Mayser Matthias J, Barthlott Wilhelm
*Microfluidics, Department of Aerospace and Mechanical Engineering, University of Liege, Chemin des Chevreuils 1, 4000 Liege, Belgium; Nees Institute for Biodiversity of Plants, University of Bonn, Venusbergweg 22, 53115 Bonn, Germany *Microfluidics, Department of Aerospace and Mechanical Engineering, University of Liege, Chemin des Chevreuils 1, 4000 Liege, Belgium; Nees Institute for Biodiversity of Plants, University of Bonn, Venusbergweg 22, 53115 Bonn, Germany *Microfluidics, Department of Aerospace and Mechanical Engineering, University of Liege, Chemin des Chevreuils 1, 4000 Liege, Belgium; Nees Institute for Biodiversity of Plants, University of Bonn, Venusbergweg 22, 53115 Bonn, Germany
*Microfluidics, Department of Aerospace and Mechanical Engineering, University of Liege, Chemin des Chevreuils 1, 4000 Liege, Belgium; Nees Institute for Biodiversity of Plants, University of Bonn, Venusbergweg 22, 53115 Bonn, Germany.
Integr Comp Biol. 2014 Dec;54(6):1001-7. doi: 10.1093/icb/icu072. Epub 2014 Jun 12.
Superhydrophobic, hierarchically structured, technical surfaces (Lotus-effect) are of high scientific and economic interest because of their remarkable properties. Recently, the immense potential of air-retaining superhydrophobic surfaces, for example, for low-friction transport of fluids and drag-reducing coatings of ships has begun to be explored. A major problem of superhydrophobic surfaces mimicking the Lotus-effect is the limited persistence of the air retained, especially under rough conditions of flow. However, there are a variety of floating or diving plant and animal species that possess air-retaining surfaces optimized for durable water-repellency (Salvinia-effect). Especially floating ferns of the genus Salvinia have evolved superhydrophobic surfaces capable of maintaining layers of air for months. Apart from maintaining stability under water, the layer of air has to withstand the stresses of water pressure (up to 2.5 bars). Both of these aspects have an application to create permanent air layers on ships' hulls. We investigated the effect of pressure on air layers in a pressure cell and exposed the air layer to pressures of up to 6 bars. We investigated the suppression of the air layer at increasing pressures as well as its restoration during decreases in pressure. Three of the four examined Salvinia species are capable of maintaining air layers at pressures relevant to the conditions applying to ships' hulls. High volumes of air per surface area are advantageous for retaining at least a partial Cassie-Baxter-state under pressure, which also helps in restoring the air layer after depressurization. Closed-loop structures such as the baskets at the top of the "egg-beater hairs" (see main text) also help return the air layer to its original level at the tip of the hairs by trapping air bubbles.
超疏水、具有层次结构的技术表面（荷叶效应）因其卓越性能而具有很高的科学和经济价值。最近，例如用于流体低摩擦输送和船舶减阻涂层的空气留存超疏水表面的巨大潜力已开始得到探索。模仿荷叶效应的超疏水表面的一个主要问题是所留存空气的持久性有限，尤其是在粗糙的流动条件下。然而，有多种漂浮或潜水的动植物物种拥有为持久防水性（槐叶萍效应）而优化的空气留存表面。特别是槐叶萍属的漂浮蕨类植物已经进化出能够保持空气层数月的超疏水表面。除了在水下保持稳定性外，空气层还必须承受水压（高达2.5巴）的压力。这两个方面都可应用于在船舶船体上创建永久空气层。我们在压力室中研究了压力对空气层的影响，并使空气层承受高达6巴的压力。我们研究了压力增加时空气层的抑制情况以及压力降低时空气层的恢复情况。在所研究的四种槐叶萍物种中，有三种能够在与船舶船体适用条件相关的压力下保持空气层。每单位表面积的大量空气有利于在压力下至少保持部分卡西 - 巴克斯特状态，这也有助于在减压后恢复空气层。诸如“打蛋器毛”顶部的篮状结构（见正文）等闭环结构也有助于通过捕获气泡使空气层在毛的尖端恢复到原始水平。
