In a outstanding feat of chemistry, a Northwestern College-led analysis staff has developed the primary two-dimensional (2D) mechanically interlocked materials.
Resembling the interlocking hyperlinks in chainmail, the nanoscale materials reveals distinctive flexibility and energy. With additional work, it holds promise to be used in high-performance, lightweight physique armor and different makes use of that demand light-weight, versatile and difficult supplies.
Publishing on Friday (Jan. 17) within the journal Science, the examine marks a number of firsts for the sector. Not solely is it the primary 2D mechanically interlocked polymer, however the novel materials additionally comprises 100 trillion mechanical bonds per 1 sq. centimeter — the very best density of mechanical bonds ever achieved. The researchers produced this materials utilizing a brand new, extremely environment friendly and scalable polymerization course of.
“We made a very new polymer construction,” mentioned Northwestern’s William Dichtel, the examine’s corresponding creator. “It is much like chainmail in that it can’t simply rip as a result of every of the mechanical bonds has a little bit of freedom to slip round. When you pull it, it might dissipate the utilized power in a number of instructions. And if you wish to rip it aside, you would need to break it in lots of, many alternative locations. We’re persevering with to discover its properties and can most likely be finding out it for years.”
Dichtel is the Robert L. Letsinger Professor of Chemistry on the Weinberg School of Arts and Sciences and a member of the Worldwide Institute of Nanotechnology (IIN) and the Paula M. Trienens Institute for Sustainability and Power. Madison Bardot, a Ph.D. candidate in Dichtel’s laboratory and IIN Ryan Fellow, is the examine’s first creator.
Inventing a brand new course of
For years, researchers have tried to develop mechanically interlocked molecules with polymers however discovered it close to not possible to coax polymers to kind mechanical bonds.
To beat this problem, Dichtel’s staff took a complete new strategy. They began with X-shaped monomers — that are the constructing blocks of polymers — and organized them into a selected, extremely ordered crystalline construction. Then, they reacted these crystals with one other molecule to create bonds between the molecules inside the crystal.
“I give a variety of credit score to Madison as a result of she got here up with this idea for forming the mechanically interlocked polymer,” Dichtel mentioned. “It was a high-risk, high-reward concept the place we needed to query our assumptions about what varieties of reactions are attainable in molecular crystals.”
The ensuing crystals comprise layers and layers of 2D interlocked polymer sheets. Throughout the polymer sheets, the ends of the X-shaped monomers are bonded to the ends of different X-shaped monomers. Then, extra monomers are threaded by means of the gaps in between. Regardless of its inflexible construction, the polymer is surprisingly versatile. Dichtel’s staff additionally discovered that dissolving the polymer in answer prompted the layers of interlocked monomers to peel off one another.
“After the polymer is fashioned, there’s not a complete lot holding the construction collectively,” Dichtel mentioned. “So, once we put it in solvent, the crystal dissolves, however every 2D layer holds collectively. We will manipulate these particular person sheets.”
To look at the construction on the nanoscale, collaborators at Cornell College, led by Professor David Muller, used cutting-edge electron microscopy methods. The pictures revealed the polymer’s excessive diploma of crystallinity, confirmed its interlocked construction and indicated its excessive flexibility.
Dichtel’s staff additionally discovered the brand new materials could be produced in giant portions. Earlier polymers containing mechanical bonds sometimes have been ready in very small portions utilizing strategies which can be unlikely to be scalable. Dichtel’s staff, then again, made half a kilogram of their new materials and assume even bigger quantities are attainable as their most promising functions emerge.
Including energy to robust polymers
Impressed by the fabric’s inherent energy, Dichtel’s collaborators at Duke College, led by Professor Matthew Becker, added it to Ultem. In the identical household as Kevlar, Ultem is an extremely robust materials that may stand up to excessive temperatures in addition to acidic and caustic chemical substances. The researchers developed a composite materials of 97.5% Ultem fiber and simply 2.5% of the 2D polymer. That small proportion dramatically elevated Ultem’s total energy and toughness.
Dichtel envisions his group’s new polymer might need a future as a specialty materials for lightweight physique armor and ballistic materials.
“We’ve much more evaluation to do, however we will inform that it improves the energy of those composite supplies,” Dichtel mentioned. “Virtually each property now we have measured has been distinctive indirectly.”
Steeped in Northwestern historical past
The authors devoted the paper to the reminiscence of former Northwestern chemist Sir Fraser Stoddart, who launched the idea of mechanical bonds within the Nineteen Eighties. Finally, he elaborated these bonds into molecular machines that change, rotate, contract and broaden in controllable methods. Stoddart, who handed away final month, obtained the 2016 Nobel Prize in Chemistry for this work.
“Molecules do not simply thread themselves by means of one another on their very own, so Fraser developed ingenious methods to template interlocked buildings,” mentioned Dichtel, who was a postdoctoral researcher in Stoddart’s lab at UCLA. “However even these strategies have stopped in need of being sensible sufficient to make use of in large molecules like polymers. In our current work, the molecules are held firmly in place in a crystal, which templates the formation of a mechanical bond round each.
“So, these mechanical bonds have deep custom at Northwestern, and we’re excited to discover their prospects in ways in which haven’t but been attainable.”
The examine, “Mechanically interlocked two-dimensional polymers,” was primarily supported by the Protection Superior Analysis Initiatives Company (contract quantity HR00112320041) and Northwestern’s IIN (Ryan Fellows Program).
