Measurement of electric double layer thickness appearing on a interface between distilled water and glass by a fluid dynamic method

本研究的主要目的是探索用流体力学方法估算双电层厚度的可能性。在电渗流中，强剪切流在壁面附近占优势，流动阻力产生的热量在壁面附近产生温度分布。通过测量双电层的分布，我们可以估算出双电层的厚度。在这项研究中，(1)对精密测量实验装置进行了改进；(2)研制了高分辨率精密温度计；(3)对温度分布进行了测量。研究结果如下：(1)电渗流通道由两块平行的圆环玻璃板组成，其间隙h可在7μmμh≦80≦m的范围内控制在±0.2μm的精度内，两块玻璃平行放置在0.0016°以内。利用该通道，可以得到与H…一致的流量与外加电压之间的特性关系更多的埃尔姆霍尔特-斯莫卢乔夫斯基理论。电流是体电流和表面电流之和，公式为I=I_B+I_S。这里是通过双电层的电流。到目前为止，这两种电流都无法单独测量。这种新仪器使我们能够第一次单独测量。(2)由于所设计的直径为1μ、长0.5 mm的铂丝微型温度计在水中使用时刚度不足，因此采用了直径为3.1μm的钨丝。电线由涂有薄层清漆(5μm)进行电绝缘。最终达到了0.02℃的温度分辨率和15μm×1 mm的空间分辨率。我们正在开发一种更精确的温度计，考虑到它的硬度和更薄的清漆涂层。(3)测得的通道出口截面的温度分布比墙体参考点上升了约0.5度。这一温升与本研究计划中估计的温升相同数量级，但目前这一测量的不确定度带相当高。为了得到更令人信服的温度分布结果，需要进行更多的技术改进。较少

The main object of this research is to pursue a possibility of estimating the electric double layer thickness by fluid dynamic method. Strong shear flow prevails close to wall in a electroosmotic flow and the heat generation by flow resistance there gives rise to temperature distribution near the wall. By measuring the distribution, we can estimate the thickness of the electric-double layer. In this research program, (1) Revision of a experimental apparatus for precise measurements, (2) Development of high resolution precise thermometer and (3) Measurements of temperature distribution, were made. The results of each study are as follows.(1)An electroosmotic flow channel consists of two parallel donut-glass plates, whose gap h can be controlled within the accuracy of ±0.2μm in the range of 7μ m≦h≦80μm. Two glasses are set parallel to within 0.0016°. Using this channel, the characteristic relation between the flow rate and the applied voltage can be obtained that is consistent with the H … More elmholts-Smoluchowski theory. The electric current is a sum of bulk current and surface current as I=I_B+I_S. Here Is is a current through the electric double layer. Both currents cannot be measured separately so far. This new apparatus enable us to measure Is separately for the first time. The effect of the Joul-heating by Is on the temperature distribution can be estimated in addition to the fluid friction.(2)Because the designed platinum-wire micro thermometer, 1 μ in diameter and 0.5mm in length, has not enough stiffness when used in water, tungsten-wire having 3.1 μm diameter is used. The wire is insulated electrically by coating thin varnish (5μ m). The final performance of the meter are 0.02℃ temperature resolution with 15 μ m × 1mm spatial resolution. We are now developing a more precise thermometer by considering its stiffness and thinner varnish coating.(3)The measured temperature distribution at channel exit section shows about 0.5-degree rise from reference point at the wall. This temperature rise is the same order as that of estimated one in this research program, however, the uncertainty band of this measurement is rather high at this moment. To get more convinced results of the temperature distribution more technical improvements are required. Less