液滴在孔洞結構表面上的濕潤行為之研究

Abstract

濕潤行為的觀察在許多工業領域中扮演重要的角色，具有相當多的應用。在本篇研究中，我們將利用實驗及模擬兩種方法來觀測粗糙疏水表面的濕潤行為。在實驗中，我們研究方孔陣列微結構疏水表面，透過改變方孔尺寸、方孔間距及方孔深度來觀察其濕潤性的變化。觀察液滴在表面上濕潤行為的方式包括前進、後退角及滑動角的量測。我們所用的方孔深度變化範圍從0.5μm到15μm，能夠觀察到液滴在Wenzel及Cassie的濕潤狀態。在實驗中，我們還利用雙版擠壓對液滴施加壓力，觀察濕潤現象轉換的可能性。在模擬部分，我們利用Surface Evolver 模擬液滴在疏水餘弦陣列表面上的濕潤行為。觀察其前進、後退角及Cassie-Wenzel濕潤現象轉換的行為。固定體積的液體在不同粗糙度的表面上，會有許多不同的亞穩態。液滴在每個不同的亞穩態都具有其對應的接觸角，在某表面上其最大及最小的角度分別是其前進角及後退角。透過增加表面的粗糙度，我們能夠觀察液滴從Wenzel狀態變成Cassie狀態的濕潤現象轉換。在本篇研究，我們會比較實驗及模擬得到的結果，並進行討論，探討透過兩種不同分析方式所得到的共同處。此外，我們還將本篇研究和液滴在方柱陣列微結構疏水表面上的濕潤行為做比較，觀察兩者的差異性及共通性。

In this study, we observe the wetting behavior of the hydrophobic rough surfaces in two different ways including experiments and simulation. Wetting behavior plays an important role in various industry and has a number of applications. In experiments, we investigate the wetting behavior of hydrophobic, microstructured surfaces containing square array of holes, and observe their wettability by vary the width of hole, spacing and the depth of hole. We measure the advancing contact angles, the receding contact angles and the sliding angles to determine the wetting behavior of the water droplet on the surface. Due to the wide range of the depth (from 0.5 μm to 15 μm), both the Wenzel state and the Cassie state can be observed. We use the squeeze test to check whether the wetting transition between two different wetting states will occur. In the simulation, we simulate a water droplet sitting on a hydrophobic surface with a cosine wave-like square array pattern to determine the contact angle and study on the Cassie-Wenzel wetting transition by the Surface Evolver. At different surface roughnesses, we can obtain multiple metastable states for a fixed droplet volume. Each metastable state represents a contact angle of the liquid droplet. The maximum and minimum contact angles correspond to the advancing/ receding contact angles. By increasing the surface roughness, the wetting transition from the Wenzel state to the Cassie state will be induced. The results from the experiments and the simulation will be discussed and compared. We find there are some common results from two different ways of analysis of wetting behavior on hydrophobic surfaces with hole array pattern. Besides, we also compare the results from this study to the wetting behavior of hydrophobic, microstructured surfaces containing square array of pillars done by previous researches. Seeing the difference and the common parts between two different structures.