CBET-EPSRC Dynamic Wetting & Interfacial Transitions in Three Dimensions: Theory vs Experiment

液体在固体物体上扩散是一种常见的现象，每天都在发生。例如：雨滴砸在挡风玻璃上；石头被扔进池塘；草莓外面裹着巧克力喷泉。在所有这些情况下，液体可以通过（或“湿”）物体的最大速度，超过这个速度会产生很容易观察到的效果，例如雨滴分解成更小的水滴或草莓的斑块涂层。值得注意的是，尽管这些日常现象看似无害，但目前还没有理论或计算模型能够预测并因此控制润湿的最大速度。除了对这些事件的学术好奇心外，它们还构成了一系列显著的技术应用和自然过程的基础。特别是，随后固化的薄层液体涂层是一个价值约1000亿美元（而且还在不断增加）的市场，这是制造从太阳能电池到缓解能源和环境危机到新兴印刷电子电路能力等产品的关键。在这些行业中，创造最佳设计的能力目前受到我们对基础物理知识的限制。该项目将通过利用软件中嵌入的计算模型和前沿实验分析之间的协同作用，支持对上述现象的探索和行业内的创新。计算和实验方面尤其雄心勃勃，因为(a)固体润湿是一个强烈的多尺度问题，需要从几乎分子尺度到工程应用尺度的解决方案，(b)该过程本质上是三维的，这意味着简化导致计算复杂性的降低是不可能的，必须实施高性能计算技术。本项目利用调查人员在(a)方面的最新进展，首次解决与(b)有关的问题。关于液体如何在固体表面上扩散的新知识最初将集中在工业涂层问题上，其中的挑战是在不携带空气的情况下尽可能快地用液体湿润固体。最初的进展将在与3M公司（以便利贴和scotchard等产品而闻名）的合作中得到指导和加强。3M公司是一家跨国公司，生产太阳能电池、油漆、防反射涂料和粘合剂等，年销售额约为300亿美元。对于他们来说，计算模型提供了一种快速和经济有效的方法来理解在起作用的物理机制，以优化涂层过程。本项目取得的突破将对相关研究领域产生影响。在行业内，这包括与Trijet合作，Trijet是一家领先的新兴液滴技术咨询公司，他们将把我们的进步转化为改进喷墨打印技术的控制，这些技术正在用于日常流体应用，例如汽车工业和印刷电子产品的高价值金属油墨（如银）的印刷。此外，我们的进步可能会对其他领域产生影响，比如气候科学，在气候科学中，当液滴撞击同一液体的浴缸时，可以观察到类似的流动结构，就像雨滴撞击海洋一样。在这里，我们对液滴和海洋之间的气体如何被带入后者的理解可以用于气候模型，这是一个关键参数。

The spreading of liquids over solid objects is a familiar and every day occurrence. For example: raindrops smashing into windscreens; stones being thrown into ponds; a chocolate fountain coating a strawberry. In all these cases, there is a maximum speed at which the liquid can traverse (or 'wet') the object and going beyond this speed creates easily observable effects such as the the disintegration of the raindrop into smaller drops or a patchy coating of the strawberry. Remarkably, despite the seemingly innocuous nature of these everyday phenomena, at present there exists no theory or computational model capable of predicting, and hence controlling, the maximum speed of wetting.In addition to the academic curiosity of these events, they form the basis of a remarkable array of technological applications and natural processes. In particular, the coating of thin layers of liquid which subsequently solidify is a ~$100 billion (and ever-increasing) market which is key to the manufacture of products ranging from solar cells, to alleviate energy and environmental crises, to emerging capabilities to print electronic circuits. In these industries, an ability to create optimal designs is currently limited by our knowledge of the underlying physics. This project will underpin exploration of the aforementioned phenomena and innovation within industry by exploiting a synergy between computational models embedded within software and cutting-edge experimental analysis. The computational and experimental aspects are particularly ambitious as (a) the wetting of solids is a strongly multiscale problem, requiring resolution from almost-molecular scales right up to engineering application scales, and (b) the process is inherently three-dimensional, meaning that simplifications leading to reductions in computational complexity are impossible and high performance computing techniques must be implemented. This project exploits recent advances in (a), by the Investigators, in order to tackle the problems associated with (b) for the very first time.New knowledge of how liquids spread over solid surfaces will be initially focussed on industrial coating problems, where the challenge is to wet a solid with a liquid as fast as possible without entraining air. Initial progress will be guided and enhanced by a collaboration with 3M (famous for products such as Post-it and Scotchgard), a multinational corporation with ~$30 billion sales annually from manufacturing solar cells, paints, anti-reflective coatings, adhesives, etc. For them, a computational model provides a fast and cost-effective way to achieve understanding of the physical mechanisms at play in order to optimise the coating process. Breakthroughs achieved in this project will have impact within related fields of research. Within industry, this involves working with Trijet, a leading consulting firm on emerging drop-based technologies, who will translate our advances to improve the control of inkjet printing technologies that are being used in everyday applications of fluids, e.g. in the automotive industries and in the printing of high-value metallic inks such as silver for printed electronics. Furthermore, our advances could have impact in other fields, such as climate science, where similar flow structures are observed when a liquid drop impacts a bath of the same liquid, as occurs when a raindrop impacts the ocean. Here, our understanding of how trapped gas between the drop and the ocean is entrained into the latter could feed into climate models, where this is a key parameter.