School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287-1604, United States.
School for Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287-1604, United States.
Langmuir. 2016 May 10;32(18):4681-7. doi: 10.1021/acs.langmuir.6b00762. Epub 2016 Apr 22.
Insects of the order Embioptera, known as embiopterans, embiids, or webspinners, weave silk fibers together into sheets to make shelters called galleries. In this study, we show that silk galleries produced by the embiopteran Antipaluria urichi exhibit a highly hydrophobic wetting state with high water adhesion macroscopically equivalent to the rose petal effect. Specifically, the silk sheets have advancing contact angles above 150°, but receding contact angle approaching 0°. The silk sheets consist of layered fiber bundles with single strands spaced by microscale gaps. Scanning and transmission electron microscopy (SEM, TEM) images of silk treated with organic solvent and gas chromatography mass spectrometry (GC-MS) of the organic extract support the presence of a lipid outer layer on the silk fibers. We use cryogenic SEM to demonstrate that water drops reside on only the first layer of the silk fibers. The area fraction of this sparse outer silk layers is 0.1 to 0.3, which according to the Cassie-Baxter equation yields an effective static contact angle of ∼130° even for a mildly hydrophobic lipid coating. Using high magnification optical imaging of the three phase contact line of a water droplet receding from the silk sheet, we show that the high adhesion of the drop stems from water pinning along bundles of multiple silk fibers. The bundles likely form when the drop contact line is pinned on individual fibers and pulls them together as it recedes. The dynamic reorganization of the silk sheets during the droplet movement leads to formation of "super-pinning sites" that give embiopteran silk one of the strongest adhesions to water of any natural hydrophobic surface.
缨翅目昆虫，又称缨翅目昆虫、缨翅目昆虫或织网者，将丝纤维编织在一起形成称为通道的遮蔽物。在这项研究中，我们表明，由缨翅目昆虫 Antipaluria urichi 产生的丝通道表现出高度疏水的润湿状态，具有宏观上与玫瑰花瓣效应相当的高水附着力。具体来说，丝片的前进接触角大于 150°，但后退接触角接近 0°。丝片由分层纤维束组成，单丝之间有微尺度间隙。用有机溶剂处理的丝的扫描和透射电子显微镜（SEM、TEM）图像以及有机提取物的气相色谱-质谱（GC-MS）支持丝纤维上存在脂质外层。我们使用低温 SEM 证明水滴仅位于丝纤维的第一层上。这种稀疏的外丝层的面积分数为 0.1 到 0.3，根据 Cassie-Baxter 方程，即使对于轻度疏水性的脂质涂层，也会产生约 130°的有效静态接触角。通过对从丝片上退去的水滴的三相接触线进行高倍光学成像，我们表明，水滴的高附着力源于沿着多根丝纤维束的水钉扎。当液滴接触线被固定在单个纤维上并随着其退去而将它们拉在一起时，可能会形成纤维束。在液滴运动过程中丝片的动态重组导致形成“超级钉扎点”，使缨翅目昆虫的丝对水的附着力成为任何天然疏水性表面中最强的之一。
