Mechanics of Insect Adhesion

许多昆虫分泌液体是为了附着在表面上，即使在光滑的表面上，它们也可以垂直和颠倒地爬行。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仍存在疑问。该项目将专注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进行比较，以及来自沃尔特·费德勒(剑桥动物学)实验室的新实验。从生物学角度理解这类粘合剂的操作非常重要，也是利用人造粘合剂中类似机制的第一步。该项目有两个关键环节。第一股的动机是观察到许多昆虫使用的液体分泌物是油中水滴的乳状液。然而，这种乳剂的用途尚不清楚：昆虫是依赖于许多毛细管桥的形成，然后提供巨大的粘附力，还是乳剂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)？我将开发这种乳剂的模型，重点是了解如果毛细管桥很重要，预计会出现的力-位移响应。我还将开始了解这种乳状液是如何老化的，例如通过奥斯特瓦尔德成熟。第二股是关于液体通过昆虫粘附器的囊分泌的方式。以前，这是使用简单的盒子模型来建模的，这些模型忽略了问题的一些重要机制。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分离时，它可能如何逆转：以前的实验观察表明，根据昆虫从表面分离的方式，分泌物要么留在表面，要么被移除(假设被重新吸收到昆虫的粘合装置中)。这是昆虫粘着中疑似被动机制的一个例子，完全不被理解。我将采用的方法将涉及建立一系列数学模型，以了解这种粘合剂是如何工作的。在这里，我将受益于小组中关于表面张力主导现象的现有专业知识，特别是当它适用于软对象的变形时。我还将确保我与沃尔特·费德勒团队和罗伯特·斯泰尔(材料科学，ETH-苏黎世)的实验者密切合作：这将使我能够开发与生物相关的模型(费德勒团队)，同时也能够在理想化的场景中执行定量测试(Rob Style)。这种数学技术的组合(渐近分析和一些数值技术)与来自生物和理想化系统的真实实验数据进行了测试，使这项研究既及时又新颖。该项目属于EPSRC流体动力学研究领域

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