液珠式微流體技術因可精確操控液珠的行為及控制液珠，在短時間內形成多個微反應器，被廣泛應用於製藥、化學工程及生物醫學等領域。單乳化液珠於液珠行為與流體參數上已有豐富研究成果，而雙重乳化系統對於其內部流場以及流體參數上之探討仍較缺乏，因此本研究藉由流道控制內部液珠碰撞、融合，探討流體黏度對於內外液珠流場型態的影響以及其融合情形。
本實驗使用兩階段流動聚焦型結構微流道生成雙重乳化液珠，使用微粒子影像測速儀探討內部液珠黏度對於不同流道內部液珠流場變化與碰撞融合行為的影響。於直流道階段，內部液珠受到回流的影響被推向後方，黏度影響內部液珠的移動速度，造成低黏度內部液珠旋轉以及高黏度內部液珠被推向液珠後端；在突縮段階段，高黏度內部液珠速度較低，導致外部液珠在突縮段的拉伸流加速效果較不明顯，而具有低黏度內部液珠的雙重乳化液珠則整體呈現外側高速流動模式；在突擴段階段，由於不同黏度內部液珠在突擴段的加速幅度和液珠旋轉程度不同，擁有兩顆內部液珠的情況下，低黏度內部液珠的變形量較小。突擴段造成內部液珠的碰撞對液珠薄膜的排液效果並不明顯，反而產生反向排液流動對液珠融合產生反效果。根據本研究結果顯示，由於高黏度內部液珠移動速度較慢，在生成後直流道中持續擠壓，使內部液珠實現融合。而低黏度內部液珠在進入突擴段後發生碰撞，於突擴段後直流道中，觀測到融合現象。此實驗結果期望能提供後續雙重乳化系統在實際應用與液珠等行為之參考。

Droplet-based microfluidic is widely used in fields such as pharmaceuticals, chemical engineering, and biomedical sciences due to its ability to control droplet behavior and generate multiple microreactors within a short time. While there is a wealth of research on the behavior and fluid parameters of single-emulsion droplets, studies on the internal flow field and fluid parameters of double-emulsion systems remain relatively few. Therefore, this study explores the effects of fluid viscosity on the flow field changing and related coalescence by controlling the collision and coalescence of internal droplets.
In this study, a two-stage flow-focusing structure was used to generate double-emulsion droplets. Investigate the effects of internal droplet viscosity on the flow field variations and collision-coalescence behavior of droplets in different microchannels by a micro-PIV system. We found that during the straight channel stage, viscosity affects the movement speed of the internal droplets, causing low-viscosity droplets to rotate and high-viscosity droplets to be pushed toward the rear of the droplet. In the convergent section, High-viscosity internal droplets leading to a less pronounced acceleration effect of the stretching flow on the external droplets. During the divergence stage, the acceleration and rotation of internal droplets differ based on viscosity. The drainage flow at the contact surface was not significantly enhanced. Instead, a reverse drainage flow occurs as the droplets recover from deformation. According to the results of this study, due to viscosity affects the movement speed of the internal droplets. Unlike single-emulsion droplets, high viscosity inner droplets in double-emulsion droplets are conducive to coalescence. The experimental results provide a reference for behavior of double emulsion droplets.

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