Remarkable liquid materials called colloids stiffen under impact. Researchers funded by the SNSF have studied the effect of powerful impacts such as those produced by firearms or micrometeorites.
At first glance, colloids resemble homogeneous liquids such as milk or blood plasma. But in fact they consist of particles in suspension. Some colloids have remarkable properties: they may stiffen following an impact and absorb surface shocks. This property is of interest for many applications, from bulletproof vests to protective shields for satellites.
Researchers funded by the Swiss National Science Foundation (SNSF) found that how these colloids work can change dramatically in response to very strong impacts. The scientists have also developed a model that makes these properties easier to understand. The work has been published in the journal PNAS.(*)
SNSF professor Lucio Isa and his team at ETH Zurich create so-called two-dimensional colloidal crystals. The crystals consist of silica beads several thousandths of a millimetre in diameter in a mixture of water and glycerine. In collaboration with Chiara Daraio of Caltech (USA) and Stéphane Job at the Institut supérieur de mécanique de Paris, the researchers studied how this type of material absorbs shocks.
The team observed that when the colloidal particles are micrometre-sized, the force and speed of impact change how the shocks are absorbed. Below a certain threshold, the viscosity of the liquid is the determining factor, and classical models describe the phenomenon very well.
"You have to imagine these tiny glass beads in their liquid," says Isa. "During an impact, the beads move and disperse the fluid around them, more or less rapidly depending on its viscosity. The movement of the fluid is what causes the whole thing to stiffen."
When the shock is particularly intense, the liquid no longer flows between the beads, and they deform. "In this situation, the physical properties of the beads strongly influence shock absorption, and the usual equations no longer apply," says Isa.
Impact of a bullet
For the particles to have an effect, the impact must be extremely intense, such as that caused by a firearm or micrometeorites (objects the size of grains of sand capable of hitting satellites at the speed of ten kilometres per second).
"It was not easy to generate impacts of this intensity in the laboratory," explains Isa. To do so, the researchers covered a small percentage of the silica beads with gold. When exposed to pulsed laser light, the gold evaporated, producing a powerful shock wave in the colloid comparable to that caused, say, by the impact of a micrometeorite.
Ultra-high-speed cameras recorded the action through the lens of a microscope.
"Colloids displaying such properties are really interesting materials to study," says Isa. "For instance, they may even be used for the future development of shields protecting satellites against micrometeorite impacts."
This research was conducted at ETH Zurich, Supméca – Institut supérieur de mécanique de Paris and Caltech. The research was funded by the SNSF and by the Metaudible project under the aegis of the French National Research Agency (ANR) and the Fondation de Recherche pour l'Aéronautique et l'Espace (FRAE).
(*) I. Buttinoni et al.: Direct observation of impact propagation and absorption in dense colloidal monolayers. PNAS (2017) doi: 10.1073/pnas.1712266114
Prof. Lucio Isa
Laboratory for Interfaces, Soft Matter and Assembly
Department of Materials
Phone: +41 44 633 63 76
http://www.snf.ch/en/researchinFocus/newsroom/Pages/news-171108-press-release-li... 'Image available for media use'
http://www.pnas.org/content/early/2017/10/25/1712266114.short?rss=1 'doi: 10.1073/pnas.1712266114'
Media - Abteilung Kommunikation | idw - Informationsdienst Wissenschaft
Watching atoms move in hybrid perovskite crystals reveals clues to improving solar cells
22.11.2017 | University of California - San Diego
Fine felted nanotubes: CAU research team develops new composite material made of carbon nanotubes
22.11.2017 | Christian-Albrechts-Universität zu Kiel
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
22.11.2017 | Business and Finance
22.11.2017 | Physics and Astronomy
22.11.2017 | Physics and Astronomy