This photo might look like a mere product of Photoshop, but it actually is an incredible feat of materials engineering.
Researchers have developed the lightest material ever—about 100 times lighter than Styrofoam [1]! You might be wondering what kind of magical material they discovered that could be so light, but it’s actually just made out of metal. The trick is, it’s only a fraction solid—the other 99.99% is air!
Inspired by the strength of large architectures like bridge supports and the Eiffel Tower,1 collaborators from Boeing’s HRL Laboratories, NASA, and Defense Advanced Research Projects Agency (DARPA) have created a metallic microlattice that is lighter than any other material [1]. This microlattice, which takes established principles of design and shrinks them to the micro scale, is a framework of micro-sized tubes called “struts” arranged to form cells of air pockets.
What makes the microlattice even more special is how strong it is despite weighing so little.2 Other ultra-light materials make use of air, but many are stochastic. Stochastic materials contain randomly spaced air pockets, like aerogels and foams. In contrast, researchers design microlattices with specific patterns of empty space. The patterned cells retain much more strength compared to solid material than random structures do because they can dissipate forces in controlled ways [2].
The microlattice pattern is made using the self-propagating photopolymer waveguide technique, which is a process similar to 3D printing [3]. While the name is a mouthful to say, the technique itself is pretty simple compared to many micro manufacturing processes. First, you create a 3D mold using a material that hardens into a polymer only when hit by UV light. Shining UV light at different angles through a slit mask creates the 3D lattice of polymer. Next, you coat the polymer grid with nickel-phosphorus. Finally, you dissolve the polymer, leaving behind a beautiful network of hollow metal tubes. This relatively easy manufacturing process makes the metallic microlattice even more attractive for scaling up beyond the lab.
Not only is the microlattice extremely light, strong, and easy to construct, but it also has high energy absorption and recovery capabilities. Because each of the struts can move relatively independently, the microlattice can take in large amounts of energy without breaking. This strut flexibility also means that the lattice can be compressed to 50% of its size and bounce back completely reversibly [3]! These properties make the microlattice an ideal candidate for aerospace applications like shock absorbance, where materials need to withstand large impacts and recover to keep doing their job [1]. Furthermore, because flying requires a lot of fuel, lightweight materials are even more important for energy and cost efficiency--which makes the microlattice a winning combination. So just like the metallic microlattice has taken materials engineering to new heights, it might soon do the same for you.
References:
1. Gent, E. Lightest Metal Ever is 99.9 Percent Air. https://www.livescience.com/52973-lightest-metal-ever-is-mostly-air.html (accessed Oct 10, 2018).
2. MacDonald, J. Microlattice: The World’s Lightest Metal. https://daily.jstor.org/microlattice-worlds-lightest-metal/ (accessed Oct 10, 2018).
3. Schaedler, T. A.; Jacobsen, A. J.; Torrents, A.; Sorensen, A. E.; Lian, J.; Greer, J. R.; Valdevit, L.; Carter, W. B. Science 2011, 334(6058), 962–965.
4. HRL Researchers Develop World’s Lightest Material. http://www.hrl.com/news/2011/11/17/hrl-researchers-develop-worlds-lightest-material (accessed Oct 10, 2018).