Department of Chemical and Materials Engineering, National Central University, Jhongli, Taiwan 320, ROC.
Langmuir. 2012 Apr 3;28(13):5606-13. doi: 10.1021/la300382j. Epub 2012 Mar 20.
In this article, the contact angle hysteresis (CAH) of acrylic glass is experimentally and theoretically studied through the compression-relaxation process of droplets by using a superhydrophobic surface with negligible CAH effect. In contrast to the existing technique in which the volume of the droplet changes during the measurement of CAH, this procedure is carried out at a constant volume of the droplet. By observing the base diameter (BD) and the contact angle (CA) of the droplet during the compression-relaxation process, the wetting behavior of the droplet can be divided into two regimes, the contact line withdrawal and the contact line pinning regimes, depending on the gap thickness (H) at the end of the compression process. During the compression process, both regimes possess similar droplet behavior; the contact line will move outward and the BD will expand while the CA remains at the advancing angle. During the relaxation process, the two regimes are significantly different. In the contact line withdrawal regime, the contact line will withdraw with the CA remaining at the receding angle. In the contact line pinning regime, however, the contact line will be pinned at the final position and the CA will decline to a certain value higher than the receding angle. Furthermore, the advancing pinning behavior can also be realized through a successive compression-relaxation process. On the basis of the liquid-induced defects model, Surface Evolver simulations are performed to reproduce the behavior of the droplet during the compression-relaxation process; both contact line withdrawal and pinning regimes can also be identified. The results of the experiment and simulation agree with each other very well.
本文通过使用具有可忽略接触角滞后（CAH）效应的超疏水表面，对亚克力玻璃的接触角滞后（CAH）进行了实验和理论研究。与现有的技术不同，该技术在测量 CAH 时，液滴的体积会发生变化，而本方法则在液滴体积恒定的情况下进行。通过观察液滴在压缩-松弛过程中的基底直径（BD）和接触角（CA），可以将液滴的润湿行为分为两个区，即接触线退出区和接触线固定区，这取决于压缩过程结束时的间隙厚度（H）。在压缩过程中，两个区都具有相似的液滴行为；接触线将向外移动，BD 将扩展，而 CA 保持在前进角。在松弛过程中，两个区的行为有显著的不同。在接触线退出区，接触线将随着 CA 保持在后退角而退出。然而，在接触线固定区，接触线将被固定在最终位置，CA 将下降到一定值，高于后退角。此外，通过连续的压缩-松弛过程也可以实现前进的固定行为。基于液体诱导缺陷模型，使用 Surface Evolver 进行模拟，以再现液滴在压缩-松弛过程中的行为；可以识别出接触线退出和固定区。实验和模拟的结果非常吻合。
