Droplet-based Microfluidics as a Versatile Platform for the Determination of Reaction Mechanisms in Nanoscale Systems

纳米材料对新兴应用的潜在影响是巨大的，有可能在替代能源、计算和医学等不同领域产生颠覆性的新技术进步。从分子构建块开始的“自下而上”化学方法是制造纳米级材料的理想途径，因为它们大体上是非常通用的，并且允许设计和合成任意的纳米结构。尽管经过几十年的研究，我们对某些分子实体如何反应形成纳米结构的机理了解甚少。所有影响特定纳米结构形成的变量都使这个问题复杂化，并且不可能先验地设计合成策略。这种经验主义是由于缺乏关于纳米结构成核和生长（各向同性或各向异性）如何受到化学和物理环境影响的原位信息。由固态和材料化学计划支持的提议研究将通过开发迄今为止对纳米结构合成的最彻底的分子水平理解来解决上述问题，该平台利用多功能液滴为基础的微流控平台，可以模拟整体合成过程，并产生难以区分的液滴，其中纳米结构形成反应发生。集成设备将与同步加速器x射线辐射接口，用于现场，实时吸收和散射测量。我们将利用微流控装置来回答关于在球形过渡金属纳米颗粒（NPs）形成过程中，内源/外源阴离子对还原速率和成核生长的影响的基本机制未知，Pt NPs和Au纳米棒的形状控制生长，特别强调捕获诱导各向同性到各向异性转变的初始化学反应。本提案的结果将为开发用于高通量生产任意尺寸、形状和组成的纳米结构的连续反应器提供有价值的信息。该提案的教育推广是为研究生和本科生提供机会，特别是那些来自代表性不足的群体的学生，参与纳米科学、微制造和基于同步加速器的表征的基础研究。据估计，在美国，每100个儿童中就有1个被诊断为自闭症谱系障碍（ASD）。在宾夕法尼亚州的中心县，一个非营利性的人类服务组织，NHS为8-14岁的ASD患者开展了一个课后项目——踏脚石。作为“科学星期二”的一部分，PI和他的小组将率先开发简单且视觉刺激的科学课程。被诊断为ASD的个体是感官学习者，我们的科学课程将主要通过视觉演示来完成，让学生参与，鼓励他们与同龄人、PI和他的研究生进行社会互动。视觉实验涵盖了与所提议的工作相关的概念（包括溶解度、过饱和、成核和晶体学），包括生长冰糖和云的形成。这些课程将被记录下来，并通过YouTube和在宾夕法尼亚州立大学校园每年举行的全国自闭症会议上的现场演示进行传播。

TECHNICAL SUMMARYThe potential impact of nanoscale materials on emerging applications is immense, with the possibility of producing disruptive new technological advances in areas as diverse as alternative energy, computing, and medicine. "Bottom-up" chemical methods that begin with molecular building blocks are ideal routes to nanoscale materials because they, in principal, are extremely versatile and permit the design and synthesis of arbitrary nanostructures. Despite several decades of research, we have very little mechanistic understanding of how certain molecular entities react to form nanostructures. All of the variables contributing to the formation of a particular nanostructure complicate this problem and make it impossible to design synthetic strategies apriori. This empiricism is due to the lack of in-situ information of how nanostructure nucleation and growth (isotropic or anisotropic) is influenced by the chemical and physical environment. The proposed research supported by the Solid State and Materials Chemistry Program will address the problem outlined above by developing the most thorough molecular-level understanding of nanostructure synthesis to date utilizing a versatile droplet-based microfluidic platform that can mimic bulk synthetic procedures and produce indistinguishable droplets within which nanostructure-forming reactions occur. The integrated device will be interfaced with synchrotron x-ray radiation for in-situ, real-time absorption and scattering measurements. We will utilize the microfluidic device to answer fundamental mechanistic unknowns regarding the influence of intrinsic/extrinsic anions on the rate of reduction and nucleation-growth during the formation of spherical transition metal nanoparticles (NPs), shape-controlled growth of Pt NPs and Au nanorods with a particular emphasis on capturing the initial chemical reactions that induce isotropic-to-anisotropic transformation. NON-TECHNICAL SUMMARYThe results of this proposal will provide valuable information to develop continuous reactors for high-throughput production of nanostructures of any arbitrary size, shape and composition. The educational outreach of this proposal is to provide opportunity to graduate students, and undergraduates - especially those from underrepresented groups - to participate in fundamental research in nanoscience, microfabrication and synchrotron-based characterization. It is estimated that 1 in 100 children in the United States have an autism spectrum disorder (ASD) diagnosis. In Centre County, Pennsylvania, a non-profit, human services organization, NHS runs an after-school program - Stepping Stones - for ASD individuals between the ages of 8-14. The PI and his group will take the lead on developing simple and visually stimulating science lessons as part of "Science Tuesdays". Individuals diagnosed with ASD are sensory learners and our science lessons will be primarily accomplished through visual demonstrations enabling student participation which encourages social interaction with their peers, the PI and his graduate students. Visual experiments that cover concepts relevant to the proposed work (including solubility, supersaturation, nucleation and crystallography) include growing rock candy and cloud formation. These lessons will be recorded and disseminated via YouTube and through live demonstrations at the National Autism Conference held annually on the campus of the Pennsylvania State University.