Abstract
Self-assembly of nanocrystals is extensively used to generate superlattices with long-range translational order and atomic crystallographic orientation, i.e. mesocrystals, with emergent mesoscale properties, but the predictability and tunability of the assembly methods are poorly understood. Here, we report how mesocrystals produced by poor-solvent enrichment can be tuned by solvent composition, initial nanocrystal concentration, poor-solvent enrichment rate, and excess surfactant. The crystallographic coherence and mesoscopic order within the mesocrystal were characterized using techniques in real and reciprocal spaces, and superlattice growth was followed in real time by small-angle X-ray scattering. We show that formation of highly ordered superlattices is dominated by the evaporation-driven increase of the solvent polarity and particle concentration, and facilitated by excess surfactant. Poor-solvent enrichment is a versatile nanoparticle assembly method that offers a promising production route with high predictability to modulate and maximize the size and morphology of nanocrystal metamaterials.
Highlights
Self-assembly of nanocrystals is extensively used to generate superlattices with long-range translational order and atomic crystallographic orientation, i.e. mesocrystals, with emergent mesoscale properties, but the predictability and tunability of the assembly methods are poorly understood
The assembly studies were performed on highly purified NCs that had been repeatedly washed in hexane or toluene and 1-pentanol
We have developed and investigated a facile approach based on evaporation-driven poor solvent (PS) enrichment for the growth of mesocrystals with tunable size and/or morphology distribution and degree of order
Summary
Self-assembly of nanocrystals is extensively used to generate superlattices with long-range translational order and atomic crystallographic orientation, i.e. mesocrystals, with emergent mesoscale properties, but the predictability and tunability of the assembly methods are poorly understood. Methods that modulate the particle interactions, by, e.g., an evaporation-driven increase of the particle concentration[14,15,16,17], destabilization by addition of non-solvent[18,19,20], or by application of external fields[21,22], have been used to produce well-ordered superlattices with sizes from hundreds of nanometers to several hundred micrometers. We demonstrate a tunable and robust evaporation-driven, poor-solvent destabilization method for reproducible and predictable assembly of oleate-capped truncated iron oxide nanocubes (NCs) into large and well-ordered superlattices with long-range translational order and atomic crystallographic orientation, known as mesocrystals[29,30]. The tunable evaporation-driven poor-solvent enrichment (EDPSE) assembly method enables predictive production of large and well-ordered nanocrystal superlattices for optoelectronic, magnetic, and biomedical applications
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