以一種精確電阻抗法研究電解質溶液低頻的行為

Investigation of Low Frequency Electrolytic Solution Behavior with an Accurate Electrical Impedance Method

何恭竹(Kung-Chu Ho)

指導教授 ： 管傑雄

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201700575

摘要

本論文配合特殊的微流道元件以及高解析度儀器，對單價強電解質溶液操作在低頻下，進行一種精確的電阻抗法；實驗結果顯示比以往電阻抗法較佳的重複性及精確度，尤其在低頻端的部分。此外，實驗數據顯示，電解質濃度愈高，量測準確度愈佳。經由量測實驗數據驗證，電解質行為在低頻即顯現強烈頻散特性；離子在低頻時不僅累積在電極－電解質介面、亦在微流道元件中依電場方向排列。而在較高頻時，週期電場反轉變快，使離子沿電場方向擴散程度減少，因此離子化載子遷移率改善、進而增加傳導機制。對同一電解質而言，濃電解質的較高鬆弛頻率，來自於其較強的極化現象，其起源於較高的電導、即較低的電解質塊材電阻。此外相同濃度下，酸性電解質有最大的電導率，其可歸因於水合離子與水分子間，質子傳輸之額外輔助；此結果在10-4 M以上電解質濃度尤為明顯。更重要的，所有電解質溶液都在介電損耗峰值呈現所謂的鬆弛頻率；此現象與水溶液元件內部總極化鬆弛有關。酸性電解質的鬆弛頻率亦由於質子傳輸輔助大為提升、同時亦使電解質塊材電阻值下降。我們最後以一組二階牛頓運動方程為基礎，先推導出實驗中的水溶液交流電導率，進而用最小平方誤差法求出一組離子遷移率的最佳數值解。我們發現離子遷移率的大小趨勢和傳統文獻高度相關，並在趨近於直流的低頻區、趨勢更為符合；這足以證明本套數學模型預測的準確性，以及未來發展的價值。

本研究預計應用於液體電路元件的研發。我們希望經由此實驗，對離子運動能有進一步了解，謀求研發新型態液體元件之可能，而此元件是可藉頻率調變介電常數的。我們可依此構想設計光閥門、調整出光量不同、進而改變顯示器灰階。此技術若能發展成熟，預計可取代現今液晶技術。

關鍵字

微流道元件 ； 電解質溶液 ； 電阻抗法 ； 質子傳輸 ； 介電損耗 ； 鬆弛頻率 ； 牛頓運動微分方程式 ； 最小平方誤差法

並列摘要

This dissertation reports the investigation of strong univalent electrolytic solutions with a low-frequency electrical impedance method realized through a specific microfluidic device and high resolution instruments. We have shown the better repeatability and accuracy of the proposed impedance method, especially in the lower end of the investigated frequency regime. Moreover, the experimental data shows higher accuracy in the cases of concentrated electrolytic solutions. As verified by the experimentally measured data, the electrolytic behavior reveals strong frequency dispersion relation at low frequencies because dissolved ions not only accumulate at the electrode-electrolyte interface but also align themselves in the microfluidic device along the electric field direction. At higher frequencies, the periodic reversal of the electric field represents so fast that the ions behave less diffuse in the direction of the electric field. Therefore, the improved mobility of ionic carriers is responsible for the conduction mechanism. For the same electrolytic sample, the relaxation frequency of concentrated electrolytes becomes higher owing to the stronger total polarization coming from the higher conductivity as well as the lower resistance in the electrolytes, which is obvious in the concentration above 10-4 M. With the same concentration, the acidic electrolytes represent the highest conductivity, which can be ascribed to the extra assistance of proton transfer mechanism between hydronium ions and water molecules. What’s more, all electrolytic solutions appear the so-called relaxation frequency at each peak value of dielectric loss due to relaxing total polarization inside the solution device. The relaxation frequency of acidic electrolytes also becomes higher because of the proton transfer, which results in the higher conductivity as well as the lower bulk resistance in the acidic electrolytic solutions. Finally, we derived an AC conductivity in the electrolytic solution base on a second-order Newton differential equation of motion, then solved an optimal numerical solution by applying the least square error method (LSEM). We found that the tendency of the frequency-dependent mobility in our experiment is highly correlated to the conventional literatures, especially in the lower end of the frequency, that is, approaching to DC condition, which is sufficient to prove the high potential of predicting ability of the theoretical model.

The results of this dissertation is expected to apply on the liquid circuit device development. We hope to further realize the ion movement from the experiment to seek the possibility of developing novel liquid devices with frequency-tunable dielectric constant. Based on this idea, a novel light valve with tunable amount of light output can be designed. That is, the gray scale can be changed. Then the conventional liquid crystal technology can be entirely replaced if the related technology has been well-developed.

並列關鍵字

microfluidic device ； electrolytic solution ； electrical impedance method ； proton transfer ； dielectric loss ； relaxation frequency ； Newton differential equation of motion ； least square error method

參考文獻

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