應用共軛焦顯微術及微PIV分析微液珠於複合表面之碰撞與混合

Abstract

本研究旨在探討奈微複合結構表面上的多組份微液珠碰撞與混合，透過自組裝分子以蒸鍍法使複合表面具有特定梯度，並驅動微液珠從疏水端移動到親水端碰撞同樣體積及組份之靜止液珠，進行混合。本文利用共軛焦顯微鏡及微粒子影像測速儀系統量測液珠內部非穩態三維濃度分布與內部流場型態，並可得知黏滯性的上升以及表面張力的下降將減少表面輪廓震盪時間。從無因次參數Peclect數可知，微液珠結合瞬間內部流場以對流為主導的時間不到300 ms，混合行為主要是以流場靜止後的擴散為主。依據Stokes-Einstein relation以及實驗可知，擴散係數僅與黏滯性有關，與表面張力較無關聯性，故混合指標與黏滯性的高低成反比關係；又因表面張力的下降使液珠結合不完全，也使混合指標隨之下降。 微液珠在碰撞結合瞬間由於表面能差轉換為碰撞時的動能，會有部分能量在內部造成對流質傳以及擴散質傳的現象，剩餘表面能則造成表面輪廓震盪。實驗藉由高速攝影機擷取影像並計算震盪時間，判斷微液珠內部質點混合後的分布機率，並定量出微液珠內部的速度場以及渦度場大小。由無因次參數Webber number,Collision parameter可以看出碰撞行為屬於coalescence，而從Peclect number可知速度場大小與對流行為成正比關係，但在微尺度下微液珠動能極小，對流主導時間短，故對於混合效率並無顯著影響，主要以擴散為主。混合指標的計算為利用雷射激發螢光DNA (FAM and Cy5)，再以螢光強度來定量出指標數值，並利用3D重建剖面技術來觀察混合瞬間的染料分布情況，以瞭解兩微液珠間碰撞結合靜止後經由對流所形成的流場趨勢。 本研究結果將於生化領域以及燃油的噴射燃燒方面有所貢獻。在不同組份的微液珠混合分析下，找出提高傳輸速率以及混合效率的最佳比例，也對於爾後進行生物液珠攜帶檢體試劑的混合以及燃油噴射燃燒前時油滴的碰撞行為提供良好的參考依據，並期望液珠混合技術在各領域的發展應用能有更佳的創新與突破。

This study investigates the phenomenon of head-on collisions between a moving droplet and stagnation droplet by self-assembled monolayer method. At this research, we utilized experiment analysis to observe the characteristics of flow field during the transport and mixing process by varying the property of viscosity and surface tension. The coalescence dynamic are visualized by a high-speed camera; while the internal flow patterns are resolved by micro-PIV and micro-LIF. Surface energy transformed to kinematic energy before the coalescence between two droplets, remnant energy will cause oscillation on the contour. According to Webber number, Collision parameter, and Peclect number we found that the behavior of collision mode is permanent coalescence and convective intensity is proportional to velocity field. By scaling law, we know that convection is not the main dominate parameter but diffusion while mixing. For quantify the mixing mechanisms, we used fluorescent dye to define the mixing index that provided the mixing behavior within a droplet after collision. The contribution of this study is the application of textured surface and provided more data of biochemical fluid. Most important of all, we established a way to visualize into the droplet.