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讨用流体动力学方法估算双电层厚度的可能性。电渗流中，壁面附近存在强烈的剪切流动，流动阻力产生的热量引起壁面附近的温度分布。通过测量这种分布，我们可以估算出双电层的厚度。在本研究计划中，（1）修改了精密测量的实验装置，（2）开发了高分辨率精密温度计，（3）测量了温度分布。每项研究的结果如下。(1)An电渗流通道由两块平行的环形玻璃板组成，其间隙h在7μ m ~ 80μm范围内可控制在±0.2μm以内。两个玻璃杯平行放置，在0.0016°范围内。利用该通道，可以获得与H ...更多信息 elmholts-Smoluchowski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Is是通过双电层的电流。到目前为止，这两种电流都不能单独测量。这种新装置使我们能够第一次单独测量Is。除了流体摩擦之外，还可以估计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 μ m、长度为0.5mm的铂丝微型温度计在水中使用时刚度不够，所以采用了直径为3.1 μm的钨丝。电线通过涂覆薄清漆（5μ m）进行电绝缘。该仪器的温度分辨率为0.02℃，空间分辨率为15 μ m × 1 mm。我们正在开发一种更精确的温度计，考虑到它的刚度和更薄的清漆涂层。（3）通道出口截面的实测温度分布表明，相对于壁面参考点约有0.5 °的温升。该温升与本研究计划中估计的温升数量级相同，但目前该测量的不确定度带相当高。为了得到更可信的温度分布结果，需要更多的技术改进。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