Lotus blossoms are beautiful, and always immaculately clean. Water drops bead up and roll off of their water-repellent surface, washing away every speck of dust. This type of self-cleaning surface would be very useful to us as well: no more carwash, no soiled facades on houses—the potential uses are endless. To date, however, technology has not been able to duplicate nature’s success. Researchers led by Kingo Uchida and Shinichiro Nakamura have now synthesized a compound in the diarylethene family whose surface becomes super-water-repellent on command.
The secret behind the lotus effect is the special microstructure, consisting of tiny nubs, on the surface of the lotus plant’s leaves. These micronodules provide no surface on which water drops can collect, so the leaf does not get coated with water. The drops contract into beads and roll off the surface, sweeping away any particles of dirt they encounter on the way. On normal smooth surfaces, water drops coat the surface and assume a hemispherical shape. Instead of rolling, they then glide over the surface, which does not allow them to remove dirt particles.
The Japanese researchers have now synthesized a special substance, a member of the group of compounds known as diarylethenes, and produced a microcrystalline film of this substance on a support. Electron microscopy images show that the surface of this film is initially smooth. When the diarylethene film is irradiated with UV light, the previously colorless surface turns blue—and is no longer smooth. Instead it is covered with a fine down of tiny fibers that have a diameter of about 1 µm. This down has a similar effect to the micronodules on the lotus blossom, resulting in a super-water-repellent surface. If the surface is irradiated again, this time with visible light, the fibers and color vanish, leaving a colorless, smooth, and wettable surface.
This effect originates from changes in the molecular structure. The diarylethene molecule is made of three five-membered rings hooked together. UV light sets off a rearrangement within the molecule (isomerization). This results in a ring closure, which leads to formation of a fourth ring. The isomer with the closed fourth ring crystallizes in the form of needles, which grow out of the crystals of the isomer with the open ring as soon as a certain concentration is reached. Light in the visible range of the spectrum sets off the reverse reaction: the ring re-opens, and the needles disappear.
Author: Kingo Uchida, Ryukoku University, Otsu (Japan), http://www.chem.ryukoku.ac.jp/~uchida/UchidaLab5a.htm
Title: Photoinduced Reversible Formation of Microfibrils on a Photochromic Diarylethene Microcrystalline Surface
Angewandte Chemie International Edition, doi: 10.1002/anie.200602126
| Angewandte Chemie
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Trade Fair News
16.01.2017 | Automotive Engineering
16.01.2017 | Life Sciences