In many cases, they are nature's ingenious way of packing more surface area into a limited space. Scientists, mimicking nature, have long sought to manipulate surfaces to create wrinkles and folds to make smaller, more flexible electronic devices, fluid-carrying nanochannels or even printable cell phones and computers.
But to attain those technology-bending feats, scientists must fully understand the profile and performance of wrinkles and folds at the nanoscale, dimensions 1/50,000th the thickness of a human hair. In a series of observations and experiments, engineers at Brown University and in Korea have discovered unusual properties in wrinkles and folds at the nanoscale. The researchers report that wrinkles created on super-thin films have hidden long waves that lengthen even when the film is compressed. The team also discovered that when folds are formed in such films, closed nanochannels appear below the surface, like thousands of super-tiny pipes.
"Wrinkles are everywhere in science," said Kyung-Suk Kim, professor of engineering at Brown and corresponding author of the paper published in the journal Proceedings of the Royal Society A. "But they hold certain secrets. With this study, we have found mathematically how the wrinkle spacings of a thin sheet are determined on a largely deformed soft substrate and how the wrinkles evolve into regular folds."
Wrinkles are made when a thin stiff sheet is buckled on a soft foundation or in a soft surrounding. They are precursors of regular folds: When the sheet is compressed enough, the wrinkles are so closely spaced that they form folds. The folds are interesting to manufacturers, because they can fit a large surface area of a sheet in a finite space.
Kim and his team laid gold nanogranular film sheets ranging from 20 to 80 nanometers thick on a rubbery substrate commonly used in the microelectronics industry. The researchers compressed the film, creating wrinkles and examined their properties. As in previous studies, they saw primary wrinkles with short periodicities, the distance between individual wrinkles' peaks or valleys. But Kim and his colleagues discovered a second type of wrinkle, with a much longer periodicity than the primary wrinkles — like a hidden long wave. As the researchers compressed the gold nanogranular film, the primary wrinkles' periodicity decreased, as expected. But the periodicity between the hidden long waves, which the group labeled secondary wrinkles, lengthened.
"We thought that was strange," Kim said.
It got even stranger when the group formed folds in the gold nanogranular sheets. On the surface, everything appeared normal. The folds were created as the peaks of neighboring wrinkles got so close that they touched. But the research team calculated that those folds, if elongated, did not match the length of the film before it had been compressed. A piece of the original film surface was not accounted for, "as if it had been buried," Kim said.
Indeed, it had been, as nano-size closed channels. Previous researchers, using atomic force microscopy that scans the film's surface, had been unable to see the buried channels. Kim's group turned to focused ion beams to extract a cross-section of the film. There, below the surface, were rows of closed channels, about 50 to a few 100 nanometers in diameter. "They were hidden," Kim said. "We were the first ones to cut (the film) and see that there are channels underneath."
The enclosed nano channels are important because they could be used to funnel liquids, from drugs on patches to treat diseases or infections, to clean water and energy harvesting, like a microscopic hydraulic pump.
Contributing authors include Jeong-Yun Sun and Kyu Hwan Oh from Seoul National University; Myoung-Woon Moon from the Korea Institute of Science and Technology; and Shuman Xia, a researcher at Brown and now at the Georgia Institute of Technology. The National Science Foundation, the Korea Institute of Science and Technology, the Ministry of Knowledge Economy of Korea, and the Ministry of Education, Science, and Technology of Korea supported the research.
Richard Lewis | EurekAlert!
Fighting myocardial infarction with nanoparticle tandems
04.12.2017 | Rheinische Friedrich-Wilhelms-Universität Bonn
Virtual Reality for Bacteria
01.12.2017 | Institute of Science and Technology Austria
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy