Scientists have created plastic equivalent to steel — strong but not heavy.Plastics, which chemists sometimes call polymers, are a class of long-chain molecules made up of short repeating units called monomers.Unlike previous polymers of the same strength, the new material only comes in membrane form.It is also 50 times more airtight than the most impermeable plastic on the market.Another notable aspect of this polymer is its simplicity of synthesis.The process, which takes place at room temperature, requires only cheap materials, and the polymer can be mass-produced in large sheets that are only nanometers thick.The researchers report their findings Feb. 2 in the journal Nature.
The material in question is called a polyamide, a threaded network of amide molecular units (amides are nitrogen chemical groups attached to oxygen-bonded carbon atoms).Such polymers include Kevlar, a fiber used to make bulletproof vests, and Nomex, a fire-resistant fabric.Like Kevlar, the polyamide molecules in the new material are linked to each other by hydrogen bonds along the entire length of their chains, which enhances the overall strength of the material.
“They stick together like Velcro,” said lead author Michael Strano, an MIT chemical engineer.Tearing materials requires not only breaking individual molecular chains, but also overcoming the giant intermolecular hydrogen bonds that permeate the entire polymer bundle.
In addition, the new polymers can automatically form flakes.This makes the material easy to process, as it can be made into thin films or used as a thin-film surface coating.Traditional polymers tend to grow as linear chains, or repeatedly branch and link in three dimensions, regardless of orientation.But Strano’s polymers grow in a unique way in 2D to form nanosheets.
“Can you aggregate on a piece of paper? It turns out, in most cases, you can’t do it until our work,” Strano said.”So, we found a new mechanism.” In this recent work, his team overcame a hurdle to make this two-dimensional aggregation possible.
The reason polyaramides have a planar structure is that polymer synthesis involves a mechanism called autocatalytic templating: as the polymer lengthens and sticks to the monomer building blocks, the growing polymer network induces subsequent monomers to only Combine in the right direction to strengthen the union of the two.dimensional structure.The researchers demonstrated that they could easily coat the polymer in solution onto wafers to create inch-wide laminates less than 4 nanometers thick.That’s almost one-millionth the thickness of regular office paper.
To quantify the mechanical properties of the polymer material, the researchers measured the force required to poke holes in a suspended sheet of material with a fine needle.This polyamide is indeed stiffer than traditional polymers like nylon, the fabric used to make parachutes.Remarkably, it takes twice as much force to unscrew this super-strong polyamide as steel of the same thickness.According to Strano, the substance can be used as a protective coating on metal surfaces, such as car veneers, or as a filter to purify water.In the latter function, the ideal filter membrane needs to be thin but strong enough to withstand high pressures without leaking small, nuisance contaminants into our final supply – a perfect fit for this polyamide material.
In the future, Strano hopes to extend the polymerization method to different polymers beyond this Kevlar analog.”Polymers are all around us,” he said.”They do everything.” Imagine turning many different kinds of polymers, even exotic ones that can conduct electricity or light, into thin films that can cover a variety of surfaces, he adds.”Because of this new mechanism, maybe other kinds of polymers can now be used,” Stano said.
In a world surrounded by plastics, society has reason to be excited about another new polymer whose mechanical properties are anything but ordinary, Strano said.This aramid is extremely durable, which means we can replace everyday plastics, from paints to bags to food packaging, with fewer and stronger materials.Strano added that from a sustainability standpoint, this super-strong 2D polymer is a step in the right direction to free the world from plastic.
Shi En Kim (as she is usually called Kim) is a Malaysian-born freelance science writer and Popular Science Spring 2022 editorial intern.She has written extensively on topics ranging from the quirky uses of cobwebs—humans or the spiders themselves—to garbage collectors in outer space.
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Post time: May-19-2022