with different nanoscale textures—some decorated with tiny straight-sided cylindrical pillars and some with angle-sided cones. They were also able to control the spacing between these nanoscale features to achieve robust water repellency. While several different nanotextures significantly increased the water repellency, scientists found the cone-shaped nanostructures were significantly better at forcing water droplets to roll off the surface, thus keeping surfaces dry.

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