Department of Mechanical and Nuclear Engineering , Virginia Commonwealth University , Richmond , Virginia 23284-3015 , United States.
The Nonwovens Institute , NC State University , Raleigh , North Carolina 27695-7103 , United States.
Langmuir. 2018 Oct 16;34(41):12488-12499. doi: 10.1021/acs.langmuir.8b02810. Epub 2018 Oct 1.
Water droplet mobility on a hydrophobic surface cannot be guaranteed even when the droplet exhibits a high contact angle (CA) with the surface. In fact, droplet mobility on a surface, especially a fibrous surface, has remained an unsolved empirical problem. This paper is a combined experimental-computational study focused on droplet mobility on a fibrous surface. Electrospun polystyrene (PS) coatings were used in this work for their ability to exhibit high CAs simultaneously with low droplet mobility. To simplify this otherwise complicated problem and better isolate droplet-fiber interactions, the orientation of the fibers in the coatings was limited to the x and y directions. As the earth gravity was not strong enough to mobilize small droplets on PS coatings, experiments were conducted using ferrofluid droplets, and a magnet was used to make them move on the surface. Experimentally validated numerical simulations were used to enhance our understanding of the forces acting on a droplet before moving on the surface. Effects of Young-Laplace CA and fiber-fiber spacing on droplet mobility were investigated. In particular, it was found that droplet mobility depends strongly on the balance of forces exerted on the droplet by the fibers on the receding and advancing sides.
即使液滴与表面呈现出高接触角（CA），也不能保证液滴在疏水性表面上的移动性。事实上，液滴在表面上的移动性，特别是在纤维表面上的移动性，一直是一个未解决的经验问题。本文是一项结合实验和计算的研究，重点研究液滴在纤维表面上的移动性。在这项工作中，使用了静电纺丝聚苯乙烯（PS）涂层，因为它们能够同时表现出高 CA 和低液滴移动性。为了简化这个复杂的问题，并更好地隔离液滴-纤维相互作用，涂层中纤维的方向被限制在 x 和 y 方向。由于地球引力不足以使 PS 涂层上的小液滴移动，因此使用铁磁液滴进行了实验，并使用磁铁使它们在表面上移动。使用经过实验验证的数值模拟来增强我们对表面移动前作用在液滴上的力的理解。研究了杨氏接触角和纤维-纤维间距对液滴移动性的影响。特别是，发现液滴的移动性强烈取决于在后退和前进侧上纤维对液滴施加的力的平衡。
