Mockenhaupt Bernd, Ensikat Hans-Jürgen, Spaeth Manuel, Barthlott Wilhelm
Nees Institute for Biodiversity of Plants, University of Bonn, Meckenheimer Allee 170, D-53115 Bonn, Germany.
Langmuir. 2008 Dec 2;24(23):13591-7. doi: 10.1021/la802351h.
The stability of superhydrophobic properties of eight plants and four technical surfaces in respect to water condensation has been compared. Contact and sliding angles were measured after application of water drops of ambient temperature (20 degrees C) onto cooled surfaces. Water evaporating from the drops condensed, due to the temperature difference between the drops and the surface, on the cooled samples, forming "satellite droplets" in the vicinity of the drops. Surface cooling to 15, 10, and 5 degrees C showed a gradual decrease of superhydrophobicity. The decrease was dependent on the specific surface architecture of the sample. The least decrease was found on hierarchically structured surfaces with a combination of a coarse microstructure and submicrometer-sized structures, similar to that of the Lotus leaf. Control experiments with glycerol droplets, which show no evaporation, and thus no condensation, were carried out to verify that the effects with water were caused by condensation from the drop (secondary condensation). Furthermore, the superhydrophobic properties after condensation on cooled surfaces from a humid environment for 10 min were examined. After this period, the surfaces were covered with spherical water droplets, but most samples retained their superhydrophobicity. Again, the best stability of the water-repellent properties was found on hierarchically structured surfaces similar to that of the Lotus leaf.
比较了八种植物表面和四种工业表面超疏水性能在水凝结方面的稳定性。将室温（20摄氏度）的水滴施加到冷却表面后，测量接触角和滑动角。由于水滴与表面之间的温差，从水滴蒸发的水在冷却的样品上凝结，在水滴附近形成“卫星液滴”。将表面冷却至15、10和5摄氏度时，超疏水性逐渐降低。这种降低取决于样品的特定表面结构。在具有粗微观结构和亚微米级结构组合的分级结构表面上发现的降低最小，类似于荷叶的结构。进行了甘油滴的对照实验，甘油滴不蒸发，因此不凝结，以验证水的影响是由液滴的凝结（二次凝结）引起的。此外，还研究了在潮湿环境中冷却表面上凝结10分钟后的超疏水性能。在此期间后，表面覆盖着球形水滴，但大多数样品仍保持其超疏水性。同样，在类似于荷叶的分级结构表面上发现了拒水性能的最佳稳定性。
