Development of micro-PIV for electmosmotic flow measurement

发展了一种新的微流诊断技术“MICRO-PIV”，用于研究微流控装置或系统(如“μTAS”)中由电场力产生的电渗流。微型PIV系统由一个定制的荧光显微镜和几个常规的PIV部件组成，如高灵敏度的制冷CCD摄像机、高功率脉冲激光器、同步器、PC等。利用该光学系统和粒子成像方法，可以方便地对510μm×410μm范围内的任何微细流动进行可视化和高空间分辨率的定量测量。该系统的主要特点是反射式激光照明方式，工作距离远，增加了微型PIV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量的测量，用于测量性能评价。然后，我们测量了电渗…使用Micro-PIV系统获得了更多的c流，并评估了示踪剂颗粒和通道表面的zeta电位对流动的影响。根据PIV和Zeta电位测量的结果，得出了以下考虑因素。首先，微通道内的电渗流除了在壁面附近外，其速度分布是平坦的。其次，即使假设PDMS通道是电中性的，它也会在PDMS通道中产生电渗流。随着示踪粒子的加入，电双电层中的离子密度和电势(包括Zeta电位)也会发生变化，从而导致电渗速度分布的变化。然而，Micro-PIV技术在获得高质量的粒子图像方面存在缺点。通用的Micro-PIV系统利用荧光显微镜对示踪粒子进行成像。为了提高Micro-PIV的离面分辨率，我们提出了一种新型的Micro-PIV技术--共焦Micro-PIV技术。利用这种共焦微型PIV系统，我们可以光学地去除PIV图像中的离焦光，并测量水平横截面上的薄层内的速度分布。作为共焦Micro-PIV的演示，我们测量了小液滴的内部流动，发现了液滴内部的三维流动结构。共焦显微PIV技术为电渗流现象的实验研究提供了一种有效的工具。较少

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