毛細幫浦於微流道中傳輸與混合行為之研究：實驗與分析

Investigation of Transport and Mixing in Microchannel Driven by Capillary Pumping：Experiments and Theoretical Analysis

宮春斐(Chun-Fei Kung)

指導教授 ： 朱錦洲 ； 張建成

國立臺灣大學/工學院/應用力學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.02121

摘要

本研究中，成功採取無動力式流體驅動方法以達到混合之目的，而不需要任何外加主動機制，如幫浦、閥門、或外加電動力、電磁力等能量，這些往往會使得整個檢測系統佔據許多空間，因而限制住了微小化與積體化之目的，所以造成許多不便性。然而，表面張力乃唯一的機制可以驅動流體順利進入微流道內。本混合器之流道是無側牆之設計，接著利用底層親疏水間隔以及雙面塗佈疏水材質(鐵氟龍)的玻璃做為流道之上蓋，如此便可以驅動流體順著親水流道區域進入微流道之中。透過理論分析與實驗之比對，在固定流道寬度為100 μm 時，其可找出一最佳流道高度為13 μm，能使得流體僅在表面張力作用下有最大流率約為0.65 nL/sec。對於本混合器而言，最重要的便是要使得兩流體達到完全混合之目的。為此，吾人在流道底部巧妙的置上不對稱交錯式凹槽結構，其可讓兩流體產生螺旋狀三維運動，藉此有效地提高其混合效率。實驗中，流體得以在1.3公分內便能達到完全混合之狀態
同時，此元件亦能應用於血液之驅動，因此吾人首先藉此分析血液在微流道之中流動時，於不同傾斜角下之動態特性。為了節省成本之目的，本流道改採以玻璃底材為主要製程。由實驗中可以發現血液流速在傾斜流道自 （血液往下流動）變化至 （血液往上流動）時，乃呈嚴格遞增之趨勢。此變化趨勢竟然與去離子水的趨勢完全相反。這種獨特的行為可以由吾人所建立出來的動態平衡方程來加以解釋，該方程是由表面力、重力、以及黏滯力以取得平衡。如此可藉由計算黏滯力，並進而推得其對應的有效血容比。發現血容比在血液往下流時因為重力作用會使得紅血球容易堆積於前緣，因而使得黏滯力大大提升，其流速便明顯降低了。
在提升驅動效能的研究方面，吾人考慮利用超疏水介面取代原有的鐵氟龍之設計。吾人利用電感耦合電漿蝕刻法的交互蝕刻機制，並找出最佳之製程參數，藉以成功的在矽晶圓上製備出緻密的矽草結構。該結構可以將去離子水支撐起來，懸浮於矽表面之上，進而達到理想之超疏水介面，其接觸角約為 。同時，在驅動效能測試上，以超疏水介面取代之後，去離子水的平均流速是原有之1.21倍。探究其原因，是由於流體在親水流道中運動時，會與兩側的鐵氟龍疏水介面有所接觸，因而產生摩擦力。然而，對於超疏水介面而言，它可以形成空氣層並隔絕流體，使得親疏水特性更加明顯，如此便能有效的降低來自兩側的摩擦力，進而藉此提升驅動效能。

關鍵字

微流道 ； 表面張力 ； 疏水性 ； 親水性 ； 血容比 ； 血液流速 ； 矽草

並列摘要

In the present study, a power-free method is explored to perform mixing in a microchannel without any external active mechanisms such as pumps, valves or external energies like electrostatic or magnetic fields. Often a relatively large support is needed for the desired power, thus limiting the capability of system miniaturization and integration. The surface tension is the only mechanism for driving the fluids through the microchannel. The channel of this mixer is designed to have no sidewalls with the liquid being confined to flow between a bottom hydrophilic stripe and a fully covered hydrophobic substrate. It is found from theoretical analysis and experiments data that for a given channel width, the flow rate solely due to capillary pumping can be maximized at an optimal channel height. The flow rate is in the order of nanoliters per second, for example, the flow rate is 0.65 nL s−1 at the optimal channel height 13 μm, given the channel width 100 μm. It is most crucial to this power-free mixing device that two liquid species must be well mixed. For this purpose, asymmetric staggered grooved cavities are optimally arranged on the bottom substrate of the channel, which can generate three-dimensional helical recirculation and let two different liquid species mixing efficiently. In the experiment, the fluid can be achieved fully mixing within 1.3 cm.
This device has also been applied to whole blood to analyze the characteristics of blood in a microchannel at different sloping angles. The channel is determined by a bottom hydrophilic stripe on a glass substrate for the purpose of cost effective. It is observed that increasing the sloping angle from (downward flow) to (upward flow) increases the blood flow rate monotonically. The trend of the velocity of blood flow under various sloping angles is totally opposite to that of the DI water. These peculiar behaviors on the micro scale are explained by a dynamic model that establishes the balance among the inertial, surface tension, gravitational, and frictional forces. The frictional force is further related to the effective hematocrit. The model is used to calculate the frictional force from experimental data, and thus the corresponding hematocrit, which is smaller when the blood flows upward.
In order to enhance the driven efficiency of this design, a superhydrophobic surface was considered to replace the original Teflon surface. We can find out the optimal fabrication parameters of utilizing induced couple plasma method, which can successfully generate compact silicon grass on the bottom. This structure can sustain DI water on the grass top and keep the contact angle around . And the average velocity is 1.21 times that of the original design from experimental results. To make a thorough investigation, when fluid flowing in the hydrophilic channel, it may contact with Teflon surface on both sides, thus produce friction force. Nevertheless, as for the superhydrophobic surface, it can form stable air cushion to isolate fluid; therefore, it will effectively reduce the friction force from both sides, and improve the driven efficiency.

並列關鍵字

microchannel ； surface tension ； hydrophobic ； hydrophilic ； blood flow ； silicon grass

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