Reacting precursor/solvent microdroplets in confined 2-D microflows for tailored nanomaterials synthesis

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Flame spray pyrolysis (FSP) is a robust technique that can synthesize chemically complex particles via aerosol combustion of precursor/solvent droplets. The burning microdroplets themselves can be regarded as spatially-confined microreactors, with numerous mechanistic pathways involved in realizing the final product size, composition, and morphology. The key idea of our work is to go beyond conventional FSP, and to further confine the burning microdroplets within a Hele-Shaw cell, creating a novel arrangement of microreactors within a microreactor. Such a device not only offers precise fundamental investigation of the variations in chemical properties and physical dynamics for initially same-sized burning droplets affected by confinement in one-dimension, but also affords the definition of the reaction environment with specific parameter histories for single microdroplets to design nanoparticles of tailored chemical composition and crystal structure, in scalable, uniform, and consistent fashion. The objective of the proposed program focuses on investigating the mechanisms of droplet-to-particle conversion and gas-to-particle conversion in a confined environment by utilizing a reactive multiphase 2D microflow system with controlled individual burning liquid precursor/solvent droplets in precisely adjustable environments. Such ability to define process conditions along a microdroplet’s path should allow unparalleled ability to fabricate high-quality and tailored nanoparticles in a continuous system whose output can be directed into another system for inline processing of composite materials or for other uses. The microdroplet reactor can attain large heating and cooling rates, affecting detailed chemistry and transport in far-from-equilibrium conditions. Individual droplet investigation can be conducted using temperature-controlled (heated or cooled) walls to sustain combustion or quench reactions, where the droplets and as-produced nanomaterials can be characterized (e.g., offline using chromatography by sampling) at different locations (correlating to different residence times), thereby measuring reaction kinetics and nanomaterials evolution. Burning droplets can coalesce with burning/non-burning droplets of same or different precursors. The setup is amenable to a host of in-situ diagnostics, including laser-based spectroscopy, high-speed imaging, interferometric particle imaging, and rainbow refractometry. Ex-situ characterization and computational modelling will be conducted to understand, optimize, and guide the experiments. The team of Mädler and Tse have the unique multidisciplinary expertise consisting of combustion, materials synthesis, theoretical and numerical modeling, process engineering, and advanced characterization techniques, along with previous joint work, to address the proposed work.