本研究目的為液滴分裂機制之探討，上游端利用流體聚焦技術(flow focusing technique)產生母液滴，再利用由下游端不對稱之分岔(bifurcation)微流道設計將液滴分裂成不同大小的子液滴，探討不同分岔角度及子流道流阻比下對液滴產生及分裂所造成的影響。
研究中液滴分裂器之分岔角度共有30°、60°及180°三種不同變化，流阻比R1/R2共有0.1、0.3、0.5、0.71四種變化。當流阻比為R1/R2=0.1及R1/R2= 0.3時，由於子流道內流率比 過大，導致液滴未被分裂直接流入子流道1內。當流阻比為R1/R2=0.5，Qc/Qd由0.8 ml/min變化至2.8 ml/min時，分岔角度為60°之液滴分裂器所分裂之子液滴投影面積比A1/A2最大，30°時次之，180°時所分裂之A1/A2最小。但流阻比為R1/R2=0.71時，A1/A2隨分岔角度增加而變小。對於R1/R2=0.5及R1/R2=0.71兩種流阻比，在固定Qc/Qd時，分岔角度為180°所分裂之子液滴投影面積比A1/A2皆為最小，這是因為分岔角度為180°時，子流道流率比 最小，造成剪應變率比 較小，進而導致子液滴分裂之投影面積比A1/A2在不同流阻變化下皆為最小。
由uPIV之分析可知，分岔角度為30°及60°時，受到子流道1內較大之體積流率的影響，導致分裂過程中液滴內靠近子流道2的相對速度皆朝向子流道1之方向流動。反之，分岔角度為180°時，由於分裂區母流道與兩子流道皆呈90°彎角，使液滴進入分裂區時，近似遇到一檔體，造成母液滴前端流速減速，使其相對而言朝液滴行進之反方向(-x方向)流動，與液滴後端之正向(x方向)相對速度在液滴中央處形成一鞍點 (saddle point)。

This study aims at exploring the different mechanism during droplet fission in a bifurcating microfluidic. First, flow focusing technique is utilized to generate droplets, Then, an asymmetric bifurcation devices fission droplets into daughter-droplets with different sizes. In order to accurately control the proportion of splitted droplets, two key parameters, bifurcation angle and the flow resistance ratio of two daughter channels are considered. Three bifurcation angle (30°, 60°, 180°) and four flow resistance ratio (R1/R2 = 0.1, 0.3, 0.5, 0.71) are tested.
When R1/R2 = 0.1 and 0.3, the flow rate ratio in daughter channels becomes too large such that incoming droplets pass though the wider daughter channel without fission. As R1/R2 increases to 0.5, the ratio of daughter-droplet projection area A1/A2 peaks with a bifurcation angle of 60°, following by a bifurcation angle of 30°, and a bifurcation angle of 180° produces minimal A1/A2. In contrast, A1/A2 decreases with the increase of bifurcation angles for R1/R2 = 0.71. Hence, A1/A2 reaches minimum with a bifurcation angle of 180°for R1/R2 = 0.5 and 0.71. This is because a bifurcation angle of 180° results in small ,and the corresponding strain rate ratio produces the lowest A1/A2 consequently.
For 30° and汹60°, the 贡PIV analysis reveal that relatively fluid near the front of end of droplet move toward the wider daughter channel due to large inertia force. For 180°, on the contrary, there exists a saddle point in droplets because the 180° bifurcation forms an obstacle for the incoming droplets, causing a relative reverse flow near the front.

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