Scientists rediscover selfhealing silicone mechanism from the 1950s

first_img New nanotube material stays rubbery over a more than 1,000 degree temperature range The researchers, grad student Peiwen Zheng and Professor Thomas J. McCarthy from the University of Massachusetts, have published a paper on the rediscovery of siloxane equilibration in a recent issue of the Journal of the American Chemical Society.“We have been working on silicone materials from a couple of different perspectives,” Zheng told PhysOrg.com. “When we rediscovered the forgotten unusual properties of silicones and combined them with today’s research interests, we found that the silicone material with the siloxane equilibration was an obvious candidate for a self-healing material.”The researchers performed several experiments to test the theoretical predictions from papers published in the early 1950s, as well as to extend some of the experiments performed at that time. In one experiment, Zheng and McCarthy prepared a siloxane-based mixture containing a cross-linking agent and a catalyst. Then they poured the solution into molds of various shapes, such as cylinders, disks, and dog bones. After heating the molds at 90 °C (194 °F) for four hours, the researchers removed clear, rubbery silicone shapes from the molds. The scientists described these silicone samples as “living polymer networks.” More information: Peiwen Zheng and Thomas J. McCarthy. “A Surprise from 1954: Siloxane Equilibration Is a Simple, Robust, and Obvious Polymer Self-Healing Mechanism.” Journal of the American Chemical Society. DOI: 10.1021/ja2113257 (PhysOrg.com) — Research in self-healing organic polymers has grown recently, but one simple self-healing mechanism from more than 60 years ago has been nearly forgotten until now. Using this mechanism, which is called “siloxane equilibration,” scientists have demonstrated that silicone rubber that has been cut in half with a razor blade can completely repair itself through heat-activated reversible bonding. The self-healing mechanism could have applications in a variety of areas, such as for designing self-healing surfaces of vehicles and countertops. Citation: Scientists rediscover self-healing silicone mechanism from the 1950s (2012, January 30) retrieved 18 August 2019 from https://phys.org/news/2012-01-scientists-rediscover-self-healing-silicone-mechanism.html © 2011 PhysOrg.com (A) A silicone sample started off in the shape of a dog bone. (B) The sample was cut into pieces and rearranged in a dog mold. (C) The sample was remolded into a dog, in which the fracture locations are undetectable. Image credit: Zheng, et al. ©2012 American Chemical Society “The silicone network is at a chemically anionic equilibrium,” Zheng explained of the term, “where the reactive center will cleave and reform a covalent siloxane bond.” These bonds are reversible, which enables the two sides of a crack to reconnect under the right conditions.To demonstrate the self-healing ability, the researchers cut a 1-cm-long cylindrical sample in half using a razor blade. Then they rejoined the two pieces by wrapping them together with Teflon plumbing tape and heating them in an oven at 90 °C (194 °F) for 24 hours. When the researchers retrieved the sample and removed the tape, they found that the silicone cylinder had completely healed. Then they bent the cylinder by hand until it broke again – significantly, it broke in a different location than where it had been cut. The scientists repeated this experiment on different shaped objects with the same results. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Journal information: Journal of the American Chemical Society In another experiment, the researchers molded a silicone dog bone, which they cut into multiple pieces. Then they rearranged the pieces to fit into a mold of a dog. Heating the sample resulted in a silicone dog with no visible fractures or weak spots where the pieces had been fitted together.The researchers also quantified the strength of the healed samples in comparison with the original samples using fracture toughness measurements. The data for the two types of samples was indistinguishable, indicating exceptional self-healing.The researchers explained that, in principle, any cross-linked dimethylsilicone elastomer (only one type was used here) can be converted into a living elastomer by the addition of basic catalysts. This possibility opens up many different routes for synthesizing a variety of self-healing silicione-based materials. While the samples used here required applied heating to self-heal, the researchers predict that samples in a sealed, high-temperature environment would self-heal “autonomically,” or automatically. Zheng explained that self-healing materials, with some improvements, could lead to a variety of applications.“It can be developed into self-healing coatings on auto vehicles or countertops,” she said. “It is also a ‘plastic’ elastomer which can be used in molding to form desired shapes and patterns. The concept of a self-healing silicone can be used to guide the preparation of elastomers with gradient modulus, Janus elastomers, reversible surface patterns when filled with magnetic particles, and super tough materials which can chemically relax stress.” Explore further (A) A silicone sample in the shape of a cylinder. (B) The sample was cut in half with a razor blade. (C) The sample completely self-healed after 24 hours at high temperatures. (D) When the healed sample was bent by hand, it broke in a different location than where it had been cut. Image credit: Zheng, et al. ©2012 American Chemical Societylast_img read more

We love the way you look in Cardinals red but the

first_imgWe love the way you look in Cardinals red, but the @ProFootballHOF gold jacket suits you well, @Kurt13Warner!Congrats!(🎥 @nflnetwork) pic.twitter.com/EaRtZwhtsc— Arizona Cardinals (@AZCardinals) August 5, 2017Former Arizona Cardinals quarterback and Ring of Honor member Kurt Warner received his gold jacket Friday before his Pro Football Hall of Fame induction Saturday.Warner made his entrance at the Gold Jacket Ceremony greeting several current Hall of Famers and joking with them along the way. Derrick Hall satisfied with D-backs’ buying and selling .@Kurt13Warner makes his entrance at the @ProFootballHOF Gold Jacket Ceremony!Coverage on @NFLNetwork pic.twitter.com/Es10ZRPrHj— Arizona Cardinals (@AZCardinals) August 5, 2017One of those was former Cardinal Aeneas Williams. So excited for my teammate & brother Kurt W. congrats bro! Gold Jacket is Next! pic.twitter.com/DvDhcZ1G5C— Aeneas Williams (@aeneas35) August 5, 2017The lead-up to Warner receiving the jacket included a video package on his career. Grace expects Greinke trade to have emotional impact Top Stories center_img You made it to Canton!Congrats to our @kurt13warner! 👏👏👏#PFHOF17 pic.twitter.com/k388xI9uB9— NFL Network (@nflnetwork) August 5, 2017Warner was emotional afterward, struggling to process the moment.“I’m still trying to figure it all out,” Warner said of receiving the jacket. “When you watch these guys lined up, guys who I watched play, guys who I tried to emulate, guys that I played with and understand their greatness, I’m not sure how I fit into that mix yet.”Warner said he isn’t sure if he will wear the jacket much, but like his Super Bowl ring that he also doesn’t wear much, he will admire it and reflect on the journey he had with his teammates. 2 Comments   Share   The 5: Takeaways from the Coyotes’ introduction of Alex Meruelo Former Cardinals kicker Phil Dawson retireslast_img read more