Forging Nanoparticle Superlattices with Colloidal Metallurgy

Nanoparticle superlattices present transformative opportunities for material design by enabling precise control over both nanoscale organization and composition, however, translating these assemblies into macroscopic constructs while preserving nanoscale order remains a critical challenge due to the incompatibility of traditional processing techniques with colloidal systems. This study introduces "colloidal metallurgy," a framework for understanding and controlling defect evolution and densification in nanoparticle superlattices during colloidal sintering. We investigate the effects of pressure and temperature to elucidate mechanisms of particle transport, defect annealing, and densification as single-crystal colloidal assemblies coalesce into polycrystalline superlattices. Pressure-driven crystallite fracture is identified as the primary mode of densification, while temperature enhances particle mobility, enabling defect reduction and grain growth. A multi-stage sintering strategy employing high temperature annealing to grow grains and restore fracture-based capacity for densification was developed to produce dense (~1% porosity) polycrystals with low defect counts, demonstrating a novel pathway for processing nanoparticle superlattices. By exploring the parallels and distinctions between atomic and colloidal sintering, this work establishes critical insights into the mechanisms governing colloidal material processing. These findings lay the groundwork for defect engineering in colloidal systems, offering a scalable approach to design macroscopic materials with tailored properties.