Drying-induced assembly of colloidal supraparticles from anisotropic nanoparticles

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Colloidal supraparticles made from smaller nanoparticles (NPs) are versatile materials whose properties can be tailored through the chemistry of their constituent NPs and the arrangement of NPs within the supraparticle. Porous supraparticles with significant internal void space are particularly promising for their catalytic, photonic, and physical absorption properties. Such supraparticles can be scalably fabricated using solvent-drying process that assemble NPs inside liquid droplets. These processes are, however, poorly understood because they involve complex molecular thermodynamics and nonequilibrium transport in confinement. This gap in fundamental knowledge limits our ability to engineer supraparticle structures and properties. Prior experiments are largely focused on supraparticles made from spherical NPs, but NPs with interaction or shape anisotropy have untapped potential for realizing new porous supraparticle assemblies. Investigation of these promising strategies is stymied by the formidable space of NP properties and processing conditions that must be explored. There is hence a critical need for accurate and efficient theoretical and computational models that can predict the NP structure inside a drying droplet to engineer new supraparticle materials. The objective of this project is to model and understand the drying-induced assembly of NPs with interaction anisotropy or shape anisotropy into porous colloidal supraparticles. Howard and Nikoubashman will combine their complementary expertise to develop particle-based (Nikoubashman) and continuum (Howard) models for this confined transport process. The particle-based model will use the multiparticle collision dynamics method for modeling hydrodynamic interactions, while the continuum model will use classical dynamic density functional theory. The models will be used to gain fundamental understanding of how confinement effects on NP interactions and dynamics control supraparticle assembly. The collaborative approach will give more insight than would be possible using either approach alone because the two models capture different length & time scales and can guide & validate each other. The models will be applied to study the drying-induced assembly of "patchy" NPs with anisotropic attraction and rod-like NPs with anisotropic shape. The collaborative team will systematically interrogate how NP properties (e.g., number of patches, aspect ratio) and processing conditions (e.g., droplet size, drying rate) determine the porosity distribution in the supraparticle by characterizing local NP density and orientational order. The investigated strategies for modeling supraparticle formation may have impact on society not only through the investigated applications (porous particles for catalysis & photonics), but also in producing tailored nanomedicine therapeutics & diagnostics and in understanding biological function & transport in cells.