Water repellent properties, Biomimicry, Self assembling molecules, Network of micro- and nanowires-Link to Resources, excellent imagery, it’s all in this short news article from Nature Asia-Pacific (NPG Asia Mater)
Chinese scientists have created an artificial water strider to show off the remarkable water-repelling properties of a new material.
We learn of Water Striders, insects that can float on the surface of a pond due to the microscopic hairs that coat their legs. These hairs trap tiny bubbles of air, giving them enough buoyancy to skim over water.
Self assembling molecules form a network of micro- and nanowires, a simple process!
Wenping Hu, Lei Jiang and colleagues at the Beijing National Laboratory for Molecular Sciences, part of the Chinese Academy of Sciences1, have now mimicked the insect with the help of an anthracene-based molecule. The scientists made their water-repelling films by simply dropping a solution of the molecule onto a glass plate. As the solvent evaporated, the molecules self-assembled into a network of micro- and nanowires.
Scientific principles made simple
The molecule itself is not particularly water-repellent, since it contains two cyano (CN) groups that can form weak bonds with water. [lower the surface tension of water] But when the molecules are stacked into a wire, these cyano groups are turned inwards, leaving the water-repelling parts of the molecule facing outwards. The team found that water beaded into near-spherical droplets on top of the film (Fig.1 images), and that the wires had a rough surface that was ideal for trapping air bubbles.
These two properties allowed the team to create an artificial Water Strider using copper foil and wires for its body and legs. Although it was roughly the same size as a real water strider, at 260 milligrams it weighed at least 26 times as much.
When the anthracene derivative was coated onto the legs, the strider could stand on water without sinking (Fig. 1-images). By loading the strider with more copper foil, the scientists showed that just a milligram of the anthracene molecule was enough to support more than 300 times as much copper. Further experiments showed that the coating increased the supporting force of the leg by at least 2.4 times.
The scientists hope that their inexpensive and simple technique for making water-repelling films could be applied in a variety of ways, including helping to create water-walking robots.
Post Scriptum-comment and further references
1. Environmental pollution can modify the surface tension of water Woodrow Wilson Foundation Leadership Programme for Teachers Princeton Faculty
2. Surface Tension on Hyperphysics' Site
3. Nano Networks more…
4. Images more science and engineering