| 摘要: | 熱毛細現象是由於液體內部存在溫度差異時，使表面張力形成梯度分布，進而產生特定方向的牽引力。這種現象能夠作為液體傳輸的一種驅動力。在過往的研究中，單以熱毛細力驅動液珠，雖然製程與操作簡單，但在短距離內驅動力不足，導致液珠遷移能力薄弱。因此藉由結合其他驅動方法或是改變接觸面的性質等方式，提高熱毛細驅動液珠的遷移能力。
在能夠利用表面物理性改質提高液珠遷移效果的基礎上，本文以乾蝕刻在矽表面製作不同間距的柱狀微結構陣列。另在微結構區域周圍建立側壁，利用側壁將液珠兩側侷限，亦使液珠呈現形狀規則的膠囊狀，降低力學分析上因液珠形狀劇烈改變帶來的影響。並以液膜包覆的形式對結構間隙進行預濕潤處理，避免液珠在遷移過程中因結構間隙而損失體積。
待試片兩端高溫區與低溫區的溫度穩定後，藉由比較不同結構間距試片上液珠的遷移狀況，發現有臨界間距存在。小於臨界間距時降低溫度梯度會讓遷移能力上升，大於臨界間距則反之。並進一步對液珠進行力學分析，發現液珠主要受到恆為負向的黏滯阻力、恆為正向的馬蘭哥尼驅動力、時正時負的內部毛細回流所影響。此外，在結構間隙內部還有一作用力，會將間隙內部的流體由高溫處液體往低溫處傳輸，但其傳輸效果會受到液珠遷移速度抑制。隨著加大結構間距，液珠不管是形狀或內部溫度分布都會更加扭曲，導致誤差與其他未考量分力的影響變大。
從固定結構間距的觀點上，熱毛細力與溫度梯度大小有正相關性。但液珠遷移過程中隨時間展延的跨距，對熱毛細力的影響卻不大。從固定溫度梯度的觀點上，加大結構間距會使低溫度梯度條件之液珠遷移效果下降，高溫度梯度條件之液珠遷移效果上升。在大於臨界間距，遷移能力受到前沿後沿接觸角的影響會大於液珠跨距的影響。
;Thermocapillary phenomenon is caused by the temperature difference inside the liquid, which makes the surface tension gradient, and then generates traction in a specific direction. In previous researches, process and operation of driving droplet with thermocapillary method is simple and cost lower, but insufficient driving force in short distance causes droplet migrate slowly. Therefore, improves droplet migration speed by changing surface properties or combining other driving methods.
In the design, based on surface physical modification can improve the droplet migration, using dry-etching to fabricate columnar microstructure arrays with different pitches on the silicon wafer. Establish a side wall around the microstructure area confining the droplet and make it appear in a regular capsule shape, be expected to reduce the effects of changes in the shape of the droplet in migration. In the operation, utilizing prewetting the structural gaps by liquid film to avoid volume loss during droplet migration on gaps.
After the temperature in hot and cold zones of test piece is stable, it is found that a critical structural gap distance exists by comparing the migration of droplet on test pieces with different structure intervals. Decreasing the temperature gradient when the gap distance is smaller than the critical distance will increase the migration ability, and vice versa when it is larger than the critical distance. From the mechanical analysis of droplet, found that the droplet is mainly affected by negative viscous resistance, positive Marangoni driving force, and unstable internal capillary reflow. In addition, there is a force inside the structural gap which will transfer the fluid inside the gap from high temperature zone to low temperature zone, but the transmission capacity will be suppressed by droplet migration speed. As the structure gap distance is increased, both the shape of droplet and the internal temperature distribution will become more distorted, resulting in greater influence of calculation errors and unconsidered forces.
From the viewpoint of fixed structure spacing, the thermal capillary force has a positive correlation with the temperature gradient. And the continuous extension of the droplet span during the migration process has just little effect on the thermal capillary force. From the viewpoint of fixed temperature gradient, increasing the structure gap distance will reduce the droplet migration effect under low temperature gradient conditions, and increase the droplet migration effect under high temperature gradient conditions. When the gap distance above the critical value, the migration capacity if affected by the contact angle more than the droplet span. |
