ISS: Inertial Spreading and Imbibition of a Liquid Drop Through a Porous Surface

拟议的研究将利用国际空间站（ISS）的微重力环境来提高对吸吮的理解，吸吮是一种水被固体吸收的过程。一组毛细血管将被用作实验装置，用于研究当液体润湿毛细血管时接触线的钉住和去钉住。在国际空间站进行实验的原因是，利用太空中没有重力时增加的这些现象的长时间尺度，因此测量分辨率远高于地球。渗吸过程在许多工程和工业过程中都很重要。例如，了解固体和液体如何相互作用，可以大大改善洪水控制，据估计，这每年可带来110亿美元的收益。这项工作的另一个工程应用是湿造粒过程，这是制药公司用于药物制造的重要过程。pi建议利用国际空间站上的OASIS设施，在时间和长度尺度上观察水进入特征良好的圆柱形毛细血管的吸附性，以观察迄今为止在地球重力下无法观测到的细节。该数据集将用作验证复杂毛细管几何形状的数值模拟的基准。当一滴水滴接触到多孔介质时，它就像铺在一个复合表面上一样扩散开来。表面首先表现为疏水材料，因为液体必须穿过充满空气的孔隙。当接触建立时，一些液体被毛细吸进孔中，毛细受到黏性力的阻力，黏性力随吸收区域的长度而增长。这一过程总是从惯性状态开始，由于运动和可能在新湿润的毛细血管上跳跃的气-液-固接触线的固定而变得复杂。一个问题是，模拟是否捕捉到了如此关键的微妙之处。为了研究地球上的吸胀，必须缩小时间和距离，以减轻重力引起的扭曲。这些小尺度使得不可能详细观察惯性和固定过程。相反，OASIS将缓慢地挤压水球，直到它们接触到毛细管板。它们的直径为12mm，足以让GX1050C相机看到单个毛细血管附近的细节，并且足够长，可以观察整个吸吸过程的动力学。为了研究接触钉住的作用，提出了用十种金属多孔毛细板进行自组装单层（SAM）处理来测试基体，从而将前进和后退接触角固定在已知值。这些详细的观测结果将与晶格玻尔兹曼和直接数值模拟进行对比。原型测试将在康奈尔大学的1.2s自由落体塔进行，塔上有一种独特的机制，可以产生相对较大的水球。多孔表面的润湿是三种物质共存状态应用的核心，如燃料电池、过滤、二氧化碳封存、热管或土壤润湿。这些系统的性能由毛细力、接触角施加的几何约束和接触角滞后决定。渗吸可能是有害的（例如，水渗入后土坝坍塌），也可能是有益的（例如，灌溉或药物辅料生产中的湿造粒）。这项工作将由本科生和一名博士生进行。此外，还将加强2000年由公团创立的一所地方中学的技术教育外展项目。

PI: Louge, MichelProposal Number: 1637531The proposed research will utilize the microgravity environment on the International Space Station (ISS) to improve understanding of imbibition, a process in which water is absorbed by solids. An array of capillaries is going to be used as the experimental set up for investigating contact line pinning and de-pinning as a liquid wets the capillaries. The reason for conducting experiments at the ISS is to take advantage of the long time scales for these phenomena that increases when there is no gravity in space, so that the measurement resolution is much higher than on Earth. The imbibition process is important to many engineering and industrial processes. For example, understanding of how solids and liquids interact, can lead to major improvements in flooding control, which is estimated to cause $11 billion annually. Another engineering application of this work is the process of wet granulation, an important process used by pharmaceutical companies for drug manufacturing. The PIs propose to exploit the OASIS facility on the ISS to observe the imbibition of water into well-characterized cylindrical capillaries on time and length scales long enough to observe details hitherto inaccessible under Earth gravity. The data set will be used as a benchmark for validating numerical simulations on complex capillary geometry. When a drop touches a porous medium, it spreads as if laid on a composite surface. The surface first behaves as a hydrophobic material, as liquid must penetrate pores filled with air. When contact is established, some of the liquid is drawn into pores by a capillarity that is resisted by viscous forces growing with length of the imbibed region. This process always begins with an inertial regime that is complicated by the motion and possible pinning of gas-liquid-solid contact lines jumping over newly-wetted capillaries. A question is whether simulations capture such crucial subtleties. To study imbibition on Earth, time and distance must be shrunk to mitigate gravity-induced distortion. These small scales make it impossible to observe inertial and pinning processes in detail. Instead, OASIS will slowly extrude water spheres until they touch the capillary plate. Their 12mm diameter will be large enough for the GX1050C camera to visualize details near individual capillaries, and long enough to observe dynamics of the entire imbibition process. To investigate the role of contact pinning, it is proposed to test a matrix with ten kinds of porous capillary plates made of metal treated with Self-Assembled Monolayers (SAM), thereby fixing advancing and receding contact angles at known values. These detailed observations will be contrasted with lattice-Boltzmann and Direct Numerical simulations. Prototype testing will take place at Cornell's 1.2s free-fall tower with a unique mechanism producing relatively large water spheres. The wetting of porous surfaces is central to applications where three states of matter coexist, such as fuel cells, filtration, CO2 sequestration, heat pipes, or the wetting of soils. Performance of these systems is determined by capillary forces, geometrical constraints imposed by the contact angle, and contact angle hysteresis. Imbibition can be detrimental (e.g., earth dam collapse after water infiltration), or useful (e.g., irrigation, or wet granulation in drug excipient manufacture). This work will be conducted with undergraduates and a doctoral student. It will also strengthen an outreach program to Technology Education at a local Middle School, which the PI created in 2000.