Design and Synthesis of Functional Nanostructured Materials via Colloidal Crystallization

Controlling nanomaterial architecture is a versatile way to create materials with tailored properties. Colloidal crystal engineering has emerged as a powerful approach to precisely synthesizing materials with nanoscale architectures. For example, porous crystals are a class of materials with extraordinary properties. Multicomponent crystals provide a promising path forward for the creation of materials with synergistic physical and chemical properties. However, it is still remarkably difficult to synthesize designer multicomponent and porous crystals; moreover, their structure-function relationships remain elusive. Here, we take a materials-by-design approach that takes advantage of programmable DNA interactions to assemble monodispersed nanoparticles of various shapes into (1) multicomponent co-crystals and (2) porous colloidal crystals, each with targeted chemical, optical, or mechanical properties. We further explore the structure-function relationships among these new materials.<br/><br/>To achieve designer multicomponent colloidal crystals, we have developed a series of polyethylene glycol-DNA ligands that enables the co-assembly of polyhedral nanoparticles and spherical nanoparticles into ordered co-crystals. Specifically, polyhedra of different sizes and shapes (e.g., octahedra, tetrahedra, decahedra, and bi-tetrahedra) are co-assembled based on geometry-inspired designs. Furthermore, polyhedral and spherical nanoparticles of different sizes are co-assembled into a series of novel hierarchical structures, where anisotropic nanoparticles are ordered, while spheres are disordered in the lattices. Using these design strategies, we have discovered eight new co-crystals in the DNA-engineered colloidal crystal family. These results highlight the potential of shape-complementarity design strategies for creating new and unusual colloidal co-crystals.<br/><br/>Utilizing our universal synthetic strategy for directing the site-specific growth of anisotropic seeds into exotic nanoparticle shapes and compositions provides a general pathway to design and synthesize an array of metal hollow nanoparticles that are promising building blocks for the assembly of porous colloidal crystals. These hollow nanoparticles, including nanoframes and nanocages, are subsequently assembled using DNA into open channel superlattices with a range of pore shapes and sizes (i.e.,10–1000 nm). We show that the assembly of hollow nanoparticle superlattices is driven by edge-to-edge DNA interactions. The edge-based assembly design rules that emerged from these studies were used to synthesize 12 open channel superlattices with control over crystal symmetry, channel geometry, and topology. We further show that by controlling the geometry and topology of pores, these superlattices can be used for encapsulating and immobilizing guest species within the host open channel structures, and incorporating inorganic or organic guests with spatial specificity into these porous crystals generates a new kind of host-guest structured material. Indeed, the controllable and tunable porosities and periodicities of open channel superlattices make them promising candidates to realize optical phenomena that are not observed in natural materials. For example, the effective refractivity of a porous Au-Pt cubic-close-packed crystal was found to be negative over a wide spectral range (1050–2000 nm). Finally, we found that porous metallic crystals have higher specific strength and stiffness compared to their solid counterparts, which provides new insights into the design and development of materials that are light but strong. These properties of open channel superlattices represent a new class of mechanical metamaterials, due to their porous, low-density structures and diverse crystal topologies. Overall, our work has made important steps toward the rational synthesis of functional co-crystals and porous crystals with significant implications in optics, catalysis, electronics, biology, and mechanics.