Using an innovative polymerization process, chemical engineers at MIT have developed a new material that is stronger than steel but as lightweight as plastic and is easy to manufacture in large quantities. .
The new material is a two-dimensional polymer that self-assembles into sheets. Unlike all other polymers, which often only polymerize to form long, one-dimensional, spaghetti-like chains, scientists have until now believed that it was impossible to induce polymers to form two-dimensional sheets.
Michael Strano, a professor of chemical engineering at MIT and the main person in charge of this new research work, said that in the past, people usually did not think that plastics could be used as building structural materials, but using this new material, New things can be created. The new material has unusual and exciting properties and could be used as a lightweight, durable coating for car parts or mobile phones, in addition to being used as a building material for bridges or other structures.
The researchers have applied for two patents on the process for generating the material, and the results have been published in a paper in the journal Nature. MIT postdoc Yuwen Zeng is the study's lead author.
Two-dimensional materials
Polymers, including all plastics, are composed of structural units composed of monomers that are repeatedly polymerized into chains. These chains form long chains by continually adding new building blocks to their ends. Once the polymerization process is complete, the polymer can be injection molded to create three-dimensional objects such as water bottles.
There has long been a hypothesis in the materials science community: If polymers could be coaxed to grow into two-dimensional sheets, they should form extremely strong, lightweight materials. But after decades of research in the field, scientists have concluded that such a material is impossible. The important reason is that as long as one monomer rotates upward or downward beyond the two-dimensional plane during the polymerization process, the material will expand and grow in three dimensions, and the sheet-like structure will be lost.
However, in this new study, Strano and his colleagues proposed a new polymerization process that can produce a two-dimensional sheet called polyaramid. The monomer structural unit uses a compound called melamine, which contains a ring of carbon and nitrogen atoms. Under the right conditions, this monomer can grow in two dimensions, forming disc-shaped materials. The discs are stacked on top of each other and held together by hydrogen bonds between the layers, making the structure very stable and strong.
Strano said that the new polymerization process can create sheet-like molecular surfaces instead of creating a long pasta-like molecular chain in the past, so it can automatically connect molecular surfaces on a two-dimensional scale. Together. This polymerization mechanism occurs automatically in solution, and when the material is polymerized, it can be easily spin-coated to form a very strong film.
Because the materials self-assemble in solution, large-scale manufacturing can be achieved by simply increasing the amount of starting materials. The researchers said that this material film can be coated on the surface of other objects, and the material grade is 2DPA-1.
Strano said that with the progress of this scientific research work, mankind has two-dimensional polymers, which will help make it easier to make new materials that are very strong and extremely thin.
Lightweight and high strength
Further studies by the researchers showed that the elastic modulus of the new material - that is, the force required to deform the material - is four to six times higher than bulletproof glass. Additionally, although the material is only one-sixth as dense as steel, its yield strength—the force required to break the material—is twice that of steel.
Matthew Tirrell, dean of the Pritzker School of Molecular Engineering at the University of Chicago, said that this new technology "reflects a very creative chemical approach to making such interconnected two-dimensional polymers."
Tirrell said that an important reason for being able to form this new polymer is that it is easy to generate in solution. Since the material has good specific strength, this will promote many new applications, such as new composite materials. Or membrane materials to prevent diffusion in liquids, etc.
Another key feature of 2DPA-1 is that it is not breathable.
Other polymer materials are typically made of long coiled chains with gaps between molecules that allow gases to seep in. But the new material is made from monomers that fit together like Lego bricks, with gas molecules unable to pass between them.
Using this property, one can create ultra-thin coatings that completely prevent the passage of water or gases. This barrier coating can be used to protect the surfaces of metal structures used in automobiles and other equipment.
The Strano research team is conducting more detailed studies on the mechanism by which this special polymer can form two-dimensional sheets. In addition, researchers are trying to alter the molecular makeup to create other types of new materials.
The research was funded by the Center for Enhanced Nanofluid Transport (CENT), part of the U.S. Department of Energy's Office of Science, and the U.S. Army Research Laboratory. (Chen Jicheng)