Researchers on the College of Virginia Faculty of Engineering and Utilized Science have developed a brand new polymer design that seems to rewrite the textbook on polymer engineering. Now not is it dogma that the stiffer a polymeric materials is, the much less stretchable it needs to be.
“We’re addressing a basic problem that has been considered not possible to unravel because the invention of vulcanized rubber in 1839,” mentioned Liheng Cai, an assistant professor of supplies science and engineering, and chemical engineering.
That is when Charles Goodyear unintentionally found that heating pure rubber with sulfur created chemical crosslinks between the strand-like rubber molecules. This crosslinking course of creates a polymer community, reworking the sticky rubber, which melts and flows within the warmth, right into a sturdy, elastic materials.
Ever since, it has been believed that if you wish to make a polymer community materials stiff, you need to sacrifice some stretchability.
That’s, till Cai’s workforce, led by Ph.D. scholar Baiqiang Huang, proved in any other case with their new “foldable bottlebrush polymer networks.” Their work, funded by Cai’s Nationwide Science Basis CAREER Award, is on the quilt of the Nov. 27 challenge of Science Advances.
‘Decoupling’ Stiffness and Stretchiness
“This limitation has held again the event of supplies that have to be each stretchable and stiff, forcing engineers to decide on one property on the expense of the opposite,” Huang mentioned. “Think about, for instance, a coronary heart implant that bends and flexes with every heartbeat however nonetheless lasts for years.”
Huang first-authored the paper with postdoctoral researcher Shifeng Nian and Cai.
Crosslinked polymers are in all places in merchandise we use, from car tires to house home equipment — and they’re more and more utilized in biomaterials and well being care units.
Some purposes the workforce envisions for his or her materials embody prosthetics and medical implants, improved wearable electronics, and “muscle tissues” for gentle robotic programs that must flex, bend and stretch repeatedly.
Stiffness and extensibility — how far a cloth can stretch or increase with out breaking — are linked as a result of they originate from the identical constructing block: the polymer strands related by crosslinks. Historically, the way in which to stiffen a polymer community is so as to add extra crosslinks.
This stiffens the fabric however does not resolve the stiffness-stretchability trade-off. Polymer networks with extra crosslinks are stiffer, however they do not have the identical freedom to deform, and so they break simply when stretched.
“Our workforce realized that by designing foldable bottlebrush polymers that would retailer further size inside their very own construction, we may ‘decouple’ stiffness and extensibility — in different phrases, construct in stretchability with out sacrificing stiffness,” Cai mentioned. “Our method is completely different as a result of it focuses on the molecular design of the community strands moderately than crosslinks.”
How the Foldable Design Works
As a substitute of linear polymer strands, Cai’s construction resembles a bottlebrush — many versatile aspect chains radiating out from a central spine.
Critically, the spine can collapse and increase like an accordion that unfolds because it stretches. When the fabric is pulled, hidden size contained in the polymer uncoils, permitting it to elongate as much as 40 instances greater than normal polymers with out weakening.
In the meantime, the aspect chains decide stiffness, that means that stiffness and stretchability can lastly be managed independently.
It is a “common” technique for polymer networks as a result of the elements that make up the foldable bottlebrush polymer construction are usually not restricted to particular chemical varieties.
For instance, one in all their designs makes use of a polymer for the aspect chains that stays versatile even in chilly temperatures. However utilizing a special artificial polymer, one that’s generally utilized in biomaterial engineering, for the aspect chains can produce a gel that may mimic dwelling tissue.
Like most of the novel supplies developed in Cai’s lab, the foldable bottlebrush polymer is designed to be 3D-printable. That is true even when combined with inorganic nanoparticles, which could be designed to exhibit intricate electrical, magnetic or optical properties.
For instance, they will add conductive nanoparticles, reminiscent of silver or gold nanorods, that are essential to stretchable and wearable electronics.
“These elements give us infinite choices for designing supplies that stability energy and stretchability whereas harnessing the properties of inorganic nanoparticles primarily based on particular necessities,” Cai mentioned.
