“We don’t usually think of plastics as being something that you could use to support a building,” says MIT chemical engineer Michael Strano. But a new polymer his team has developed could do that and more.
Unlike all other polymers, which form one-dimensional, spaghetti-like chains of building blocks called monomers, the new material self-assembles into 2D sheets. Scientists have long hypothesized that if polymers could be induced to grow into such a sheet, they should form extremely strong, lightweight materials. Yet many decades of work led to the conclusion that it was impossible. One reason 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 2D structure will be lost.
To create the monomer building blocks, Strano’s lab used a compound called melamine, which contains a ring of carbon and nitrogen atoms, for the monomer building blocks. Under the right conditions, these monomers can grow in two dimensions, forming discs. These discs stack on top of each other, held together by powerful hydrogen bonds between the layers. “This mechanism happens spontaneously in solution,” Strano says, “and after we synthesize the material, we can easily spin-coat thin films that are extraordinarily strong.”
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