液珠在十字交疊型流道的切割與融合研究

Droplet fission and fusion in cross-overlapping microchannels

張偉軍(Wei-Chun Chang)

指導教授 ： 楊鏡堂 ； 饒達仁

國立清華大學/工學院/奈米工程與微系統研究所/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00347

摘要

本研究發展出創新微液珠操控平台，以簡易之三維十字交疊流道設計操控液珠之切割與融合，數值與實驗分析都驗證本設計能以流率靈活調控子液珠尺寸之功能，也有高效率液珠融合混合並分裂之功能，預期可順利拓展至生醫與化材應用。
本文提出設計理念後，首先分別以理論分析切割和以數值模擬分析融合穩定性後，再以染料實驗觀察分析流體速率對液珠切割及融合行為之影響。在液珠切割部份，通入平台之單股液珠流能在交疊處以調控側向流率來控制分裂子液珠之尺寸。研究先以理論推測液珠之切割機制，將之分為以壓阻力主導的擠斷(squeezing)機制和以剪切力主導的滴出(dripping)機制兩種。進而在實驗中依照液珠尺寸相對於交疊處出口寬度的比例來切換兩種機制，並研究其液珠切割現象之差別。其中僅在滴出模式的操控範圍內，有可調控液珠之尺寸之功能，而液珠之尺寸可小至飛升(femtoliter)尺度。在液珠融合混合部分，通入平台之雙股液珠流能在交疊處快速且穩定地完成融合混合後，分裂為兩顆濃度與尺寸相等之子液珠。研究先從數值模擬歸納出縮減出口寬度能增強剪切力而間接增強液珠流系統的穩定性，因此實驗方面分別設計較窄和較寬兩種出口縮口結構(30, 60 微米)來驗證此論點。結果顯示此兩種設計均偏好在低流率融合，而其融合模式受結構所產生的不同流場影響，分別以追撞(shifted)與對撞(side-by-side)兩種模式融合。其中窄出口設計的表現較佳，除了有較強之剪切力能使每次分裂至兩出口之子液珠尺寸相等外；其融合所呈現的追撞模式具有受相位差影響小之特性，每次分裂之兩子液珠濃度也相等。
本研究之結果將液珠式微流體應用從二維拓展至三維層面，並發展兩種功能：第一，以流率靈活調控子液珠分裂尺寸；第二，整合液珠融合混合並分裂。此兩種功能有多種用途，如切割功能可應用在藥物投放，可調控投放劑量至最小以減少試劑之浪費；而融合混合功能可應用在多產物之生化反應的即時監控上，當改變上游液珠之融合成分時，可從兩出口之子液珠分別同步進行動態檢測來分析特定產物之濃度。

關鍵字

液珠式微流體系統 ； 液珠分裂 ； 液珠融合 ； 液珠操控 ； 可調控液珠分裂

並列摘要

This research developed an innovative droplet microfluidic platform, which is a simple-designed 3-D cross-overlapping microchannel capable of manipulating the fission and fusion of droplets. Numerical simulation and experiments both verified that the platform is able to flexibly control the size of daughter droplets by modulating flow rates, and also fuse, mix, and split droplets in high efficiency. Hence, it is expected to be successfully applied to biomedical technology and chemical materials.
Based on our proposed design concepts, we first examined mechanisms of splitting by theory, analyzed the system stability of fusion and fission through numerical simulation, and then finally observed the effects of distinct flow rates on the behaviors of droplet fission and fusion. In the part of droplet fission, the size of daughter droplets split from single droplet flow can be controlled by adjusting the flow rate from a lateral inlet. To develop this function, we first inferred from theories that two mechanisms were related to this study— squeezing mechanism and dripping mechanism. In the experiment, we switched the two mechanisms by altering the ratio of droplet size and outlet width and investigated how they affected the fission. It was found that only when the platform was operated in the dripping mechanism, daughter droplets, which can be at smallest size of femtoliter, were controllable by adjusting the flow rate. In the part of droplet fusion and mixing, two droplet flows can merge and mix fast and stably in the cross-overlapped region, and then split into two daughter droplets with the same concentration and size at two outlets. This function was developed by first inducing from numerical simulation that reducing the outlet width would enhance the shear stress and then indirectly increased the system stability. Therefore, in the experiment, we designed two outlets with reduced width (30, 60 micrometer). The results showed that droplets favored to be merged at low flow rate in both of the two designs. Besides, due to distinct flow fields produced by the two designs, the merging patterns of them differed: shifted coalescence in the narrow outlet (30 micrometer), and side-by-side coalescence in the wild one (60 micrometer). The narrow outlet performed better than the wild one since its shifted coalescence diminished the influence of phase difference on the fusion, thus enabling two daughter droplets to have the same concentration. In addition, the narrowness of the outlet resulted in stronger shear stress, which helped splitting a mother droplet into two same size daughter droplets.
In summary, this research extended the application of droplet microfluidics from the level of 2-D structure to 3-D structure and developed two functions of it: first, to control the size of daughter droplets by modulating flow rate; second, to integrate the operations of fusion, mixing and fission in a platform. The two aforementioned functions are versatile. For example, the splitting function can be used for reducing the waste of reagents in drug dosing. The function of fusion and mixing can be used to dynamically examine the concentration of specific products in two daughter droplets at the same time.

並列關鍵字

droplet microfluidic ； droplet fission ； droplet fusion ； droplet manipulation ； controllable droplet splitting

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