Development of micro-PIV for electmosmotic flow measurement

为了研究微流体装置或系统（如“μTAS”）中由电磁力产生的电渗透流动，开发了一种新的微流诊断技术“micro- piv”。微型PIV系统由一个定制的聚光荧光显微镜和几个传统的PIV组件，如高灵敏度冷却CCD相机、大功率脉冲激光器、同步器、PC等组成。利用该光学系统和PIV方法，可以实现510 μm x 410 μm范围内的任意微流的可视化和高空间分辨率的定量测量。该系统的主要特点是采用脉冲激光的反射光照明方式和较长的工作距离，这有助于增加微型piv系统的易用性和扩大应用范围。微piv系统已应用于各种微通道流量的测量，用于测量性能评价。在此基础上，利用微piv系统测量了示踪粒子和通道表面的zeta电位对电渗透压流动的影响。以下考虑是由PIV和ζ电位测量的结果得出的。首先，电渗透流在微通道中除靠近壁面外呈现平坦的速度分布。其次，电渗透流在PDMS通道中产生，即使它被认为是电中性的。最后，双电层中的离子密度和电位（包括ζ电位）会随着示踪粒子的增加而变化，从而导致电渗透速度分布的变化。然而，微piv技术在获得高质量的粒子图像方面存在缺点。一般的微piv系统是利用荧光显微镜对示踪粒子成像。因此，微piv图像不仅包含聚焦颗粒的整个荧光投影，也包含未聚焦颗粒的整个荧光投影，这降低了面外测量分辨率。为了提高微piv的面外分辨率，我们开发了一种新的微piv技术——“共聚焦微piv”。利用该共聚焦微PIV系统，我们可以光学地去除PIV图像中的散焦光，并测量水平横截面薄层内的速度分布。作为共聚焦微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。共聚焦微piv技术已被证明是电渗透流动现象实验研究的有力工具。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