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!
Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH
Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences