Wetting of Elastic Fibres: A Novel Immersed Boundary-Lattice Spring-Lattice Boltzmann Simulation Approach

纤维结构是一种用途广泛的材料。它们在自然界中含量丰富，如在羽毛、毛发、蜘蛛网和昆虫粘合垫中观察到的那样。它们在工程系统中也被广泛利用，从我们熟悉的纸张和纺织品的例子，到高精度的微型和纳米技术。对于许多纤维材料来说，它们与液体的相互作用是至关重要的。由于纤维的尺寸很小，毛细作用(如在植物吸收液体时观察到的)通常起主导作用。此外，毛细作用使纤维变形，由于弹性而产生相反的力。这种弹性和毛细之间的竞争-弹性毛细-在广泛的应用中发现了它的相关性，包括液体在湿巾和尿布中的渗透，以及昆虫眼睑中的毛发和海洋鸟类羽毛中的小羽枝的聚集。尽管在自然界中有许多工业应用和常见的情况，但我们对湿纤维的弹性毛细血管反应的了解仍然非常有限。最近的实验表明，纳米结构中的图案形成可以通过弹性-毛细血管动力学来操纵；与杀虫剂或除草剂等应用相关的液滴及其飞溅的捕获取决于纤维的几何形状和灵活性。这些只是许多弹性-毛细血管现象中的一小部分，研究已经成熟，特别是使用计算机模拟，因为纤维几何、弹性和毛细之间的复杂相互作用迅速使分析处理变得困难。遗憾的是，目前还没有能够捕捉固体变形、液体流动和毛细管力的模拟方法。因此，我在这个项目中的目标是提供一个能够应对这样一个挑战的数字平台。这个项目植根于我最近在润湿现象模拟技术方面的研究进展。作为原理的证明，为了证明新方法可以捕捉软材料上的润湿动力学，我将研究小液滴在两个彼此成不同角度取向的弹性纤维上的传播，并将研究在重力等体力的作用下这些液滴的去除。这些都是理解天然和合成湿纤维组件的排列和清洁性能的范例。我的新模拟将根据宝洁提供的实验数据进行验证，其中弹性纤维的润湿与其许多产品相关，从吸附材料(包括尿布和湿巾)到个人卫生产品(例如洗发水和洗衣粉)。如果成功，我的新方法将开辟一条前所未有的途径来模拟嵌入复杂几何结构的静态和动态弹性毛细血管现象。因此，它将促进我们对弹性毛细管的理解，并帮助将基本的科学见解引导到实际应用的设计原则中。

Fibrous structures are versatile materials. They are abundant in nature, as observed in feathers, hairs, spider webs and adhesive pads of insects. They are also widely exploited in engineered systems, from the familiar examples of papers and textiles to high-precision micro- and nano-technologies. For many fibrous materials, their interaction with liquids is of paramount importance. Due to the small size of the fibres, capillary action (as observed e.g. in the drawing up of liquids in plants) often plays the dominant role. Furthermore, the action of capillarity deforms the fibres, which results in an opposing force due to elasticity. This competition between elasticity and capillarity - elastocapillarity - finds its relevance in a wide range of applications, including liquid penetration in wipes and nappies, and the clumping of hairs in the tarsi of insects and of barbules in marine bird feathers.Despite the numerous industrial applications and common occurrence in nature, our understanding of elastocapillary response of wet fibres is still very limited. Recent experiments suggest that pattern formation in nanostructures can be manipulated by elastocapillary dynamics; the capture of drops and their splashing, of relevance to the application of pesticides or herbicides among others, depend on the fibre geometry and flexibility. These are just a few of many elastocapillary phenomena ripe for investigations, especially using computer simulations, since the intricate interplay between fibre geometry, elasticity and capillarity quickly makes analytical treatments intractable. Unfortunately, simulation methods that can capture solid deformation, flow of liquids, and capillary forces are currently not available. Thus, it is my aim in this project is to deliver a numerical platform able to tackle such a challenge. This project is rooted in my recent research advances in simulation techniques for wetting phenomena. As a proof of principle, to demonstrate that the novel method can capture wetting dynamics on soft materials, I will examine the spreading of small droplets on two elastic fibres oriented at various angles with respect to each other, and I will study the removal of these droplets under the action of a body force such as gravity. These are paradigmatic examples for understanding the arrangement and cleaning properties of natural and synthetic wet fibre assemblies.My new simulations will be validated against experimental data provided by Procter and Gamble, where wetting of elastic fibres is relevant for many of their products, ranging from adsorbent materials (including nappies and wipes) to personal hygiene products (e.g. shampoos and laundry detergents).If successful, my novel approach will open an unprecedented route to model static and dynamic elastocapillary phenomena embedded in complex geometries. As such, it will advance our understanding of elastocapillarity, and help channel fundamental scientific insights into design principles for practical applications.