Adhesion on rough surfaces and mechanisms of self-cleaning in insect attachment pads

胶带是由非常柔软和粘稠的材料制成的，使它们能够接触到中等粗糙的表面。因此，它们非常容易受到污染，只能使用一到两次。相比之下，在昆虫脚垫上发现的生物粘合剂可以很好地附着在粗糙和受污染的底物上；它们可以快速附着和分离数百万次，而不会损失粘附力。动物胶垫是新型仿生胶粘剂的重要模型，但其功能的重要方面仍未完全了解。在这个项目中，我们研究了昆虫粘合垫如何应对表面粗糙度和污染的机制。我们将使用透明微结构衬底作为工具来研究光滑和毛茸茸的昆虫粘合垫的性能。这些微结构由微米和纳米尺寸的柱子和脊子组成，将通过光学光刻和纳米压印来制造。与随机粗糙的表面不同，这些衬底具有明确的几何形状，可以让我们直观地看到附着在它们上面的昆虫垫的接触区。我们将改变表面结构的宽度、高度和间距，以探索粗糙表面的详细参数，这些参数可以通过光滑和毛茸茸的昆虫粘合垫来补偿。同时，我们将测量粗糙度对粘附力和摩擦力的影响，并确定限制昆虫粘附力的表面条件。我们将研究粗糙表面上的衬垫接触如何依赖于法向载荷和剪切力，以及与时间相关的粘弹性衬垫属性如何影响它。我们还将使用微结构底物来比较蟑螂身上两种类型的脚垫，这两种脚垫似乎专门用于粘合和摩擦(推动)，以测试它们在符合性和粘合强度方面是否有所不同。我们将研究天然粘合垫是如何通过测量用标准化颗粒污染垫后的力来进行自我清洁的。我们将测试三种可能的自清洁机制，即通过交替推拉运动来脱落颗粒，在粗糙表面上滑动时颗粒的互锁，以及通过分泌粘性液体来去除颗粒。我们对昆虫在粗糙表面和污染表面的粘附性的研究不仅对仿生粘合剂的开发具有重要意义，而且对于开发用于害虫防治的光滑涂料也具有重要意义。

Adhesive tapes are made of very soft and tacky materials, allowing them to make contact to moderately rough surfaces. As a result, they are highly susceptible to contamination and can only be used once or twice. By contrast, biological adhesives, as found on the foot pads of insects, allow strong adhesion to rough and contaminated substrates; they can rapidly attach and detach millions of times with no loss of adhesive power. Animal adhesive pads are important models for new 'biomimetic' adhesives, but important aspects of their function are still not fully understood. In this project, we investigate the mechanisms of how insect adhesive pads can cope with surface roughness and contamination. We will use transparent microstructured substrates as a tool to investigate the performance of smooth and hairy adhesive pads of insects. These microstructures consist of micron- and nanometre-sized pillars and ridges and will be fabricated by optical lithography and nanoimprinting. Unlike randomly rough surfaces, these substrates have a well-defined geometry and will allow us to visualize the contact zones of insect pads adhering to them. We will vary the width, height and spacing of the surface structures to explore the detailed parameters of rough surfaces that can be compensated by smooth and hairy adhesive pads of insects. At the same time we will measure what effect roughness has on adhesion and friction forces and we will identify surface conditions that limit insect adhesion. We will study how the pad contact on rough surfaces depends on normal load and shear forces and how it is influenced by time-dependent viscoelastic pad properties. We will also use microstructured substrates to compare two types of foot pads in cockroaches that appear specialized for adhesion and friction (pushing), to test whether they differ in conformability and adhesive strength. We will investigate how natural adhesive pads are able to self-clean by measuring forces after contaminating the pads with standardised particles. We will test three possible mechanisms for self-cleaning, the shedding of particles by alternating pushing and pulling movements, the interlocking of particles when sliding on rough surfaces, and the removal of particles via the secretion of adhesive fluid. Our study of insect adhesion on rough and contaminated surfaces will be important not only for the development of biomimetic adhesives but also for the development of slippery coatings for insect pest control.