SGER: Flow field quantification in microfluidic mixing systems by single-molecule detection methods

微尺度流体系统广泛应用于生物分析，也出现在燃料电池等能源系统中。这种体系中的雷诺数非常低，因此分子混合增强不能利用湍流效应。相反，有必要应用混沌平流的概念，这在宏观层流中很常见。该SGER将解决被动的、稳定流动的微混合器，尽管一般方法也适用于通过机械驱动产生不稳定流动的主动混合器。有许多旨在产生混沌平流的微混合器设计，这通常是二维（2-D）混沌流动几何对三维（3-D）微通道的适应。从概念上讲，通过将三维通道的连续横切面等同于二维流动中的时间序列来比较流动轨迹，现有的量化微通道流动的努力依赖于单点或现场流速测量，使用微piv等技术。然而，这种测量从根本上与基于二维混沌流类比的流动配置不匹配，因为许多分析混沌流的工具依赖于粒子轨迹（或条纹）的知识，以及它们在低维空间的映射。从速度测量中确定轨迹或条纹线需要了解三维速度场的时间演变，这对于微型piv来说仍然是一个挑战。PI将展示一种在通道型微混合装置中量化流场的新方法，该方法采用单分子检测技术直接测量流条纹。通过允许使用现有的混沌流分析工具，条纹线测量本身比速度场测量更能直接了解混合情况。例如，PI将能够通过考虑初始近端条纹线的散度或固定点的性质等，明确地构建庞加莱截面来评估微通道流动的混沌特性。这些测量最终将为微混合装置的设计和表征提供严格而直观的框架。

CBET-0820745SuMicroscale fluid systems are widespread in bioanalysis, and also appear in energy systems such as fuel cells. Reynolds numbers in such systems are very low, so molecular mixing enhancement cannot exploit turbulent effects. Instead, it is necessary to apply concepts of chaotic advection, which are familiar in macroscale laminar flows. This SGER will address passive, steady-flow micromixers, though the general approach will also be applicable to active mixers that generate unsteady flows through, for example, mechanical actuation. There are numerous micromixer designs that aim to generate chaotic advection, which are often adaptations of two-dimensional (2-D) chaotic flow geometries to three-dimensional (3-D) microchannels. Conceptually, flow trajectories are compared by treating successive transverse sections of 3-D channels equivalently to temporal series in 2-D flows Existing efforts to quantify microchannel flows rely on single-point or field measurements of flow velocities, using techniques such as micro-PIV. Such measurements are fundamentally mismatched with flow configurations based on 2-D chaotic flow analogies, however, because many tools for analyzing chaotic flows rely on knowledge of particle trajectories (or streaklines), and of their mappings into lower-dimensional space. Determining trajectories or streaklines from velocity measurements requires knowledge of the temporal evolution of the 3-D velocity field, which remains challenging for micro-PIV. The PI will demonstrate a new method for quantifying flow fields in channel-type micromixing devices, where the method employs single-molecule detection techniques to measure flow streaklines directly. Streakline measurements inherently offer more direct insight into mixing than velocity field measurements, by allowing access to established tools of chaotic flow analysis. For example, The PI will be able to construct Poincare sections explicitly to assess the chaotic properties of microchannel flows by considering the divergence of initially proximal streaklines, or the properties of fixed points, etc. These measurements will eventually provide a rigorous, yet intuitive framework for the design and characterization of micromixing devices.