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计双电层厚度的可能性。在电渗透流动中，壁面附近存在强剪切流动，壁面附近流动阻力产生的热量引起壁面附近的温度分布。通过测量其分布，我们可以估计出双电层的厚度。本课题主要包括：(1)精密测量实验装置的改进；(2)高分辨率精密温度计的研制；(3)温度分布的测量。各研究结果如下：(1)电渗透流道由两块平行的甜甜圈玻璃板组成，在7μ m≦h≦80μm范围内，其间隙h可控制在±0.2μm的精度范围内。两个玻璃杯平行放置在0.0016°范围内。利用该通道，可以得到与H…More elmholts-Smoluchowski理论相一致的流量与外加电压的特征关系。电流是体积电流和表面电流的总和，I=I_B+I_S。这是通过双电层的电流。到目前为止，这两种电流还不能单独测量。这种新仪器使我们第一次能够单独测量它。除了流体摩擦外，还可以估计出Is的焦耳加热对温度分布的影响。(2)由于所设计的直径为1 μm，长度为0.5mm的铂丝微温度计在水中使用时刚度不足，因此选用了直径为3.1 μm的钨丝。电线用5μ m薄清漆进行绝缘。该仪器的最终性能为温度分辨率为0.02℃，空间分辨率为15 μ m × 1mm。我们现在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)通道出口段实测温度分布较壁面参考点升高约0.5度。该温升与本研究方案中估算温升的数量级相同，但此时该测量的不确定度波段较高。为了得到更令人信服的温度分布结果，还需要进行更多的技术改进。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