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

该项目是通过“密闭空间中的化学和传输（NSF-DFG）”机会获得的，这是一项由美国国家科学基金会和德国科学研究协会（DFG）参与的合作征集。我们的日常生活中无处不在地涉及到高表面积材料的使用。通常，这些材料是可持续利用能源和资源的关键。其应用实例包括催化组件、电池、电极、复合材料、气体传感器、流动剂、3D打印和人工渣系统。在大多数应用中，对单位质量的高表面积和快速传质的需求需要使用具有大外表面积的非常小的颗粒。成功的方法是生产和使用这种纳米粒子，主要以氧化物的形式存在，通常具有特定的成分、化学计量和多材料相互作用。它们自下而上的合成包括反应、成核、表面生长、凝聚、聚结，通常还有结晶。提出了一种新型的微反应器，利用燃烧微滴合成具有特定化学成分和晶体结构的纳米颗粒，并以可伸缩、均匀和一致的方式合成。该项目的成功结果将揭示基本过程并改善实际过程控制，以弥合目前实验室研究与工业大规模和高速率制造功能性火焰合成纳米颗粒之间的差距。该项目联合了来自美国罗格斯大学和德国不来梅大学的研究人员的能力，他们是纳米材料火焰合成这一新兴领域的公认专家。课程将作为一个综合的、多学科的研究和教育项目来开发，以培养未来的纳米制造劳动力。通过技术创业的博士/MBA联合课程，将评估基于该项目知识产权的新企业。该计划的目标是利用反应多相二维微流系统，在精确可调的气体成分和温度环境中控制单个燃烧液体前驱体/溶剂液滴，研究密闭环境中液滴到颗粒转化（DPC）和气体到颗粒转化（GPC）的机制。沿着微滴的路径定义工艺条件应该允许在连续系统中制造高质量和定制的纳米颗粒，其输出可以直接进入另一个系统，用于复合材料的在线加工或其他用途。我们的微流体几何结构和可用的操作参数允许对其他宏观系统中难以识别的各种现象进行基本和孤立的研究。微反应器中的微液滴可以经历较大的加热和冷却速率，在远离平衡状态的条件下影响详细的化学和运输。单个液滴的研究可以使用温度控制（加热或冷却）壁来维持燃烧或淬火反应，其中液滴和作为产生的纳米材料可以在不同的位置（与不同的停留时间相关）进行表征（例如，离线使用取样色谱法），从而测量反应动力学和纳米材料的演变。燃烧液滴可以与相同或不同前体的燃烧/非燃烧液滴结合。燃烧微液滴通过透明微流控反应器（Hele-Shaw cell）的设置适用于许多原位诊断，包括基于激光的光谱学、高速成像、干涉粒子成像和彩虹折射法。将进行非原位表征和计算建模来理解、优化和指导实验。也许迄今为止，在传统的燃烧合成中看不到，在所提出的装置中，均匀液滴的组合和直接操作可以产生各种纳米颗粒，如有机、无机、杂化和复杂纳米颗粒，具有特殊的尺寸、尺寸分布、形态、组成和结晶度控制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.