School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Korea.
Langmuir. 2010 Jun 1;26(11):8319-26. doi: 10.1021/la9047402.
Most naturally existing superhydrophobic surfaces have a dual roughness structure where the entire microtextured area is covered with nanoscale roughness. Despite numerous studies aiming to mimic the biological surfaces, there is a lack of understanding of the role of the nanostructure covering the entire surface. Here we measure and compare the nonwetting behavior of microscopically rough surfaces by changing the coverage of nanoroughness imposed on them. We test the surfaces covered with micropillars, with nanopillars, with partially dual roughness (where micropillar tops are decorated with nanopillars), and with entirely dual roughness and a real lotus leaf surface. It is found that the superhydrophobic robustness of the surface with entirely dual roughness, with respect to the increased liquid pressure caused by the drop evaporation and with respect to the sagging of the liquid meniscus due to increased micropillar spacing, is greatly enhanced compared to that of other surfaces. This is attributed to the nanoroughness on the pillar bases that keeps the bottom surface highly water-repellent. In particular, when a drop sits on the entirely dual surface with a very low micropillar density, the dramatic loss of hydrophobicity is prevented because a novel wetting state is achieved where the drop wets the micropillars while supported by the tips of the basal nanopillars.
大多数自然存在的超疏水表面具有双重粗糙度结构，整个微纹理区域都覆盖着纳米级粗糙度。尽管有许多旨在模拟生物表面的研究，但对于覆盖整个表面的纳米结构的作用仍缺乏了解。在这里，我们通过改变施加在表面上的纳米粗糙度的覆盖率来测量和比较微观粗糙表面的不润湿行为。我们测试了覆盖有微柱、纳米柱、部分双重粗糙度（微柱顶部装饰有纳米柱）和完全双重粗糙度以及真实荷叶表面的表面。结果发现，与其他表面相比，具有完全双重粗糙度的表面在由于液滴蒸发引起的液体压力增加以及由于微柱间距增加导致的液体弯月面下垂方面的超疏水性鲁棒性得到了极大的增强。这归因于柱基上的纳米粗糙度，它使底面保持高度疏水。特别是，当液滴坐在具有非常低的微柱密度的完全双重表面上时，由于达到了一种新的润湿状态，即液滴在基底纳米柱的尖端支撑下润湿微柱，从而防止了疏水性的急剧丧失。
