Chemical engineers from the Massachusetts Institute of Technology (MIT) in the US have just forged a new material that is as light as plastic and stronger than steel.
It’s the result of a feat thought to be impossible: creating a two-dimensional polymer. All other polymers form long, one-dimensional chains, but this new substance comprises of a polymer that self-assembles into 2D sheets.
According to MIT’s Michael Strano, senior author of the new study in Nature, potential applications include coating car parts or cell phones, or as building material for bridges.
“We don’t usually think of plastics as being something that you could use to support a building, but with this material, you can enable new things,” he says. “It has very unusual properties and we’re very excited about that.”
Wait, what’s a polymer?
A polymer is a class of molecule, made up of repeating units called monomers in a long chain. These grow by adding new monomers onto the end. Some polymers have branches while others are just straight lines, and they can be extremely simple or extraordinarily complex (for example, antibodies or enzymes).
Plastics are all made up of polymers, shaped into 3D objects like food containers or water bottles during manufacturing, by injecting heated polymers into a mould.
As early as 1935, scientists wondered whether polymers could be induced to grow not in a long chain, but a 2D sheet. After years of research, this idea was written off, with scientists concluding that polymers would begin to grow in three dimensions if just a single monomer was added in a different orientation.
But this new study changes the game again.
Strano and colleagues came up with a new polymerisation process that creates 2D sheets called polyaramide. As monomers, they used rings of carbon and nitrogen atoms called melamine, which – under the right conditions in a solution – will grow into 2D discs.
The discs then stack up on top of each other, held fast by hydrogen bonds, to form a strong structure.
“Instead of making a spaghetti-like molecule, we can make a sheet-like molecular plane, where we get molecules to hook themselves together in two dimensions,” Strano explains.
“This mechanism happens spontaneously in solution, and after we synthesise the material, we can easily spin-coat thin films that are extraordinarily strong.”
Plus, the researchers say the material would be easy to manufacture in large quantities because it simply self-assembles in solution.
What can it be used for?
The new material, dubbed 2DPA-1, has several useful properties: it’s twice as hard to break as steel despite being one-sixth less dense, and it’s 4-6 times harder to deform than bulletproof glass.
2DPA-1 is also impermeable to gases, as it’s made up of monomers locked together like Lego bricks, so gas molecules cannot seep between them like they can in polymer chains.
“This could allow us to create ultrathin coatings that can completely prevent water or gases from getting through,” Strano says. “This kind of barrier coating could be used to protect metal in cars and other vehicles, or steel structures.”
The team next aim to fine-tune this material, with the hopes that it will pave the way for a new generation of polymers.