NSF-DFG Confine: Reacting precursor/solvent microdroplets in confined 2-D microflows for tailored nanomaterials synthesis

This project was awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).Ubiquitously, our daily life involves the use of high surface-area materials. Frequently, these materials are the key to the sustainable use of energy and resources. Examples of their applications include catalytic components, batteries, electrodes, composite materials, gas sensors, flowing agents, 3D printing, and artificial slag systems. The demand for high surface area per unit mass and fast mass transfer in most applications requires using very small particles with a large external surface area. The way to success is by producing and using such nanoparticles, mostly in the form of oxides and often with specific composition, stoichiometry, and multi-material interactions. Their bottom-up synthesis involves reaction, nucleation, surface growth, coagulation, coalescence, and often crystallization. A novel microreactor involving combusting microdroplets is proposed to synthesize nanoparticles of tailored chemical composition and crystal structure in a scalable, uniform, and consistent fashion. Successful results of this project will reveal fundamental processes and improve practical process control to bridge the current gap between laboratory studies and industrial large-scale and high-rate manufacturing of functional flame-synthesized nanoparticles. This project unites the capabilities of researchers from the U.S.A. (Rutgers University) and Germany (University of Bremen), who are recognized specialists in the emerging field of flame synthesis of nanomaterials. Curricula will be developed as an integrated, multidisciplinary research and education project to train a future nano-manufacturing workforce. Through a joint Ph.D./MBA curriculum on technology entrepreneurship, new business ventures based on the IP from this project will be assessed.The proposed program’s objective focuses on investigating the mechanisms of droplet-to-particle conversion (DPC) and gas-to-particle conversion (GPC) in a confined environment by utilizing a reactive multiphase 2D microflow system with controlled individual burning liquid precursor/solvent droplets in precisely adjustable gas composition and temperature environments. Defining 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 other uses. Our microfluidic geometry and available operational parameters allow basic and isolated studies of various phenomena hardly discernable in other macroscopic systems. The microdroplets in the microreactor can experience 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 the same or different precursors. The setup of burning microdroplets moving through a transparent microfluidic reactor (Hele-Shaw cell) 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 modeling will be conducted to understand, optimize, and guide the experiments. Perhaps hitherto unseen in conventional combustion synthesis, the combinations and direct manipulation of uniform droplets in the proposed setup can produce a variety of nanoparticles, such as organic, inorganic, hybrid, and complex nanoparticles, with exceptional control of size, size distribution, morphology, composition, and crystallinity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.