Testing surface adhesion

With a nod to one of nature’s best surface chemists - an obscure desert beetle - polymer scientists at the National Institute of Standards and Technology (NIST) have devised a convenient way to construct test surfaces with a variable affinity for water, so that the same surface can range from superhydrophilic to superhydrophobic, and everything in between.

Their technique, reported in a recent issue of the journal Langmuir, may be used for rapid evaluation of paints and other materials that need to stick to surfaces.

The NIST team developed a flexible technique, based on ultraviolet light and photosensitive materials, to mimic one of nature’s cleverest feats of surface chemistry.

The Stenocara beetle of Africa’s Namib Desert is able to thrive in a habitat so parched that not even the morning fog will condense. All the beetle has to do is raise its warty-looking wing covers into the breeze. Because the bumps are hydrophilic, or water-attracting, while the rest of the surface is hydrophobic, or water-repelling, the few water molecules that do strike the wing covers tend to get pushed uphill and collect on the bumps - where they eventually condense into artificial dewdrops that roll into the insect’s mouth. The insect’s trick is to use both surface structure and chemistry to create a surface that shifts rapidly from hydrophobic to hydrophilic.