Chemical engineers at Massachusetts Institute of Technology (MIT) have created a new material "that is stronger than steel and as light as plastic" by using a novel polymerization process, a process contains relatively small molecules, known as monomers, bring together chemically to produce a very large chainlike or network molecule, called a polymer.

According to MIT, the new material can be easily manufactured in large quantities, stated in its press statement. 

Until now, according to scientists, it was impossible to induce polymers to form 2D sheets. The new material could be used with durable coating for car parts or cell phones, or as a building material for bridges or other structures.

Image © polymer film courtesy of the researchers; Christine Daniloff, MIT.

"New material will be able to be used as a building material for bridges or other structures"

Unlike all other polymers, the new material is a two-dimensional polymer that self-assembles into sheets, which form one-dimensional, spaghetti-like 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," said Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the new 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 added. 

"It has very unusual properties and we’re very excited about that."

The researchers have filed for two patents to be able to generate the material, which they described in a paper appearing in Nature, a leading international weekly journal of science first published in 1869. MIT postdoc Yuwen Zeng is the lead author of the study.

"Polymers, which include all plastics, consist of chains of building blocks called monomers. These chains grow by adding new molecules onto their ends. Once formed, polymers can be shaped into three-dimensional objects, such as water bottles, using injection molding," stated in a press release of MIT. 

"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," the statement added. 

"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," it explained. 

In this new study, Strano and his colleagues formed a new polymerization process "that allows them to generate a two-dimensional sheet called a polyaramide."

The statement explained that "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, stacked on top of each other, are held together by hydrogen bonds between the layers, which proposes a 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 added. 

"This mechanism happens spontaneously in solution, and after we synthesize the material, we can easily spin-coat thin films that are extraordinarily strong."

Due to its self-assembled structure, the new material can be produced in large quantities by simply increasing the quantity of the starting materials. The researchers also 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 said.

The researchers also found that the new material has strong elasticity properties - in which its elasticity is "between four and six times greater than that of bulletproof glass."

Moreover, the "yield strength" of the material is twice than steel, even though the material has only about one-sixth the density of steel, which is relevant to how much force it takes to break the material.

Image courtesy of ISTOCK, JIAN FAN

"It is impermeable to gases"

"The new technique embodies some very creative chemistry to make these bonded 2D polymers," said Matthew Tirrell, dean of the Pritzker School of Molecular Engineering at the University of Chicago.

"An important aspect of these new polymers is that they are readily processable in solution, which will facilitate numerous new applications where high strength to weight ratio is important, such as new composite or diffusion barrier materials," added Tirrell, who was not involved in the study.

Another key feature of the material is that it is impermeable to gases. The statement added that "while other polymers are made from coiled chains with gaps that allow gases to seep through, the new material is made from monomers that lock together like LEGOs, and molecules cannot get between them."

Strano emphasized that "This could allow us to create ultrathin coatings that can completely prevent water or gases from getting through." "This kind of barrier coating could be used to protect metal in cars and other vehicles, or steel structures."

Strano and his students are now studying on the other potential of the material in more detail to see how this particular polymer is able to form 2D sheets. The team are experimenting with changing its molecular makeup to create other types of novel materials.

In February 2021, a Kenyan startup founder Nzambi Matee created a lightweight and low-cost building material that is made of recycled plastic with sand to make bricks that are stronger than concrete material. 

Recently, the DBT unit of ETH Zurich invented a new material, called FoamWork, made of printable mineral foams based on recycled waste, placed in a concrete casting. As stated by ETH Zurich, the resulting mineral composite elements can save up to 70 per cent concrete, are lighter, and feature improved insulation properties.

Top image: detailed view © polymer film courtesy of the researchers; Christine Daniloff, MIT. 

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