液滴微流體系統近年來發展迅速，由於它有高通量、高反應速度和液滴操作的重複
性的優點，還能攜帶DNA、蛋白質、細胞及化學藥劑等，使得應用在化學分析和生醫檢測領域上有很大的潛力。本論文以液滴微流體做為微流道的基礎，將被動結合主動式元件，以調控時變電場達到即時地產生微液滴。微尺度下液體的行為表現為層流，不容易分裂成液滴。傳統上微流體多以壓力驅動的方式，藉由流道的幾何設計產生微液滴，但是液滴的尺寸受限於流道尺度，且缺乏精準性和即時地調控。為了改善此限制，本實驗以壓力驅動為被動式元件和氣動式坍塌閥門，加上電場的驅動為主動式元件。壓力驅動簡單亦調節和氣動式坍塌閥門控制流道幾何寬度，將雙相微流體達到tip-streaming 的穩定未產生液滴的模式，此時外加電場即可改變界面形狀，若達到臨界電場時，界面尖端處立即產生微液滴。製程方面利用微機電技術，以PDMS 雙層微結構為晶片基板，並以液態金屬合金EGaIn 作微電極，在低熔點溫度的被感應加熱，並注入微通道，以形成固體電極。本實驗中以不同斜率波形的電場，即時且穩定地產生不同大小之微液珠，在乳化過程是由所施加的壓力和電場，並且非常小液滴體積小於1 femtoliter 可以容易地產生和收集的控制。使用電壓斜波（0 至400V，0.05 秒為單位）跨越的距離施加6 毫米，產生直徑小於1 微米的液滴，即次微液珠。未來期望發展出可產生多樣化樣本且能即時控制微液珠大小之平台，將應用在醫療檢測、生物細胞、化學檢測等相關領域。

This thesis presents an electric-field triggered droplet formation scheme that is capable of producing sub-femtoliter droplets on demand. Pressure-driven flow focusing scheme is enhanced by a time-varying electric field, which acts against interfacial tension and causes the
breakup of droplets. More specifically, Maxwell stress is induced on the interface, where droplets are produced via tip streaming process. PDMS microfluidic devices with embedded solid electrodes are utilized to realize the proposed on-demand droplet formation scheme. In the prototype demonstration, low melting-temperature solder mixed with magnetic nanoparticles is inductively heated and injected into microchannel to form solid electrodes. Meanwhile, a diaphragm is mounted on top of the junction¸ which can be deformed pneumatically to adjust the channel geometries and therefore to control the droplet formation
process. It is demonstrated that the emulsification process is controlled by the applied pressures and electric field, and extremely-small droplets with volumes less than 1 femtoliter can be readily produced and collected. Using a voltage ramp (0 to 400 V in 0.05 seconds)applied across a distance of 6 mm, droplets of diameters less than 1 μm are produced. As such, the demonstrated microfluidic scheme could potentially realize the controllability on the formation of sub-femtoliter droplets, which are desired for a variety of chemical and biological applications.

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