Chair of Functional Materials, Department of Material Science and Engineering, Campus D3 3, 66123 Saarbrücken, Germany.
J Colloid Interface Sci. 2022 Mar;609:645-656. doi: 10.1016/j.jcis.2021.11.071. Epub 2021 Nov 17.
Wetting characterization and the production of engineered surfaces showing distinct contact angles or spreading behavior is of major importance for many industrial and scientific applications. As chemical composition plays a major role in the wetting behavior of flat samples, wettability, capillary forces and resulting droplet spreading on anisotropic surface patterns are expected to be highly dependent on surface chemistry as well.
To gain understanding of the fundamental principles of the interplay between surface topography and surface chemistry regarding water wettability, anisotropic line patterns were produced on steel samples in a direct laser writing process. Homogeneous surface coatings allowed for a chemical masking of the laser patterns and therewith the identification of the influence of surface chemistry on static contact angles and wetting anisotropy.
While a carbon coating leads to pronounced wettability and spreading along the topographic anisotropy, an inert gold-palladium coating can fully suppress anisotropic droplet spreading. Model calculations show that an amorphous carbon coating leads to Wenzel wetting while the gold-palladium coating causes air inclusions between the water and the surface in the Cassie-Baxter wetting state. Only in combination with the right chemical composition of the surface, directional patterns show their potential of anisotropic wetting behavior.
润湿特性的表征以及具有不同接触角或铺展行为的工程表面的制造在许多工业和科学应用中都具有重要意义。由于化学成分在平板样品的润湿行为中起着主要作用,因此预计各向异性表面图案的润湿性、毛细作用力和由此产生的液滴铺展也高度依赖于表面化学。
为了深入了解表面形貌和表面化学之间在水润湿性方面相互作用的基本原理,在钢样品上通过直接激光写入工艺生成各向异性的线图案。均匀的表面涂层可以对激光图案进行化学掩蔽,从而确定表面化学对静态接触角和润湿性各向异性的影响。
虽然碳涂层会导致明显的润湿性和沿地形各向异性的铺展,但惰性的金钯涂层可以完全抑制各向异性的液滴铺展。模型计算表明,无定形碳涂层会导致 Wenzel 润湿,而金钯涂层会导致水和表面之间存在空气夹杂物,处于 Cassie-Baxter 润湿状态。只有与表面的正确化学成分相结合,定向图案才能显示其各向异性润湿行为的潜力。