Now a Duke and Stanford chemistry team has found a polymer molecule that's so springy it snaps back from stretching much smaller than it was before.
Duke graduate student Jeremy Lenhardt and associate professor Stephen Craig have been systematically hunting through a library of polymers in search of a molecule that might be useful for "self-healing" materials. They hope to find a polymer that can trigger a chemical reaction when it is stretched and enable a material to build its own repairs.
Imagine a sheet of Saran Wrap that could fix a microscopic puncture before the hole ever got big enough to see. This would require that the polymer molecules immediately around the tear could somehow jump into action and perform new chemistry to build bridges across the hole.
To stretch polymers and see what happens to them, Lenhardt uses an apparatus that pumps up and down on a solution filled with polymers, pressurizing it and depressurizing it 20,000 times a second which causes tiny bubbles to form fleetingly. The void created by the bubbles exerts a tug on the ends of some of the polymers in the solution and stretches them, if only for a billionth of a second.
"Think of two rafts going down a river with a rope between them," Craig explained. "As the first raft enters a rapids and accelerates forward, that rope – the polymer – gets pulled taught and stretches."
Over and over Lenhardt ran the experiment, characterizing different polymer species that became more reactive when stretched, potentially able to do "stress-induced chemistry."
Then, while looking at polymers that contained tiny ring-shaped molecules called gem-difluorocyclopropanes (gDFC), he was surprised to find that some of these molecules emerged from the stretching noticeably shorter than when they went in.
"I ran up to his office," Lenhardt said. " 'Steve, something funny is going on here. Look at this!' " A technique called nuclear magnetic resonance had revealed the shapes of the rings after pulling and shown that they were, in fact, shorter.
But not only were the gDFCs snapping back smaller than they started, it also appeared that before snapping back they were actually trapped in an unusual stretched state far longer than normal, a reactive state called a 1,3-diradical.
Normally, as a molecule goes through a reaction, it passes through a special point known as a transition state, and stays there for only ten to a hundred femtoseconds, "a tenth of a millionth of a millionth of a second," Craig said. This makes it extraordinary hard to actually watch chemistry happen, so chemists usually can only infer what happens at the transition state by what they've seen before and after.
Work by their Stanford collaborators showed that the trapped 1,3-diradicals are in fact one type of these usually fast-moving transition states, but in Lenhardt's experiments they were essentially stopped in their tracks and trapped for nanoseconds, tens of thousands of times longer than usual.
This might be a window for watching transition states in action, Craig said. "We can trap these things long enough to probe new facets of their reactivity."
Lenhardt has begun doing just that, stretching the polymers to learn more about these transition states and seeing if he can watch other molecules by using this technique as a sort of stop-action camera.
"Every chemical reaction has a high energy state that you have to guess at," Lenhardt said. "But maybe, in some cases, you don't have to guess anymore."
The team's findings appear Aug. 27 in Science.
Other team members include Duke undergraduate Robert Choe and at Stanford, graduate student Mitchell Ong, postdoc Christian Evenhuis and professor Todd Martinez.
The research was funded by the U.S. Army Research Laboratory and the Army Research Office.
Karl Leif Bates | EurekAlert!
Symbiotic bacteria: from hitchhiker to beetle bodyguard
28.04.2017 | Johannes Gutenberg-Universität Mainz
Nose2Brain – Better Therapy for Multiple Sclerosis
28.04.2017 | Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences