This new material is a two-dimensional polymer that can self-assemble into sheets. Unlike all other polymers, ordinary polymers can only polymerize to form one-dimensional long chains like spaghetti. So far, scientists have always believed that it is impossible to induce polymers to form two-dimensional sheets.
Michael Strano, a professor of chemical engineering at the Massachusetts Institute of Technology and the principal of this new research work, said that in the past, people usually didn't think that plastics could be used as building structural materials, but using this new material can create new things. This new material has unusual and exciting characteristics, which can be used as a lightweight and durable coating for automobile parts or mobile phones, and also as a building material for bridges or other structures.
Researchers have applied for two patents on the generation process of this material, and related research results have been published in a paper in Nature. Yuwen Zeng, a postdoctoral fellow at MIT, is the main author of this study.
two dimensional material
Polymers, including all plastics, are formed by repeated polymerization of structural units composed of monomers into chains. These chains form long chains by constantly adding new structural units at their ends. Once the polymerization process is completed, the polymer can be made into three-dimensional objects, such as water bottles, by injection molding.
There is a long-standing assumption in materials science that if polymers can be induced to grow into two-dimensional sheets, they should form extremely strong and light materials. However, after decades of research in this field, scientists have come to the conclusion that this material is impossible to realize. The important reason is that as long as one monomer rotates up or down in the polymerization process, beyond the two-dimensional plane, the material will expand and grow in three-dimensional space and lose its flaky structure.
However, in this new study, Strano and his colleagues proposed a new polymerization process, which can produce a two-dimensional sheet called polyaramid. Among them, the monomer structural unit is a compound called melamine, which contains a ring of carbon and nitrogen atoms. Under appropriate conditions, this monomer can grow in two dimensions to form a disk-like material. These disks are stacked on each other and bonded together by interlayer hydrogen bonds, which makes the structure very stable and firm.
Strano said that the new polymerization process can make flaky molecular surfaces instead of long molecular chains like spaghetti in the past, so it can automatically connect molecular surfaces in two dimensions. This polymerization mechanism can occur automatically in solution, and when the material polymerizes, it can easily rotate to form a very strong film.
Because materials can be self-assembled in solution, large-scale production can be realized only by increasing the amount of starting materials. The researchers said that this material film can be coated on other surfaces, and the material brand is 2DPA- 1.
Strano said that with the development of this scientific research, human beings have two-dimensional polymers, which will help to make very strong and thin new materials more easily.
Light weight and high strength
Further research by researchers shows that the elastic modulus of new materials-even the force required for material deformation-is four to six times higher than that of bulletproof glass. In addition, although the density of this material is only one sixth of that of steel, its yield strength-the force required to destroy the material-is twice that of steel.
Matthew Thierer, dean of the Pritzker School of Molecular Engineering at the University of Chicago, said that this new technology "embodies a very creative chemical method to make this interconnected two-dimensional polymer".
Tirrell said that the important reason why this brand-new polymer can be formed is that it is easy to form in solution. Because this material has good specific strength, it will promote many new applications, such as new composite materials or membrane materials to prevent diffusion in liquid.
Another key feature of 2DPA- 1 is that it is airtight. Other polymer materials are usually coiled by long chains, and there are gaps between molecules to allow gas to penetrate. But this new material is made of monomers like Lego bricks, and gas molecules can't pass through it.
Using this feature, people can create an ultra-thin coating that can completely prevent water or gas from passing through. This barrier coating can be used to protect the surface of metal structures used in automobiles and other equipment.
Strano's research team is studying in more detail the mechanism by which this special polymer can form two-dimensional sheets. In addition, researchers are trying to change the molecular composition to create other types of new materials.
This research was funded by the Science Office of the U.S. Department of Energy and the Enhanced Nanofluid Transportation Center (CENT) under the U.S. Army Research Laboratory. (Chen) According to