Scientists have believed it’s impossible to induce polymers to form 2D sheets, but using a novel polymerization process, MIT chemical engineers have created a new material that is stronger than steel, as light as plastic, and it can be easily manufactured in large quantities.
According to press information from MIT, the material is a two-dimensional polymer that self-assembles into sheets, unlike all other polymers, which form one-dimensional chains. Such a material could be used as a lightweight, durable coating for car parts or cell phones, or as a building material for bridges or other structures, says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the study.
“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.
Polymer scientists have long hypothesized that if polymers could be induced to grow into a two-dimensional sheet, they should form extremely strong, lightweight materials. However, many decades of work in this field led to the conclusion that it was impossible to create such sheets. One reason for this was that if just one monomer rotates up or down, out of the plane of the growing sheet, the material will begin expanding in three dimensions and the sheet-like structure will be lost.
However, Strano and his colleagues developed a new polymerization process that allows them to generate a two-dimensional sheet called a polyaramide. For the monomer building blocks, they use a compound called melamine, which contains a ring of carbon and nitrogen atoms. Under the right conditions, these monomers can grow in two dimensions, forming disks. These disks stack on top of each other, held together by hydrogen bonds between the layers, which make the structure very stable and strong.
“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 says. “This mechanism happens spontaneously in solution, and after we synthesize the material, we can easily spin-coat thin films that are extraordinarily strong.”
Because the material self-assembles in solution, it can be made in large quantities by simply increasing the quantity of the starting materials. The researchers showed that they could coat surfaces with films of the material, which they call 2DPA-1.
“With this advance, we have planar molecules that are going to be much easier to fashion into a very strong, but extremely thin material,” Strano says.
The research was funded by the Center for Enhanced Nanofluidic Transport (CENT), an Energy Frontier Research Center sponsored by the U.S. Dept. of Energy Office of Science, and the Army Research Laboratory.
The researchers have filed for two patents on the process they used to generate the material, which they describe in a paper published in Nature.