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. Not is it dogma that the stiffer a polymeric materials is, the much less stretchable it must be.
“We’re addressing a basic problem that has been considered not possible to resolve because the invention of vulcanized rubber in 1839,” stated Liheng Cai, an assistant professor of supplies science and engineering, and chemical engineering.
That is when Charles Goodyear by chance 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, it’s a must to sacrifice some stretchability.
That’s, till Cai’s crew, led by Ph.D. pupil 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 duvet of the Nov. 27 concern 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 stated. “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 vehicle tires to residence home equipment — and they’re more and more utilized in biomaterials and well being care gadgets.
Some purposes the crew envisions for his or her materials embrace prosthetics and medical implants, improved wearable electronics, and “muscular tissues” for gentle robotic techniques that must flex, bend and stretch repeatedly.
Stiffness and extensibility — how far a cloth can stretch or develop with out breaking — are linked as a result of they originate from the identical constructing block: the polymer strands related by crosslinks. Historically, the best way to stiffen a polymer community is so as to add extra crosslinks.
This stiffens the fabric however does not remedy the stiffness-stretchability trade-off. Polymer networks with extra crosslinks are stiffer, however they do not have the identical freedom to deform, they usually break simply when stretched.
“Our crew realized that by designing foldable bottlebrush polymers that might retailer further size inside their very own construction, we might ‘decouple’ stiffness and extensibility — in different phrases, construct in stretchability with out sacrificing stiffness,” Cai stated. “Our strategy is totally different as a result of it focuses on the molecular design of the community strands somewhat than crosslinks.”
How the Foldable Design Works
As an alternative 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 develop 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, which means that stiffness and stretchability can lastly be managed independently.
It is a “common” technique for polymer networks as a result of the parts that make up the foldable bottlebrush polymer construction usually are not restricted to particular chemical sorts.
For instance, considered one of their designs makes use of a polymer for the aspect chains that stays versatile even in chilly temperatures. However utilizing a distinct artificial polymer, one that’s generally utilized in biomaterial engineering, for the aspect chains can produce a gel that may mimic dwelling tissue.
Like lots of the novel supplies developed in Cai’s lab, the foldable bottlebrush polymer is designed to be 3D-printable. That is true even when blended with inorganic nanoparticles, which could be designed to exhibit intricate electrical, magnetic or optical properties.
For instance, they’ll add conductive nanoparticles, reminiscent of silver or gold nanorods, that are important to stretchable and wearable electronics.
“These parts give us countless choices for designing supplies that stability energy and stretchability whereas harnessing the properties of inorganic nanoparticles primarily based on particular necessities,” Cai stated.
