Department of Mechanical Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.
International Institute for Carbon Neutral Energy Research (WPI-I2CNER) , Kyushu University , 744 Moto-oka , Nishi-ku, Fukuoka 819-0395 , Japan.
ACS Nano. 2019 Nov 26;13(11):13343-13353. doi: 10.1021/acsnano.9b06687. Epub 2019 Oct 16.
Solid-liquid interactions are ubiquitous phenomena in nature and industry. Wettability of a liquid on a solid is governed by the chemical heterogeneity and physical roughness of the solid surface and can be characterized by measuring the advancing and receding contact angles of the liquid droplet residing on the solid. To characterize contact angle, goniometry and the Wilhelmy plate method have been widely used. Although powerful, these methods have difficulty characterizing microdroplets, can be cumbersome and expensive, and have trouble handling surfaces with local wetting heterogeneity and deformed noncircular contact lines. Furthermore, past methods are incapable of measuring contact angle during experiments (, condensation). Here, we develop simple yet powerful contact angle measurement techniques using conventional optical microscopy that utilizes focal plane shift imaging, ray optics, and wave interference. We used our techniques to study the wetting characteristics for a wide range of water droplet diameters (10 μm < < 600 μm) and apparent contact angles (0° ≤ θ ≤ 180°). The outcomes of this work establish a powerful tool to more easily and rapidly characterize microscale droplet advancing and receding contact angles.
固液相互作用是自然界和工业中普遍存在的现象。液体在固体上的润湿性由固体表面的化学不均匀性和物理粗糙度决定，可以通过测量液体在固体上驻留的液滴的前进和后退接触角来表征。为了表征接触角，已广泛使用测角法和吊片法。尽管这些方法功能强大，但它们在表征微液滴方面存在困难，可能繁琐且昂贵，并且难以处理具有局部润湿性不均匀和变形非圆形接触线的表面。此外，过去的方法无法在实验过程中测量接触角（例如，冷凝）。在这里，我们使用常规光学显微镜开发了简单而强大的接触角测量技术，该技术利用焦面移位成像、光线光学和波干涉。我们使用这些技术研究了大范围的水滴直径（10μm < < 600μm）和表观接触角（0°≤θ≤180°）的润湿特性。这项工作的结果为更轻松、更快速地表征微尺度液滴前进和后退接触角提供了有力的工具。
