Interfacial instabilities in fluid films

具有覆盖固体材料（基底）的自由表面的薄流体膜经常出现在各种情况下。在工业环境中，它们用于涂覆和保护表面或促进质量和热量的传递。在生物体中，它们执行重要功能，例如，覆盖眼睛的泪膜或肺部气道的流体衬里。在环境中也会遇到流体膜，例如地下水渗透非饱和裂隙岩石。其他例子是熔岩流和冰川动力学，它们与长度尺度短得多的流体膜一样，受到相同的物理机制的控制。流体膜易受界面不稳定性的影响，在某种意义上，在某些条件下，流动将发展，导致膜厚度的不均匀性。随着时间的推移，界面不稳定性可能导致膜的破裂，并且如果流动足够快，则可以形成大幅度的波并沿表面沿着传播。界面不稳定性的出现通常对流体膜的预期功能具有不利影响。例如，在与制造工艺相关的涂层应用中，不均匀的膜流会导致涂层材料的不规则分布。类似地，如果流体膜变得太薄或形成孔，则用于生物功能的流体膜可能是无效的。然而，在某些工业部门，界面不稳定性可以优化该过程。例如，在热交换器和质量交换器中，界面波的形成改善了装置的操作，这是由于液-气界面的表面积增加的事实，这有利于输送。数学流体流动模型可用于预测不稳定性开始的条件并预测其演变。我建议实施的理论模型，将调查的各种因素的综合影响的稳定性的流体膜，在现实世界的情况下是相关的。值得注意的因素包括热效应、表面活性剂（影响表面张力的化学溶质）的存在、流体通过多孔基材的渗透以及具有呈现起伏或波纹的非平面表面的基材。

Thin fluid films with a free surface overlying a solid material (substrate) occur frequently in a variety of situations. In industrial settings they serve to coat and protect surfaces or facilitate the transfer of mass and heat. In living organisms they perform vital functions as does, for example, the tear film covering the eye or the fluid lining of airways in the lungs. Fluid films are also encountered in the environment, such as groundwater permeating unsaturated fractured rock. Other examples are lava flows and glacial dynamics which are governed by the same physical mechanisms as fluid films with much shorter length scales. Fluid films are subject to interfacial instability, in the sense that, under certain conditions, a flow will develop resulting in non-uniformity in the thickness of the film. In time, interfacial instability can lead to the rupture of the film, and if the flow is sufficiently fast, large amplitude waves can form and propagate along the surface. The appearance of interfacial instability often has an adverse effect on the intended function of the fluid film. In coating applications connected to manufacturing processes, for example, a nonuniform film flow can result in an irregular distribution of the coating material. Similarly, fluid films serving a biological function can be ineffective if they become too thin or develop holes. In certain industrial sectors, however, interfacial instability can optimize the process. For example, in heat and mass exchangers the formation of interfacial waves improves the operation of the device due to the fact that there is an increase in the surface area of the liquid-gas interface, which facilitates the transport. A mathematical fluid flow model can be used to anticipate the conditions for the onset of instability and predict its evolution. I propose to implement theoretical models that will investigate the combined effect of various factors affecting the stability of a fluid film that are relevant in real-world situations. Notable factors that will be considered include thermal effects, the presence of surfactants (chemical solutes affecting surface tension), the permeation of fluid through a porous substrate, as well as substrates with nonplanar surfaces exhibiting undulations or corrugations.