Geometric models of self-assembled particles within volumetric cells and the resulting single-cell occupancy free energy calculations as a function of packing fraction of the hexagonal state (navy blue) and the quasi-diamond state (pink). Credit: David Doan et al.
Materials engineers from Stanford University have developed a 3D nanoprinting method for the production of Archimedean truncated tetrahedrons. The materials created can rapidly shift between states, rearranging the particles to form new geometric patterns.
“A crystal made of nano-ball bearings will arrange themselves differently than a crystal made of nano-dice and these arrangements will produce very different physical properties,” said Wendy Gu, an assistant professor of mechanical engineering at Stanford University. “We’ve used a 3D nanoprinting technique to produce one of the most promising shapes known – Archimedean truncated tetrahedrons. They are micron-scale tetrahedrons with the tips lopped off.”
In the paper, published in Nature Communications, the team nanoprinted tens of thousands of these Archimedean truncated tetrahedrons (ATTs) before stirring them into a solution and observing them self-assembling into various crystalline structures. Most importantly, the materials can shift between states in a matter of minutes by forming new geometric patterns after rearranging the particles.
“If we can learn to control these phase shifts in materials made of these Archimedean truncated tetrahedrons it could lead in many promising engineering directions,” Gu said.
ATTs have long been one of the most desirable geometries for producing materials that can easily change phase. Despite this, their fabrication has been difficult to achieve outside of computer simulations. While others have successfully fabricated these materials, Gu and her team are the first to utilize 3D nanoprinting to achieve it.
“With 3D nanoprinting, we can make almost any shape we want. We can control the particle shape very carefully,” added Gu. “This particular shape has been predicted by simulations to form very interesting structures. When you can pack them together in various ways they produce valuable physical properties.”
Of the many geometric structures possible with the ATTs, the most promising for Gu is a crystalline quasi-diamond structure which is considered the “Holy Grail” within the photonics community.
The team has already begun researching novel applications for the Archimedean truncated tetrahedron nanoparticles which could lead to countless new scientific advancements. “Right now, we’re working on making these particles magnetic to control how they behave,” Gu said. “The possibilities are only beginning to be explored.”