Mechanics of Insect Adhesion

许多昆虫分泌液体以粘附在表面上，使它们即使在光滑的表面上也能垂直和倒置地爬行。然而，如何实现这一目标的细节仍不清楚。关于粘合剂的性质以及粘合剂的操作动力学存在公开的问题。该项目将侧重于开发不同拟议机制的模型，这些模型可以与生物学文献中的现有数据以及Walter Federle实验室（动物学，剑桥）的新实验进行比较。从生物学的角度来看，了解这种粘合剂的作用是很重要的，也是在人造粘合剂中利用类似机制的第一步。第一条链的动机是观察到许多昆虫使用的液体分泌物是水滴在油中的乳液。然而，这种乳液的目的尚不清楚：昆虫是否依赖于许多毛细管桥的形成，然后提供大的粘附力，或者乳液是一种改变粘合剂动态特性的方法（例如，通过给予它有限的屈服应力）？我将开发这种乳液的模型，重点是了解力位移响应，如果毛细管桥是重要的。我也将开始了解这种乳液是如何老化的，例如通过奥斯特瓦尔德熟化。第二条线涉及流体通过昆虫的粘附器的囊分泌的方式。在此之前，这一直是使用简单的盒子模型，忽略了一些重要的力学问题。我将开发基于物理的模型，以更好地理解这种分泌过程以及当昆虫希望从表面脱离时，它是如何逆转的：以前的实验观察表明，根据昆虫如何从表面脱离，分泌物要么留在表面上，要么被移除（可能被重新吸收到昆虫的粘附器官中）。这是一个关于昆虫粘附中的被动机制的例子，我们还完全没有弄清楚，我将采用的方法将涉及建立一个数学模型的层次结构，以了解这种粘合剂是如何工作的。在这里，我将受益于小组现有的专业知识，有关表面张力主导的现象，特别是因为它适用于软物体的变形。我还将确保与Walter Federle小组和Robert Style（材料科学，ETH-苏黎世）的实验人员密切合作：这将使我能够开发生物相关的模型（Federle小组），同时也能够在理想化的场景中进行定量测试（Rob Style）。这种数学技术（渐近分析和一些数值技术）的结合，对来自生物和理想系统的真实的实验数据进行了测试，使得这项研究既及时又新颖。

Many insects secrete liquids in order to adhere to surfaces, allowing them to climb vertically and upside-down even on smooth surfaces. However, the details of how this is achieved remain unclear. There are open questions about the nature of the adhesive, as well as the dynamics of operation of the adhesive. This project will focus on developing models of different proposed mechanisms that can be compared with existing data in the biological literature, as well as new experiments from the laboratory of Walter Federle (Zoology, Cambridge). An understanding of the operation of such adhesives is important both from a biological perspective, and also as a first step in exploiting similar mechanisms in man-made adhesives.There are two key strands of the project. The first strand is motivated by the observation that the liquid secretion used by many insects is an emulsion of water droplets in oil. However, the purpose of this emulsion is unclear: does the insect rely on the formation of many capillary bridges that then provide a large adhesive force or is the emulsion instead a way to modify the dynamic properties of the adhesive (for example by giving it a finite yield stress)? I will develop models of such emulsions focussed on understanding the force-displacement response that would be expected if capillary bridges were important. I will also begin to understand how such emulsions age, for example through Ostwald ripening.The second strand concerns the manner in which the fluid is secreted through the sac of the insect's adhesive apparatus. Previously, this has been modelled using simple box-models that neglect some of the important mechanics of the problem. I will develop physically-based models to better understand both this secretion process and how it may be reversed when the insect wishes to detach from a surface: previous experimental observations have suggested that depending on how the insect detaches from the surface, the secretion is either left behind on the surface or removed (presumably being reabsorbed into the insect's adhesive apparatus). This is one example of suspected passive mechanisms in insect adhesion that are not at all understood.The approach that I will adopt will involve the development of a hierarchy of mathematical models to understand how such adhesives operate. Here I will benefit from the existing expertise in the group concerning surface tension-dominated phenomena, particularly as it applies to the deformation of soft objects. I will also ensure that I work closely with experimentalists both in Walter Federle's group and with Robert Style (Materials Science, ETH-Zurich): this will allow me to develop models that are biologically relevant (Federle group), whilst also being able to perform quantitative tests in idealised scenarios (Rob Style). This combination of mathematical techniques (asymptotic analysis and some numerical techniques) tested against real experimental data from biological and idealised systems makes this research both timely and novel.This project falls within the EPSRC Fluid Dynamics research area