From Nano to Macro—Thinking Bigger in Nanoparticle Assembly

The synthesis of ordered superlattices from a metastable colloidal dispersion is easily analogized to the growth of atomic or molecular crystals from a supersaturated solution or vapor, since the products of both processes tend to exhibit similar unit cell symmetries and crystal habits. Indeed, the framework viewing “nanoparticles as atoms” has been incredibly empowering for the ability to synthesize, predict, and even intentionally program colloidal crystal structures. However, as the field continues to advance, it becomes increasingly important to break out of this paradigm, as the inherent size, energy, and timescales involved with colloidal assembly are dramatically different than atomic crystallization. Even if the thermodynamic end products are structurally analogous, the kinetics of their synthetic mechanisms are intrinsically different, and significantly more study is needed to understand the implications of these differences on materials fabrication. Here, we demonstrate nanoparticle self-assembly routes to fabricating free-standing 3D solids of arbitrary macroscopic shapes that can utilize a multitude of different nanoparticle compositions, and also possess specifically programmed nanoscale particle arrangements and controlled microstructure. This talk will outline the key synthesis and processing steps that enable this method of making materials with programmed material structure across ~7 orders of magnitude in length scale, specifically highlighting how the nanoscale nature of the building blocks imparts unique challenges and structural features to the resulting materials.