本實驗藉由水滴潤濕物質表面，加上外界氣相三相所造成三方向的張力來維持系統平衡，利用楊氏方程式(Young’s equation)熱力學平衡，而在液滴與物質接觸處出現一個角度，定義為接觸角(contact angle)，接觸角是一個界定濕潤程度(wettability)的指標，也能判別物質的親疏水性。 生活中常接觸不同的溶劑，其中存在少數相似界面活性劑的特性，例如濕潤效果極佳、會產生微胞(micelle)等特性。業界常用的去光阻劑BDG就是這類溶劑，因此可利用接觸角界定其潤濕程度，利用密度計、聲速計等儀器來分析其是否產生微胞的證據，甚至再文獻中得知可利用核磁共振儀(NMR)來判斷形成微胞時的分子數，以區分BDG與傳統界面活性劑的相關性。 從上述的楊氏熱力學平衡，固定液體種類與固體材料，加上氣相是不會變的空氣，可知液體與固體所形成的接觸角理當固定(排除小誤差)，但實驗過程中發現在某些條件下(此實驗指亦體接觸邊界)，系統仍會維持平衡，但卻違反Young’s equation，所以利用熱力學平衡穩態時能量最低重新推導一套符合接處邊界時接觸角的公式，再改變不同液體與材料去分析新公式的正確性與限定條件。 We have studied the atypical nonionic surfactant 2-(2-Butoxyethoxy)-ethanol (BDG, C4E2) and unusual droplet wetting at the edge of a homogeneous surface. Owing to the short alkyl tail, BDG is typically regarded as a solvent completely miscible with water. However, our experimental results based on bulk (density and sound velocity) and surface properties (surface tension and contact angle) show that BDG possesses the typical feature of surfactant: a sudden slope change of the property-concentration curve. Nonetheless, the critical micelle concentration determined by the turning point is usually high, about 1 M. As a result, BDG possesses the dual nature of solvent and surfactant and can be a good cleaning solution for post-chemical mechanical polishing in semiconductor industry. When a droplet is deposited on a flat, homogenous surface, the intrinsic contact angle depicts the wettability of liquid on solid substrates. We perform droplet wetting experiments atop cylindrical frustums. Three different regimes are observed. In the first regime, the droplet does not reach the edge and the Young-Laplace equation is followed. After the droplet reaches the edge, the contact angle continues increasing with the liquid volume due to advanced pinning. In the second regime, the apparent contact angle cannot be described by the Young-Laplace equation. Once the droplet volume (or the contact angle) exceeds a critical value, the droplet starts to invade the slanted surface with the intrinsic contact angle or falls off like avalanche. In the third regime, the latter occurs because the gravity becomes important.
