Nanoparticle lattices stack up in solids

Nanoparticles, because of their size, can give materials interesting properties, such as unusual mechanical and optical features. But scientists have had a tough time taking organized nanoparticles and making them into macroscale materials. They’ve been able to make only thin coatings or micrometer-sized crystallites out of nanoparticle lattices—until now. Chemists at the Massachusetts Institute of Technology led by Robert J. Macfarlane have created centimeter-scale solids composed of organized nanoparticle lattices (Nature 2021, DOI: 10.1038/s41586-021-03355-z). The solids could find use as protective casings or as optical or magnetic metamaterials for display, sensing, and data storage technologies. The chemists make the solids by coating gold nanoparticles with polystyrene brushes. The brushes’ tips are modified with either diaminopyridine or thymine, which are able to form hydrogen bonds to one another, thereby controlling the nanoparticle assembly (shown). The researchers then centrifuge a slurry of the nanoparticles and squeeze them into molds to make the solids. “That processing step is something that we don’t always think about as chemists if we focus on just the molecular structures,” Macfarlane says. “Having the material isn’t enough—you have to be able to put it in the right form.”