Andrews Aleimah C, Duffy Sean, Edgerly Janice S, Barber Richard P
Department of Biology, Santa Clara University, Santa Clara, California 95053, USA.
Center for Nanostructures, Santa Clara University, Santa Clara, California 95053, USA.
Phys Rev E. 2022 Jul;106(1-1):014801. doi: 10.1103/PhysRevE.106.014801.
Embioptera (webspinners) are insects that construct domiciles using silk produced from their front feet. This silk is the finest known with measured single fiber diameters in the 30-140 nm range. In the wild, some webspinner silk on trees is observed to have a clothlike or shiny sheetlike appearance. Both forms of silk shield the occupants from rain water effectively: presumably valuable in tropical environments. In this article we elucidate the mechanism by which silk fibers are transformed into these structures through interaction with water. We quantify the evaporation rates of single water droplets which have been suspended on unmodified as-spun silk for two Trinidadian arboreal species: Antipaluria urichi (Clothodidae) and Pararhagadochir trinitatis (Scelembiidae). These rates are compared to those of droplets suspended on rose petals due to similar wetting properties (both hydrophobicity and pinning). We observe that on sufficiently thick silk, droplet evaporation rates decrease with time. This behavior is a result of a thin soluble film developing on the drop surface that later becomes a solid residual film. Experimentally verified theoretical models are invoked to support the results.
纺足目昆虫（结网蛛）是利用前足分泌的丝建造住所的昆虫。这种丝是已知最细的，测得的单纤维直径在30 - 140纳米范围内。在野外，观察到树上一些结网蛛的丝呈布状或有光泽的片状外观。这两种丝都能有效地保护居住者免受雨水侵袭：这在热带环境中可能很有价值。在本文中，我们阐明了丝纤维通过与水相互作用转化为这些结构的机制。我们对两种特立尼达树栖物种——乌氏反足蛛（Clothodidae科）和特立尼达拟蛛（Scelembiidae科）未改性的初纺丝上悬浮的单个水滴的蒸发速率进行了量化。由于具有相似的润湿性（疏水性和钉扎作用），将这些速率与悬浮在玫瑰花瓣上的水滴的蒸发速率进行了比较。我们观察到，在足够厚的丝上，水滴蒸发速率随时间降低。这种行为是由于液滴表面形成了一层薄的可溶膜，该膜随后变成了固体残留膜。我们引用了经过实验验证的理论模型来支持这些结果。
