By Aman, Winter 2022.
As scientists discover new materials that are incredibly strong and light—some even 200 times stronger than steel—the hope grows that such materials can reduce the environmental impact of human activity [1]. Scientists synthesize these supermaterials by arranging molecules and manipulating the materials’ physical properties in novel ways.
One recent discovery concerning polymers illustrates this process. Polymers—until recently—have always been created one-dimensionally, each molecule linking to the next to form chains, the chains being shaped into 3D objects. Our DNA is a polymer; plastics plaguing the oceans are polymers; your woolen socks comprise polymers. They are versatile and cheap, and they make tough, durable, and elastic materials. But tougher polymers might be less elastic, more durable polymers might be less versatile; and polymers both tough and elastic, durable and versatile, like carbon fiber, might be expensive and hard to make. These compromises have often been necessary when dealing with one-dimensional polymers. Now, however, scientists at MIT have discovered the first two-dimensional polymer—forming sheets instead of chains—twice as strong as steel and yet six times lighter [2].
Figure 1: The first 2D polymer, arranged into a sheet [2].
One-dimensional polymers resemble many single wires haphazardly bunched together like a bundle of hay. But this two-dimensional polymer—which the researchers call 2DPA-1—resembles a wired fence (as seen in Figure 1), one strong enough for you to climb over [2]. The polymer’s units are disc-like structures whose chains also bond between each other. The fence is the sheet-like structure 2DPA-1 forms, and these sheets stack together, improving the material’s strength while lowering its density. And the fence is impenetrable: the sheets can even restrict gas from passing through. Indeed, all these qualities come from a simple change in how the molecules arrange themselves. The qualities of super-materials like 2DPA-1 enable a variety of environmental applications.
First, a material like 2DPA-1 would improve the fuel-efficiency of vehicles, since lighter vehicles would need less fuel to travel the same distance, emitting less carbon. Second, that 2DPA-1—and presumably future 2D-polymeric plastics—is mass-producible could reduce the price of everyday goods that use strong and lightweight plastics, such as laptops, phones, water bottles, sporting rackets and clubs, and packaging for fragile goods. And because 2DPA-1 restricts gasses, the material can prevent rust if coated on metal—including the metal in fences, railings, door hinges, taps, pipes, cast iron pans, screws and wrenches, the wheels of your bicycle, and the underside of your car. By extending the longevity of metallic objects, we would need to extract raw materials less, which could reduce the significant carbon emissions the extraction causes today [3].
Aside from plastics, scientists have created ultra-lightweight gels—some even lighter than air—that could have environmental applications such as cleaning oil spills. Graphene aerogel is lighter than air and super elastic: you could compress a cylinder of the gel like you would crush an empty can of Coke, and the gel would return to its original shape [4]. This elasticity allows the gel to significantly, enabling it to absorb 900 times its weight in oil. The gel can be used to clean up oil spills because it doesn’t absorb water. But scientists need to learn how to mass-produce the gel; the process at current is tedious, costly, and energy-consuming. You need carbon nanotubes, graphene oxide, and a machine to chemically remove oxygen from the material. Materials like this gel, then, seem remarkable but are rendered into expensive trinkets if we cannot use them practically. And if such materials are impractical, then they have diminished potential to help the environment.
Helping the environment becomes especially important for conserving nature because scientists can learn from nature’s efficiency when engineering novel materials, making them more practical. Such an opportunity comes from the discovery of the hardest biological material, found in limpets, aquatic snails. Their teeth are stronger than spider silk, which has long been known as the strongest substance made by a living organism [5]. The teeth’s arrangement of the mineral and protein give their strength, so if scientists could weave materials like carbon fiber in similar ways, the fiber could reach its theoretical strength limits. Stronger carbon fiber, then, could mean less of it would provide the same support and reinforcement; less of it would make the machinery lighter and cheaper. And carbon fiber is just one example of how a material could become a super-material by following a biological model.
While super-materials can evolve technology, they can also reverse the damage old technology has caused the environment. Evolving our technology also depends on preserving the environment—illustrating our codependency with nature—through which scientists can discover nature’s own super-materials. Scientists should study them extensively to learn from nature’s intelligence—an intelligence billions of years old.
[1] Sun, Zhuxing, Siyuan Fang, and Yun Hang Hu. 2020. “3D Graphene Materials: From Understanding to Design and Synthesis Control.” Chemical Reviews 120 (18): 10336–453. https://doi.org/10.1021/acs.chemrev.0c00083.
[2] Zeng, Yuwen, Pavlo Gordiichuk, Takeo Ichihara, Ge Zhang, Emil Sandoz-Rosado, Eric D. Wetzel, Jason Tresback, et al. 2022. “Irreversible Synthesis of an Ultrastrong Two-Dimensional Polymeric Material.” Nature 602 (7895): 91–95. https://doi.org/10.1038/s41586-021-04296-3.
[3] Watts, Jonathan. 2019. “Resource Extraction Responsible for Half World’s Carbon Emissions.” The Guardian, March 12, 2019, sec. Environment. https://www.theguardian.com/environment/2019/mar/12/resource-extraction-carbon-emissions-biodiversity-loss.
[4] Hu, Han, Zongbin Zhao, Wubo Wan, Yury Gogotsi, and Jieshan Qiu. 2013. “Ultralight and Highly Compressible Graphene Aerogels.” Advanced Materials 25 (15): 2219–23. https://doi.org/10.1002/adma.201204530.
[5] Barber, Asa H., Dun Lu, and Nicola M. Pugno. 2015. “Extreme Strength Observed in Limpet Teeth.” Journal of The Royal Society Interface 12 (105): 20141326. https://doi.org/10.1098/rsif.2014.1326.