固液界面性質與表面熱滲流成因之研究

Abstract

熱滲流為溫度梯度而產生的流動，此流動在多孔物質材料中已被研究探討多年，迄今仍沒有完整且通用的模型與機制。同樣因溫度梯度產生物質流現象的膠體粒子熱泳研究中指出，將膠體粒子固定於一溫度梯度中，該粒子的周圍會產生一流動稱為滑移流，其方向與該粒子本身熱泳方向相反，但此文獻中並未對滑移流作直接的量測。本實驗希望利用在平板表面製造一溫度梯度，進而了解溫度梯度所造成的流動與多孔物質材料中的熱滲流、膠體粒子表面之滑移流間的關聯性及成因。本實驗著重於表面性質對於該流動所產生的影響，研究方法為對基材表面作氧電漿表面改質及改變其表面電荷密度，觀察不同表面特性所對應的流動情形，並且利用二氧化矽粒子來追蹤因基材表面溫度梯度而產生流場現象。在本實驗的主要結果中，當基材表面巨觀的接觸角不同時，其因溫度梯度而產生的表面流動現象也會有所不同，並且隨著表面親水程度越強(接觸角越小)，其流動速度會逐漸變小，甚至發生流動方向相反(原流動方向為低溫至高溫)的情形。熱滲流相關文獻中提及，不同多孔薄膜其形成的熱滲流方向相反，在疏水薄膜上其流動由低溫流向高溫；膠體粒子熱泳中，聚苯乙烯粒子表面疏水，其熱泳方向由高溫處往低溫移動，若其表面確實有所謂滑移流，則該流動方向由低溫流向高溫，這些結果皆與本實驗相符，因此溫度梯度而產生的物質流動，確實與表面性質有極大的相關。

Thermophoresis is a phenomenon when there exists a temperature gradient, and it would cause a matter flow. Previous research on thermophoresis suggests that it is caused by the slip flow which has been observed around particles. When a particle is fixed in an area with a temperature gradient, the flow happens in the opposite direction against thermophoresis. However, the research does not go any further and does not suggest how and why slip flow is generated. We are interested in if these two phenomena caused by the temperature gradient alike are related. If a particle is huge enough, a tiny part of the surface can be treated as a plane. Thus, the problem can be simplified and we need to consider what happens in the solid-liquid interface. In addition, slip flow is equivalent to thermos-osmosis which is defined as the flow generated by temperature gradient in the interface. The results shows that the wettability has a significant effect on the flow: here in after, the contact angle is used as the index of wettability. When θ = 30∘, driving forces equilibrated and no flow occurred. When θ > 30∘, the flow from the cold side to the hot side occurred. Reversely when θ < 30∘, the flow from the hot side to the cold side occurred. This result accords with the research of thermos-osmosis in porous materials. In addition, changing the property of particle surface shows that the direction of thermophoresis is related to its surface property. Hydrophobic PS (polystyrene) particle escapes from hot side in usual. Neither thermophoresis nor thermos-osmosis have been understand fully and almost do experiment indirectly. In our research, thermos-osmosis would not only follow the prediction but also thermophoresis. This suggest will make the research on the mechanism of thermophoresis simpler.