微尺度數位及連續流體之操控及應用

Manipulation and applications of digital and continuous micro fluids

李俊鵬(Chiun-Peng Lee)

指導教授 ： 賴梅鳳

國立清華大學/工學院/奈米工程與微系統研究所/博士(2011年)

摘要

本文欲對數位式電性流體及連續式磁性流體進行操控。在數位式電性流體方面，本文使用單平面及兩平板式介電潤濕法引發液滴共振並對其共振頻進行討論，透過本文提出之雷射掃頻系統量測液滴振盪頻譜，可從中看出液滴發生共振時所對應的驅動頻率。在共振頻實驗數據與理論預測值的比較部份，以單平面式介電潤濕架構驅動液滴振盪時，修正液滴自由液面之曲率半徑可使理論值與實驗值更加符合；當液滴振盪在兩平板式介電潤濕架構下進行時，除了液滴自由液面之曲率半徑外，液滴與固體間的摩擦阻尼及液滴本身長寬比的變化等因素均須被考慮。此外，本文亦首次利用雷射掃頻系統量化出包括液滴反應與驅動電壓間之相位差及液滴接近共振時的拍頻現象。另外本文對液滴共振現象於液滴混合效率提升上的應用性進行實驗驗證，發現當激發出液滴共振時，混合時間能大幅縮短至原本的10%以下，若使液滴在不同共振態間轉換更能將混合時間再度縮短，本文可謂將液滴共振行為應用於混合之首例。 本文也利用液滴充電的原理使電性液滴在直流電極間泳動，並將液滴行為分為四大類，並首次成功對該些行為所對應之電訊號進行量測之研究，不但可透過量測之訊號窺知液滴接觸充電之物理機制，也提出液態電壓轉頻器及混頻器等新穎概念。另外本文也提出以液滴充電現象進行活體細胞傳輸的原型，成功使含有細胞之培養液滴於多個電極間傳輸，並以實驗證明液滴的接觸充電對細胞存活率無明顯影響。在對連續式磁性流體的操控部份，本文提出以微磁性薄膜做為磁力開關的創新設計，利用具有單磁區特性及形狀異向性之微磁性薄膜做為磁場開關之組成元件，並以不同長寬比之菱形磁膜組成一磁場開關，可藉由控制磁膜的磁化方向使該磁場開關產生強弱不同且分明的散場。最後本文以數值模擬的方式驗證磁力開關在微流道系統中之磁流體混合及磁顆粒的分離應用的可能性。

關鍵字

介電潤濕 ； 液滴共振 ； 液滴充電 ； 微混合器 ； 微分離器

並列摘要

The manipulation and applications of digital electric and continuous magneticfluids are investigated in this thesis. For the digital electric fluids, the droplet resonance is excited by both single-plate and two-plates EWOD methods. By usingthe frequency scanning system, amplitude spectrum of an oscillating droplet can be measured, and the resonant frequencies of a droplet then can be figured out. Comparison of the resonant frequencies from theoretical predictions and experimental data is also performed. After modifying the effective curvature radius of droplet free surface, the theoretical predictions can agree with experimental data very well in the single-plane EWOD configuration. While concerning the cases that the droplet is constrained between two plates, factors as the frictional damping comes from the contact of liquid and solid and droplet aspect ratio are needed to be taken into
consideration as well as the free surface curvature to complete the theoretic model. In addition, including the phase spectrum of an oscillating droplet and the beat
phenomenon are also observed by experiment. It is the first time that these phenomenons be quantitatively presented.
Besides, the ability of droplet resonance for enhancing the in-droplet mixing is verified experimentally. If the droplet resonance is excited, the mixing time required to reach 95 % mixing is about only 6.7 % of the mixing time required for the droplet without EWOD actuation. More, when a merged droplet is driven by two alternating driving frequencies, especially alternating resonant frequencies, a well-selected switching time interval of these two frequencies further helps the mixing. The affections of droplet resonance on in-droplet mixing are the first time be verified by this theses.
In addition, the behaviors of a charged water droplet between two DC electrodes are also investigated experimentally. The droplet behaviors can be briefly classified into four categories: low field motion, stable back and forth, unstable bridge, and stable bridge. It is notable that the corresponding electric signals are successfully interpreted in this thesis. Not only the contact charging mechanism can be further understood, a liquid phase electrical converter as a novel applied concept is also associated through these signals. The charged droplet is also used as the cell carrier to transport cells between electrodes, and no obvious influence of the contact charging on cells viability can be found after hundreds times droplet-electrode contact.
For the manipulation of continuous magnetic fluids, a magnetic micromixer and a microseparator integrating patterned magnetic thin films are firstly proposed. Magnetic field switches, which are composed of magnetic films with different aspect ratio, can produce open/closed magnetic flux by controlling the magnetization direction of films. The applications of magnetic switches on micro magnetic fluid mixing and microparticle separation are verified numerically.

並列關鍵字

droplet charging ； droplet resonance ； magnetic micromixer ； magnetic microseparator

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