A liquid that changes its color “on demand” and can take on any color of the rainbow one desires? A research team headed by Yadong Yin at the University of California, Riverside (USA) has now shared the secret of their wonderful liquid with the journal Angewandte Chemie: Nanoscopic particles made of tiny magnetic crystals coated with a plastic shell self-assemble in solution to form photonic crystals—semiconductors for light. When a magnetic field is applied, the optical properties of the crystals change, allowing their color to be very precisely adjusted through variation of the strength of the field.
The crystals involved here are no “conventional” lattices of ions or molecules like the one we are familiar with for salt; instead they are colloidal crystals, periodic structures that form from uniform solid particles that are finely dispersed in a liquid. Colloidal crystals can be produced at little cost and on a large scale—and can be used as photonic crystals. Photonic crystals are the optical analogue of electronic semiconductor materials. Like their electronic counterparts, they have photonic band gaps, forbidden energy levels, or wavelengths, at which the photonic crystal does not transmit light. These optical properties depend on the spatial relationships within the crystal.
Current research is concerned with photonic crystals whose forbidden bands are variable and can be adjusted quickly and precisely in response to an external stimulus. These requirements have been impossible to meet until now.
One stimulus that could be used is a magnetic field, if the crystals are made of magnetic materials, such as iron oxide. The problem with this is that the magnetization is maintained when the particles grow into larger domains (ferromagnetism). Yin and his team have found a solution: They coated nanoscopic iron oxide particles with a plastic called polyacrylate. This results in separate clusters of nanocrystals, which self-assemble in solution to form colloidal photonic crystals. The forces of the magnetic field affect every individual cluster, changing the cluster-to-cluster distances within the crystal lattice. Depending on the distance from the magnet and thus the field strength, the color of the colloidal crystal changes right across the whole visible spectrum. This response is rapid and fully reversible because the nanocrystals in clusters are so small that they lose their magnetism when the magnetic field is shut off (superparamagnetism). Potential applications for these switchable “optical semiconductors” include novel optoelectronic components for telecommunications, displays, and sensors.
Author: Yadong Yin, University of California, Riverside (USA), http://www.chem.ucr.edu/index.html?main=faculty&facsort=profile&faculty=yin
Title: Highly Tunable Superparamagnetic Colloidal Photonic Crystals
Angewandte Chemie International Edition, doi: 10.1002/anie.200701992
Yadong Yin | Angewandte Chemie
Good preparation is half the digestion
15.11.2018 | Max-Planck-Institut für Stoffwechselforschung
How the gut ‘talks’ to brown fat
16.11.2018 | Technische Universität München
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly
The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
15.11.2018 | Earth Sciences
15.11.2018 | Physics and Astronomy
15.11.2018 | Physics and Astronomy