電熱力效應在二維及三維微混合器混合效能之改善

Abstract

近年來，隨著微機電技術的成熟，微流體晶片系統在生醫檢測上的應用也大幅增加。而其中，微混合器即是運用力學機制來加速微流道中不同流體的混合，以提升生醫晶片檢測系統的效率。 在微流道系統中，交流電動力是最常被運用來操控粒子及流體的媒介。交流電動力主要可以分為介電泳、交流電滲，以及電熱力三種。而其效應又隨著溶液中粒子與流體的導電度、介電係數，交流電場的電壓、操作頻率等而有所不同。藉由交流電場的施加，可以達到粒子的收集；或是由渦流的產生，造成流場內的擾動進而提升混合的效果。 本篇論文中，主要在探討電熱力效應的操作下，在二維及三維微混合器中所提昇的混合效率。除了理論的分析討論外，並運用數值模擬軟體，以有限元素法來做模擬的驗證。在主題上，本文主要可以分為三個部分:介電泳於新型微流道的模擬，電熱微混合器，以及直流偏壓操作下之交流電熱混合器。 首先是介電泳的分析，在不同的懸浮粒子與環境流體的介電係數關係下，找出正負介電泳力的跨越頻率，並在銀鏡反應製成的新型微流道中，分別模擬分析出正、負介電泳在此微流道中所產生的效應。此外，將周圍流體帶給粒子的史托克拖曳力(Stokes drag force)也放進模擬分析中討論，探討兩種力共同作用在粒子上所產生的結果。 第二部分則是將電熱效應運用在流體的混合上。以此款新型微流道的幾何設計來改變渦流的位置及形狀，以求混合效率的提升。另外則是在傳統3D 電熱微混合器中，分析流道深度的改變與混合效率間的關係。 最後一個部分在操作的交流電場中加上不同比例的直流偏壓，隨著流道壁面電滲流的效應，增加流場內的擾動而加速混合機制的完成。並嘗試在較少的電極組數下，模擬分析其混合效率的表現。

In recent years, with the rapid development of the micro electro mechanical systems, the "lab-on-a-chip" technique is widely used in the bio-examination. Among the microfluidic systems, a micromixer device is usually utilized for mixing medicines. Via some physical mechanisms, the efficiency of the bio-examination for the micromixer can be accelerated and improved. In microfluidic systems, AC electrokinetics is commonly used as the major tool to manipulate the particles in the suspensions and control fluid motions. AC electrokinetics can be classified into three categories, dielectrophoresis (DEP), AC electroosmosis (ACEO), and electrothermal force (ET). Then, their operating characteristics vary with the permittivity and conductivity of particles and fluids, the magnitude of applied voltage, and the AC frequency. In this study, micromixers are ameliorated in terms of theories and finite element method (FEM). These theories can be divided into three major topics：dielectrophoresis, electrothermal micromixers, and the micromixer driven by DC-biased AC electric field. For dielectrophoresis (DEP), a crossover frequency, which is an AC operating frequency corresponding to positive and negative DEP will be estimated in different characteristics of the particles and surrounding fluids. Furthermore, Physical correlations among them will be investigated by a novel microchannel, which is made by silver mirror reaction. Besides, when the particle behaviors are examined and predicted in terms of simulatiuons, the Stokes drag force contributed by the fluid motion will be also considered except for DEP. For the electrothermal micromixers, the geometrical design of the novel microchannel (2D simulations) will be ameliorated to enhance the mixing efficiency by observing the shape and position of the vortices induced by electrothermal force. On the other hand, a relation between the depth of 3D traditional microchannel and the mixing quality will be calculated and discussed in this part. The last part is the electrothermal micromixer driven by DC-biased AC electric field. Compared with the traditional electrothermal micromixer, with introducing the disturbance of the electroosmotic flow on the microchannel walls, the mixing quality can be enhanced easily, such as few electrode pairs.