乳化技術在過去數十年間已廣泛於學術研究及產業應用中，乳化液珠在微流通道中傳輸時，兩相流體於液珠界面上的交互作用，流動模式變化快速且複雜，因此本研究利用含有鞘流(sheath flow)流道的微流體晶片，觀測鞘流施加應力於液珠界面時，兩相流體的流動情形。
本研究首先於液珠內流場觀測中，設定生成流率比2.5與5.0，鞘流角度30°與60°，鞘流流率比0、0.5與1.0，探討各流率與鞘流組合和之內部渦旋結構與強度的變化情形；接著，於外部流場設定與內部流場觀測時相同的流場條件，觀測液珠內外兩相之交互作用，最後，使用不同黏度之連續相，觀察不同黏度比結合鞘流角度對於流場之影響。
首先，在黏度比45時，液珠內部渦旋強度隨生成流率比增加而增強，經過鞘流段時，面向鞘流側的渦旋都會因施加外部剪切力使得強度有所增加，而背向鞘流側的渦旋則根據不同角度有不同的影響情形，於30°鞘流角度，環流隨鞘流流率增加而減小；於60°鞘流角度，環流則無太大的變化。根據渦旋結構的變化以及環流與液珠行經鞘流段時的變形量測，本實驗認為液珠變形量將是影響內部渦旋強度的關鍵，另外，渦旋強度增長倍率也隨生成流率比增加而升高。本研究也發現在不同黏度比的情況下，在鞘流階段主導液珠變形的機制也會有所差異，對於往後期望利用流道設計調控液珠內部流動模式的研究團隊，提供初步的流場觀測探討。

Emulsification process has been widely used in both the academic research and industrial applications over the past decades. When the emulsion droplets are transported in the microfluidic channel, the flow patterns of the two-phase fluid are varied and change rapidly on the interface between two phase fluids.
In this study, we used different flow rate ratios between two fluids, different flow rate of sheath flow, and different angles of sheath flow injected to investigate the variation of the internal vortex structure. We also use the continuous phases with different viscosities to observe the combination of the viscous effect and the shear stress effect induced by the sheath flow. When the fluid with higher viscosity used (viscosity ratio between two fluids is 45), the strength of the vortex inside the droplets increase with the increase of the main flow rate. When the droplets passing through the region affected by the sheath flow, the vortex strength of the vortex that near the sheath flow will increase due to the external shear force. In contrast, the strength of the other vortex has a different situation under different injected angles of sheath flow. Based on the change of the vortex structure and the measurement of the related droplets deformation shown in this study, the deformation of the droplets is the key factor of the intensity change of the vortex. In addition, the mechanism that dominates the deformation of the droplets will be different under different viscosity ratios between two fluids. In this study, we provide a significant reference for the further research of droplets manipulation system inside the microchannel.

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