Institute for Botany, Faculty of Biology, Technische Universität Dresden, 01062, Dresden, Germany.
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
Sci Rep. 2020 Nov 4;10(1):16925. doi: 10.1038/s41598-020-74029-5.
Buds of horse-chestnut trees are covered with a viscous fluid, which remains sticky after long-term exposure to heat, frost, radiation, precipitation, deposition of aerosols and particles, attacks by microbes and arthropods. The present study demonstrates that the secretion does not dry out under arid conditions, not melt at 50 °C, and not change significantly under UV radiation or frost at a microscopic level. It is slightly swellable under wet conditions; and, it universally wets and adheres to substrates having different polarities. Measured pull-off forces do not differ between hydrophilic and lipophilic surfaces, ranging between 58 and 186 mN, and resulting in an adhesive strength up to 204 kPa. The mechanical and chemical properties of secretion resemble those of pressure-sensitive adhesives. The Raman, infrared, and nuclear magnetic resonance spectra show the clear presence of saturated aliphatic hydrocarbons, esters, free carboxylic acids, as well as minor amounts of amides and aromatic compounds. We suggest a multi-component material (aliphatic hydrocarbon resin), including alkanes, fatty acids, amides, and tackifying terpenoids embedded in a fluid matrix (fatty acids) comprising nonpolar and polar portions serving the universal and robust adhesive properties. These characteristics matter for ecological-evolutionary aspects and can inspire innovative designs of multifunctional, biomimetic pressure-sensitive adhesives and varnishes.
七叶树树芽被粘性分泌物所覆盖，这种分泌物在长期暴露于热、霜、辐射、降水、气溶胶和颗粒沉积、微生物和节肢动物的攻击下仍然具有粘性。本研究表明，分泌物在干旱条件下不会变干，在 50°C 下不会融化，在微观水平上也不会因紫外线辐射或霜而发生显著变化。在潮湿条件下，它具有轻微的溶胀性；并且，它普遍润湿并附着于具有不同极性的基底。测量的剥离力在亲水和疏水面之间没有差异，范围在 58 到 186 mN 之间，导致粘合强度高达 204 kPa。分泌物的机械和化学性质类似于压敏胶。拉曼、红外和核磁共振谱清楚地显示出饱和脂肪族碳氢化合物、酯、游离羧酸，以及少量酰胺和芳香族化合物的存在。我们提出了一种多组分材料（脂肪族碳氢化合物树脂），包括嵌入在包含非极性和极性部分的流体基质（脂肪酸）中的烷烃、脂肪酸、酰胺和增粘萜烯，这些部分赋予了普遍且强大的粘合性能。这些特性对生态进化方面很重要，并为多功能仿生压敏胶和清漆的创新设计提供了灵感。
