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
New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University
Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
26.06.2017 | Life Sciences
26.06.2017 | Physics and Astronomy
26.06.2017 | Information Technology