EAGER: Microscale Fingering Instabilities in Drying Colloid and Polymer Films

EAGER：干燥胶体和聚合物薄膜中的微尺度指法不稳定性

• 批准号: 1936541
• 负责人: James Gilchrist
• 金额: $ 18.56万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1936541&HistoricalAwards=false
• 关键词: EAGER; Microscale; Fingering; Instabilities; Drying

When a viscous fluid such as oil is trapped within a porous material like soil or sand, it is very difficult to remove. Trying to displace the trapped oil by forcing air into the material fails, because the lower viscosity air will penetrate through the higher viscosity oil. The air will form long fingers into the oil, leaving most of the oil behind. This visually striking process, known as the Saffman-Taylor instability, has been well documented in macroscopic systems. It strongly affects oil recovery processes for energy production and environmental remediation. In a serendipitous discovery, fingers were found in drying films of nanoparticles and polymer, similar to that found in paints used on buildings, cars, and many other consumer goods. What is surprising is that these fingers form at much smaller scales, and they do not follow the rules determined for the Saffman-Taylor instability. This project will investigate how the physics surrounding the formation of these microscopic fingers differs from macroscale phenomena. This fingering instability will be characterized quantitatively in well-controlled experiments and computational analysis of images obtained using specialized microscopy. The knowledge gained will be used to control or suppress the formation of fingers in order to alter the properties of these films. These fingers may be ubiquitous in drying thin films of particles in viscous liquids and may have a strong impact of the adhesion of these films to their substrates.This research will investigate a visually striking fluid flow instability in colloid-polymer thin films during drying that was found using high-speed confocal laser scanning microscopy. This is the first observation of a fingering instability of polymer solutions at micron or sub-micron length scales in porous materials such as colloidal crystals. Fingering instabilities, such as the Saffman-Taylor instability, have had broad impacts for transport in porous media for secondary oil recovery and aquifer transport. Most studies of the Saffman-Taylor instability focus on the displacement of one higher viscosity Newtonian fluid with an immiscible lower viscosity Newtonian fluid in either a Hele-Shaw cell or a porous material. Fingers in this study are not visible using regular light microscopy because they have wavelengths on the micron scale, defying the typical Saffman-Taylor scaling found in macroscopic systems. This project will investigate the modes of this instability across various polymer concentrations, polymer molecular weights, and particle sizes where the polymer radius of gyration ranges from very small to that which is comparable to the pore scale of colloidal crystals. The goal is to determine whether this fingering instability differs from previous studies due to the non-Newtonian behavior or the interfacial properties of the fluid at the nanoscale. Because the polymer is left behind, it forms well-defined solid structures at the film-substrate interface. These structures will be investigated and utilized in the fabrication of nanoscale or microscale networks of fluid channels for devices. Moreover, the fingering instability may have a significant effect on film adhesion to the substrate through reduction of contact area and/or creating microfibrillated structures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

当像油这样的粘性流体被困在土壤或沙子等多孔材料中时，很难将其清除。试图通过迫使空气进入材料来取代被困的石油的努力失败了，因为较低粘度的空气将穿透较高粘度的石油。空气会形成长长的手指进入油中，把大部分油留在后面。这种引人注目的过程，被称为萨夫曼-泰勒不稳定性，已经在宏观系统中得到了很好的记录。它强烈影响用于能源生产和环境修复的石油开采过程。在一个偶然的发现中，在纳米颗粒和聚合物的干燥薄膜中发现了手指，类似于在建筑、汽车和许多其他消费品上使用的涂料中发现的手指。令人惊讶的是，这些手指形成的尺度要小得多，它们并不遵循为萨夫曼-泰勒不稳定性确定的规则。这个项目将研究围绕这些微观手指形成的物理如何与宏观尺度现象不同。这种指法不稳定性将在良好控制的实验和使用特殊显微镜获得的图像的计算分析中得到定量表征。所获得的知识将被用来控制或抑制手指的形成，以便改变这些薄膜的性质。在干燥粘性液体中的颗粒薄膜时，这些手指可能是普遍存在的，并可能对这些薄膜与其衬底的粘附性产生强烈的影响。本研究将利用高速共聚焦激光扫描显微镜来研究在干燥过程中胶体聚合物薄膜中明显的流体流动不稳定性。这是首次观察到聚合物溶液在微米或亚微米尺度上在多孔性材料(如胶体晶体)中的指进不稳定性。指进不稳定性，如萨夫曼-泰勒不稳定性，对在多孔介质中进行二次采油和含水层运移产生了广泛的影响。关于Saffman-Taylor不稳定性的研究大多集中在一种较高粘度的牛顿流体与一种不相容的低粘度牛顿流体在Hele-Shaw腔体或多孔材料中的驱替。这项研究中的手指在常规光学显微镜下是不可见的，因为它们的波长在微米级，这与宏观系统中发现的典型的萨夫曼-泰勒标度不符。这个项目将研究不同聚合物浓度、聚合物相对分子质量和颗粒大小的这种不稳定性的模式，其中聚合物的旋转半径从非常小的范围到与胶体晶体的孔尺度相当的范围。我们的目标是确定这种指进不稳定性是否与以前的研究不同，这是由于流体在纳米尺度上的非牛顿行为或界面属性。由于聚合物被留在了后面，它在薄膜-衬底界面形成了明确的固体结构。这些结构将被研究并用于制造用于设备的纳米或微米尺度的流体通道网络。此外，指法不稳定性可能会通过减少接触面积和/或创建微纤化结构对薄膜与基材的附着力产生重大影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Chemical vs. mechanical microstructure evolution in drying colloid and polymer coatings

• DOI: 10.1038/s41598-020-66875-0
• 发表时间: 2020-06
• 期刊: Scientific Reports
• 影响因子: 4.6
• 作者: Thitiporn Kaewpetch;J. Gilchrist