Engineering and control of surfactant-laden flows: multi-scale analysis and experiments

在过去的二十年里，表面活性剂作为润湿剂的使用受到了极大的关注，因为它们在各种工业和生物医学应用中的重要性和潜力(涂层流动、去污、提高石油回收、治疗呼吸窘迫综合征)。尽管在该领域进行了研究，但仍然存在许多基本的悬而未决的问题，因为没有单一的方法(实验、模拟或理论)能够孤立地探索两亲分子在溶液中的流固行为的巨大复杂性。该项目将详细了解表面活性剂在接触线上的行为和在界面上的吸附，以及这最终如何影响疏水表面的扩散和润湿。在这种背景下，即使是听起来微不足道的问题也没有从根本上得到理解。例如，尽管不含表面活性剂的液滴在疏水基质上的平衡状态很容易用Young方程来表征，但当液滴中含有表面活性剂时就不是这样了。表面活性剂的分布是如何平衡的，由它引起的应力如何与接触线上的力平衡？后者是如何受表面活性剂的溶解性以及在高表面活性剂浓度下形成表面活性剂聚集体的影响的？这些问题是突出的和技术上重要的但难以避免的效果的基础，例如超扩散，即含有超级扩散表面活性剂(例如三硅氧烷)的水滴迅速扩散，在疏水基质上产生完美的润湿。这项建议的目的是将三个世界领先的集团聚集在一起，以协作、系统、多学科和多规模的方式解决这些根本问题。化学和分子相互作用需要在分子水平上进行详细的建模：EAM带来了这方面的专业知识。然后，这必须扩大到液滴和应用本身的长度：RVC和OKM在模拟表面活性剂梯度(Marangoni)驱动的流动方面有相当多的背景。这个问题需要对现象有新的物理化学理解，所开发的模型必须得到验证，而且确实需要详细而仔细的实验来提供信息：VMS在这两方面都处于世界领先地位。通过拟议的变革性研究将实现对表面活性剂流动的深入了解，这不仅将用于提供对这些流动的准确和可靠的预测，还将用于合理设计定制的表面活性剂分子结构，用于从农用化学品到提高石油采收率的各种应用。

Over the past two decades, the use of surfactants as wetting agents has enjoyed considerable attention due to their importance and potential in a variety of industrial and biomedical applications (coating flows, detergency, enhanced-oil-recovery, treatment of respiratory distress syndrome). Despite the research in the area, numerous fundamental open problems remain, as no single approach (experiments, simulations or theory) in isolation is able to probe the formidable complexities of the fluid-solid behaviour of amphiphilic molecules in solution. This project will provide detailed understanding of how surfactants behave at contact lines and adsorb at interfaces, and how this ultimately affects the spreading and wetting of hydrophobic surfaces. In this context, even trivial-sounding problems are not fundamentally understood. For instance, although the equilibrium state of a surfactant-free droplet on a hydrophobic substrate is easily characterised using the Young equation, this is not the case when the droplet is laden with surfactant. How does the surfactant distribution equilibriate and the stresses induced by it balance with the forces at the contact line? How are the latter influenced by surfactant solubility, and the formation of surfactant aggregates at high surfactant concentrations? These questions underlie striking and technologically important, yet poorly eludicated effects, such as superspreading whereby aqueous droplets containing superspreader surfactants (e.g. trisiloxanes) spread rapidly to produce perfect wetting over hydrophobic substrates. The purpose of this proposal is to draw together three world-leading groupings to tackle these fundamental problems in a collaborative, systematic, multi-disciplinary and multi-scale manner. The chemistry and molecular interactions require detailed modelling on the molecular level: EAM brings this expertise. This must then be scaled up to the lengthscale of droplets and the application itself: RVC and OKM have considerable background in modelling surfactant-gradient (Marangoni) driven flows. The problem requires new physicochemical understanding of the phenomena and the developed models must be validated, and indeed informed by, detailed and careful experiments: VMS is a world-leader in both. The deep knowledge of surfactant-laden flows that will be achieved via the proposed, transformative research will be used not only to provide accurate and reliable predictions of these flows but also to rationally design bespoke surfactant molecular architectures for various applications ranging from agrochemicals to enhanced-oil-recovery.