Development of micro-PIV for electmosmotic flow measurement

为了研究微流控装置或系统（如μTAS）中的电渗流，发展了一种新的微流控诊断技术--微粒子图像测速技术（micro-PIV）。微型PIV系统由一台自制的落射荧光显微镜和高灵敏度的冷CCD摄像机、高功率脉冲激光器、同步器、PC机等常规PIV组件组成，利用该光学系统和PIV方法，可以方便地对510 μm × 410 μm范围内的微流场进行高空间分辨率的可视化和定量测量。该系统的主要特点是采用聚光反射光照明方式，工作距离远，提高了系统的易用性，扩大了系统的应用范围，并已应用于各种微通道流场的测量，对测量性能进行了评价。然后，我们测量了 ...更多信息 c流动的微型PIV系统，并评估了zeta电位的示踪粒子和通道表面上的流动的影响。以下考虑来自PIV和zeta电位测量的结果。首先，电渗流在微通道中除了壁面附近外，速度分布是平坦的。其次，电渗流出现在PDMS通道，即使它被假定为电中性。最后，双电层中的离子密度和电势（包括ζ电势）根据额外的示踪剂颗粒而变化，这导致电渗速度分布的变化。然而，微PIV技术在获得良好质量的粒子图像方面具有缺点。一般的显微PIV系统利用落射荧光显微镜对示踪粒子进行成像。为了提高显微PIV的离面分辨率，我们发展了一种新的显微PIV技术--共焦显微PIV。利用该共焦显微PIV系统，我们可以从PIV图像中光学地去除散焦光，并测量水平截面上薄层内的速度分布。作为共焦显微PIV的演示，我们对小液滴的内部流动进行了测量，得到了液滴内部的三维流动结构。共焦显微PIV技术是研究电渗流现象的有效工具。少

A new micro flow diagnostic technique, "micro-PIV", has been developed in order to investigate the electroosmotic flow, which is generated by electrical force in microfluidic devices or systems such as "μTAS". The micro-PIV system consists of a custom-built epifluorescent microscope and several conventional PIV components such as a high-sensitive cooled CCD camera, a high-power pursed laser, synchronizer, PC and so on. Using this optical system and PIV method, any micro flows in the fields of 510 μm x 410 μm can be visualized readily and measured quantitatively with high-spatial resolution. The key features of the present system are reflected-light illumination method with pursed lasers and long working distance, which help to increase the ease of use and expand the application range of the micro-PIV system.The micro-PIV system has been applied to the measurement of various microchannel flows for the purpose of measurement performance evaluation. And then, we measured the electroosmoti … More c flow using the micro-PIV system and evaluated the effects of zeta-potential of both tracer particles and channel surfaces on the flow. The following considerations are derived from the results of PIV and zeta-potential measurements. Firstly, electroosmotic flow in a microchannel shows flat velocity profiles except near the wall. Secondly, electroosmotic flow arises in a PDMS channel even though it assumed to be electrically neutral. Finally, the ion density and the potential (including zeta-potential) in the electrical double layer vary according to additional tracer particles, which leads to changes in electroosmotic velocity profiles. The micro-PIV technique, however, has a disadvantage in obtaining a good quality of particle images. The general micro-PIV system makes use of the epifluorescent microscopy so as to image the tracer particles. Therefore, the micro-PIV images always include projection of whole fluorescent light from not only the focused particles but also the unfocused particles, which decreases the out-of-plane measurement resolution.In order to improve the out-of-plane resolution of micro-PIV, we have developed a new micro-PIV technique, "confocal micro-PIV". Using this confocal micro-PIV system, we can remove the out-of-focus light optically from PIV images and measure velocity distributions within a thin layer of a horizontal cross-sectional plane. As the demonstration of confocal micro-PIV, we have measured the internal flow of the small droplet, and found out three-dimensional flow structure inside the droplet. The confocal micro-PIV technique has proved to be a useful and powerful tool for the experimental study of the electroosmotic flow phenomenon. Less