- 學位論文
不同表面張力之液珠混合與可調式結構表面操控方法研究
Droplets Mixing with Different Surface Tensions and Droplet-Manipulation on the Tunable Structured-Surface
摘要
本研究主軸有二：一為二顆不同表面張力之微液珠混合研究，提供不同表面張力之工作流體選擇上的參考，使混合更具效率；一為發展可調式結構表面的新式簡單操控方法，以不影響生化液珠本質為前提，提高液珠工作效率。 本研究以蒸氣法於表面上自組裝分子，使表面具有連續梯度而驅動微液珠，以探討微液珠在不同表面張力條件下的碰撞與混合，並利用共軛焦顯微鏡、micro-LIF及微粒子影像測速儀，觀測液珠內部非穩態三維濃度分布與內部流場型態。目前已知微液珠碰撞後結合瞬間會產生巨觀流動，但僅能維持不到300 ms；流動近乎靜止後，液珠混合行為是由擴散而非對流方式所主導。本研究重心為二顆具有不同表面張力大小的液珠之碰撞混合，探討碰撞後所形成的流場及流場對於與混合指標的影響。觀察以微粒子影像測速儀系統計算之速度場，發現表面張力較大者(73.28 mN/m) 碰撞較小者(55.44 mN/m及35.20 mN/m)，於結合瞬間會產生一對稱渦流，使初始混合指標較高；然而表面能差僅影響初始混合指標，接觸面積對總體積的比例和高內聚力流體的位置方為影響混合效率的關鍵。 有鑑於自組裝分子形成的梯度表面或結構表面，用於操控液珠時會受限於傳輸距離及方向，故本研究提出一新式操控方法，結合機械力與奈微結構複合表面，以拉伸方式，融合表面結構梯度傳輸概念及以結構調控可逆潤濕性的想法，同時不傷害液珠本身性質，具有高生物相容性。本研究已證明拉伸具有表面結構的彈性元件，確實得以改變液珠在表面上的親疏水性，繼而將研究重心放在設計製作彈性元件、和可操控彈性元件的穩定定量拉伸裝置，同時設計簡單的量測方法。本研究未來將著眼於各維度的傳輸操控，進一步用於液珠混合反應。 本文研究成果可應用於生化醫學檢測及新藥開發上：在數位微流體系統中，提供不同表面張力之工作流體選擇上的參考，使混合更具效率；而新式操控方式簡單且保持生化液珠本質，未來可用於提高液珠傳輸與混合反應的效率。
並列摘要
This study investigates two topics. The one is droplets mixing with different surface tensions, and these research results could be the reference for working fluids in the digital microsystem. The other one is developing a novel droplet-manipulation method, which enhances the working efficiency of micro-droplets without destruction of biochemical properties. To analyze the droplets mixing behaviors, the coalescence are visualized by a high-speed camera, and the internal flow patterns are resolved by micro-PIV and micro-LIF. Experiments show that a pair of symmetrical vortices droplet happen only when the higher-surface-tension droplet collide the lower one, and hence the initial mixing indices are higher. However, the overall mixing efficiency depends on the ratio of contact area to total volume and the location of the fluid with high cohesion instead of surface energy differences. Transport distances and directions of droplets on the surface with molecular or structured density gradients are limited; therefore, this research proposes a new manipulation method. The method stretches elastic surfaces with hierarchical structures to control structured densities and to generate density gradients, so that droplets alter their wettability and move without change of biochemical properties. This study currently has proved that the novel control concept is practical, and focuses on the design and manufacture of pliable components and stable stretch devices. These results can be applied to biochemical tests and drug developments. The study expects that the mixing investigation is useful to mixing efficiency, and that the new manipulation method will advance droplets’ capability of transport and reacting.