Polymer science has made attainable rubber tires, Teflon and Kevlar, plastic water bottles, nylon jackets amongst many different ubiquitous options of each day life. Elastic polymers, often known as elastomers, will be stretched and launched repeatedly and are utilized in functions reminiscent of gloves and coronary heart valves, the place they should final a very long time with out tearing. But a conundrum has lengthy stumped polymer scientists: Elastic polymers will be stiff, or they are often powerful, however they can not be each.
This stiffness-toughness battle is a problem for scientists growing polymers that might be utilized in functions together with tissue regeneration, bioadhesives, bioprinting, wearable electronics, and smooth robots.
In a paper revealed in the present day in Science, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have resolved that long-standing battle and developed an elastomer that’s each stiff and difficult.
“In addition to developing polymers for emerging applications, scientists are facing an urgent challenge: Plastic pollution,” mentioned Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials, the senior creator of the research. “The development of biodegradable polymers has once again brought us back to fundamental questions—why are some polymers tough, but others brittle? How do we make polymers resist tearing under repeated stretching?”
Polymer chains are made by linking collectively monomer constructing blocks. To make a cloth elastic, the polymer chains are crosslinked by covalent bonds. The extra crosslinks, the shorter the polymer chains and the stiffer the fabric.
“As your polymer chains become shorter, the energy you can store in the material becomes less and the material becomes brittle,” mentioned Junsoo Kim, a graduate student at SEAS and co-first creator of the paper. “If you have only a few crosslinks, the chains are longer, and the material is tough but it’s too squishy to be useful.”
To develop a polymer that’s each stiff and difficult, the researchers seemed to bodily, somewhat than chemical bonds to hyperlink the polymer chains. These bodily bonds, referred to as entanglements, have been recognized within the subject for nearly so long as polymer science has existed, however they have been thought to solely influence stiffness, not toughness.
But the SEAS analysis group discovered that with sufficient entanglements, a polymer may turn into powerful with out compromising stiffness. To create extremely entangled polymers, the researchers used a concentrated monomer precursor resolution with 10 occasions much less water than different polymer recipes.
“By crowding all the monomers into this solution with less water and then polymerizing it, we forced them to be entangled, like tangled strings of yarn,” mentioned Guogao Zhang, a postdoctoral fellow at SEAS and co-first creator the paper. “Just like with knitted fabrics, the polymers maintain their connection with one another by being physically intertwined.”
With a whole bunch of those entanglements, only a handful of chemical crosslinks are required to maintain the polymer secure.
“As elastomers, these polymers have high toughness, strength, and fatigue resistance,” mentioned Meixuanzi Shi, a visiting scholar at SEAS and co-author of the paper. “When the polymers are submerged in water to become hydrogels, they have low friction, and high wear resistance.”
That excessive fatigued resistance and excessive put on resistance will increase the sturdiness and lifespan of the polymers.
“Our research shows that by using entanglements rather than crosslinks, we could decrease the consumption of some plastics by increasing the durability of the materials,” mentioned Zhang.
“We hope that this new understanding of polymer structure will expand opportunities for applications and pave the way for more sustainable, long-lasting polymer materials with these exceptional mechanical properties,” mentioned Kim.
Zhigang Suo, Fracture, fatigue, and friction of polymers wherein entanglements enormously outnumber crosslinks, Science (2021). DOI: 10.1126/science.abg6320
Elastic polymer that’s each stiff and difficult, resolves long-standing quandary (2021, October 7)
retrieved 7 October 2021
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