數位微液滴操控及共振現象之研究

Digital-micro-fluid manipulation and oscillation behavior

方柏元(HASH(0x1aad34c0))

指導教授 ： 衛榮漢

國立清華大學/工學院/動力機械工程學系/碩士(2008年)

摘要

數位微流體操控目前在生醫晶片及微電子冷卻技術領域近年來已有廣泛的應用，因此對其微流體輸送性能的研究愈顯重要。本研究設計並製作出一介電電濕潤驅動之共平面數位微流體操控系統，對液滴內離子濃度對介電電濕潤現象及自然共振態進行詳細的研究。
實驗結果發現，離子濃度增加對相同電壓下接觸角變化有明顯影響。當液滴內加入弱電解質時，自由離子被驅動電壓吸引至固液界面，造成表面電荷累積量增加使接觸角下降。電解質濃度愈高表面電荷累積量愈大，使相同電壓下的接觸角變化隨濃度提升而增加，接觸角飽和情況也隨濃度增加而延後。但加入強電解質時，因完全解離導致固液界面產生緊密之電荷累積，對驅動電壓形成屏蔽效應，造成接觸角飽和提前。因此在選擇電解液時，濃度及解離率考量均須適當。
本文同時對液滴進行共振行為之研究，以介電電濕潤效應進行驅動，當受力頻率和微液滴之自然共振頻率耦合時，微液滴產生和驅動電壓同調的劇烈周期性運動。研究發現此頻率隨液滴尺寸增大而降低，如能妥善利用此自然現象於增進流體之混合效率上，可設計出低功率、高效能之數位微液滴微混合器。

關鍵字

介電電濕潤 ； 液滴振盪 ； 接觸角

並列摘要

Micro-fluid manipulation has been used extensively in biomedical chips and micro-electro-cooling, so the research in fluid transporting has become more and more important. Based on electro-wetting on dielectric (EWOD) effect, we designed and manufactured a coplanar digital micro-fluidic manipulation system. Using this platform, the nature frequency of droplet and the effect of ionic concentration on the contact angle were tested and explained in detail.
When weak electrolyte is added in the water, Our result shows that increasing of ions enhances the contact angle variation in the same driving potential. A more obvious electric double layer(EDL) compared with water formed near the solid-liquid interface makes a significant contact angle variation and delays the contact angle saturation, which is strongly influenced by the surface charge density. When the weak electrolyte is replaced by strong electrolyte, the stronger charge accumulation shields the driving field, causing the contact angle to saturate earlier. As the result, when electrolytes are used, we have to take concentration and dissociation rate into consideration as far as the contact angle is concerned.
We also investigate the natural frequency shift with droplet size. It becomes higher as the droplet size decreases. When driving frequency couples with the natural frequency of droplet, the irregular and strong vortex due to the violently periodic vibration could be used in fluid mixing.

並列關鍵字

EWOD ； Droplet Oscillation ； Contact Angle

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