Julie Kalista
Online Editor

The same surface ranges from superhydrophilic to superhdryophobic and everything in between.

The flexible technique mimics one of nature's feats of surface chemistry used by the Stenocara beetle of Africa's Namib Desert. The insect's wings have bumps on them that are hydropholic or water-attracting. The rest of the wing's surface is hydrophobic, or water-repelling. Using both surface structure and chemistry, the insect creates a surface that rapidly shifts from hydrophobic to hydrophilic.

With the beetle's technique in mind, NIST researchers created a single surface that tests the entire range of wettability. Their technique is based on ultraviolet light and photosensitive materials, using an optical method that's easier to modulate and can be carried out in the air. Granules on the surface are coated with a photosensitive material and exposed to ultraviolet light. The longer and more intense the exposure in a given area, the more hydrophilic it becomes.

The primary application is for testing paints, adhesives, and other coatings. Instead of spreading compounds on several surfaces one at a time, researchers can now coat a single surface that tests the entire range of wettability. The team is considering using the technique for water collection in dry regions and open-air microchannel devices.

More Information:
NIST

Wetability gradient: Water sprayed on a glass slide coated with a nanostructured gradient wettability film using the NIST technique illustrates the transition from (A) superhydrophobicity to (C) superhydrophilicity. The lower image shows the magnified image of the (A) hydrophobic to (B) transition wetting region. The pink dotted line indicates the border of the superhydrophobic region and the yellow dotted region shows a hydrophobic 'sticky' region.