Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave. 3-461B, Cambridge, Massachusetts 02139, USA.
Nat Mater. 2010 May;9(5):413-7. doi: 10.1038/nmat2726. Epub 2010 Mar 28.
Controlling surface wettability and liquid spreading on patterned surfaces is of significant interest for a broad range of applications, including DNA microarrays, digital lab-on-a-chip, anti-fogging and fog-harvesting, inkjet printing and thin-film lubrication. Advancements in surface engineering, with the fabrication of various micro/nanoscale topographic features, and selective chemical patterning on surfaces, have enhanced surface wettability and enabled control of the liquid film thickness and final wetted shape. In addition, groove geometries and patterned surface chemistries have produced anisotropic wetting, where contact-angle variations in different directions resulted in elongated droplet shapes. In all of these studies, however, the wetting behaviour preserves left-right symmetry. Here, we demonstrate that we can harness the design of asymmetric nanostructured surfaces to achieve uni-directional liquid spreading, where the liquid propagates in a single preferred direction and pins in all others. Through experiments and modelling, we determined that the spreading characteristic is dependent on the degree of nanostructure asymmetry, the height-to-spacing ratio of the nanostructures and the intrinsic contact angle. The theory, based on an energy argument, provides excellent agreement with experimental data. The insights gained from this work offer new opportunities to tailor advanced nanostructures to achieve active control of complex flow patterns and wetting on demand.
控制具有图案表面的润湿性和液体铺展对于广泛的应用具有重要意义，包括 DNA 微阵列、数字化芯片实验室、防雾和集雾、喷墨打印和薄膜润滑。通过表面工程的进步，制造各种微/纳米尺度的形貌特征和表面的选择性化学图案化，提高了表面润湿性，并能够控制液膜厚度和最终润湿形状。此外，沟槽几何形状和图案化表面化学性质产生了各向异性润湿，其中不同方向的接触角变化导致液滴形状拉长。然而，在所有这些研究中，润湿行为保持了左右对称。在这里，我们证明我们可以利用不对称纳米结构表面的设计来实现单向液体铺展，其中液体在一个单一的首选方向上传播，并在所有其他方向上固定。通过实验和建模，我们确定了扩展特性取决于纳米结构的不对称程度、纳米结构的高度与间距比以及固有接触角。该理论基于能量论证，与实验数据非常吻合。这项工作的见解为定制先进的纳米结构以实现对复杂流动模式和按需润湿的主动控制提供了新的机会。
