雙微滴自對準鏡像介電濕潤現象之研究與應用

Abstract

介電濕潤（electrowetting-on-dielectric, EWOD）是一種以施加電壓改變電極上介電 層表面濕潤特性之現象。介電濕潤由於其所耗功率極低，可反覆變化表面疏水性及親 水性，製作簡單且成本低，因此具有其應用與商品化之潛力。並且在微奈米尺度以表 面張力驅動物體，是一種具優勢之方式，因此在未來商品微小化之趨勢下，表面/體積 比增加，如何控制其表面/介面現象極為重要。 雖然介電濕潤已廣泛地應用在生物晶片及顯示元件上，介電濕潤現象研究僅使用固 體電極，並無文獻討論介電濕潤在液體電極上之情形。本實驗室首先開始液體電極之實 驗，由初步實驗及驗證，我們發現三個極為重要的現象：（i）液體電極：當微液滴下方 之固體電極取代為液體電極時，微液滴之介電濕潤現象依然發生。（ii）鏡像介電濕潤： 當液體電極與介電薄膜上之微液滴體積相當時，介電濕潤現象同時再上下兩微液滴上發 生。（iii）雙微滴自對準介電濕潤：此鏡像介電濕潤會將上下兩微液滴自我對準。因此， 我們稱此現象為：「雙微滴自對準鏡像介電濕潤」。本研究之目的為將此特殊之現象作進 一步之研究，並以其特性提出並示範可能之應用。 本研究之目的包括：（a）大體積之液體電極所扮演角色確實與固體電極相同（圖 五）。（b）在固體電極實驗中，介電層中電壓降V 造成之接觸角變化（θ(V)-θ0），在雙 微液滴鏡像介電濕潤中，同樣之電壓降V 確實會造成之兩倍之接觸角變化（上下均同 時發生）。除對此現象之基本瞭解之外，我們也將測試（c）不同之介電薄膜，（d）改 變微液滴之成分，如導電度、DNA、蛋白質、細胞水溶液等，研究其與鏡像介電濕潤 之關係，（e）並改變其填充流體環境，如雙微液滴在油中、雙微氣泡在水（油）中， 以其對此現象更瞭解。在本現象之應用方面，此研究計畫也將設計並製作相關元件及 系統。目前規劃將此現象應用於：（f）雙面凸透鏡、與（g）直接手寫驅動之微液滴生 物晶片平台。

EWOD (Electrowetting-on-dielectric) is a way to change the surface hydrophobicity on top of an electrode. This phenomenon is reversible and consumes very low power. Therefore, it has been widely used in Lab-on-a-Chip, optics, and display applications. Moreover, as we scale down the device, surface tension will be a dominant force. It is vital to understand the surface and interfacial tension in a micro-/nano-scale. Although EWOD has been widely applied, the EWOD phenomenon was mainly studied on dielectric-covered solid electrodes. We made our first attempt to investigate EWOD on a liquid electrode. From the preliminary study, we found three important features. (1) Liquid Electrode: EWOD still occur when replacing solid electrodes with liquid electrodes. (2) Mirror-EWOD: when the size of the liquid electrode is shrunk to a comparable volume of the upper droplet, electrowetting was found on both sides of the dielectric film. (3) Dual Droplet Self-Aligned EWOD: although the original positions of the two droplets are not aligned, when voltage is applied between the probes, the mirror-EWOD force would bring the overlapped droplets to each other. From these observations, we named this phonominon: Dual Droplet Self-Aligned Mirror-EWOD. This project will study the details of the phonominon itself and its applications. The goals of the projects are: (a) Effect of liquid electrodes in comparison to solid electrodes. (b) When applying V, there will be indeed twice the contact angle change in comparison to the solid electrodes case. (c) Effect of difference dielectric films. (d) Bio-fluids droplet testing. (e) Effect of surrounding media. (f) Design of microlens. (g) Investigation of direct handwriting manipulation of droplets.