Interfacial instabilities in fluid films

在各种情况下，具有自由表面覆盖在固体材料(衬底)上的薄流体薄膜经常出现。在工业环境中，它们用于涂层和保护表面，或促进质量和热量的传递。在生物体中，它们发挥着至关重要的功能，例如，覆盖眼睛的泪膜或肺部呼吸道的液体衬里。在环境中也会遇到流体膜，例如地下水渗透到非饱和裂隙岩石中。其他例子是熔岩流动和冰川动力学，它们与长度小得多的流体膜受相同的物理机制支配。流体薄膜容易受到界面不稳定的影响，在一定条件下，流动会发展，导致薄膜厚度不均匀。随着时间的推移，界面不稳定会导致薄膜破裂，如果流动足够快，大振幅波可以形成并沿表面传播。界面不稳定的出现通常会对流体膜的预期功能产生不利影响。例如，在与制造工艺相关的涂布应用中，不均匀的薄膜流动可能导致涂布材料的不规则分布。同样，具有生物功能的流体膜如果变得太薄或形成孔洞，可能会无效。然而，在某些工业部门，界面不稳定可以优化这一过程。例如，在热交换器和质量交换器中，由于液-气界面的表面积增加，界面波的形成改善了设备的运行，从而促进了传输。数学流体流动模型可用于预测不稳定开始的条件和预测其演变。我建议建立理论模型，研究影响流体薄膜稳定性的各种因素在实际情况下的综合影响。要考虑的显著因素包括热效应、表面活性剂(影响表面张力的化学溶质)的存在、流体通过多孔衬底的渗透以及具有起伏或波纹的非平面表面的衬底。

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.