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.

当油等粘性流体被困在土壤或沙子等多孔材料中时，很难去除。 尝试通过将空气压入材料中来置换滞留的油会失败，因为较低粘度的空气会渗透较高粘度的油。 空气会形成长手指进入油中，留下大部分油。 这种视觉上引人注目的过程被称为萨夫曼-泰勒不稳定性，在宏观系统中已得到充分记录。 它强烈影响能源生产和环境修复的石油回收过程。 在一次偶然的发现中，人们在纳米颗粒和聚合物的干燥薄膜中发现了手指，这与建筑物、汽车和许多其他消费品上使用的油漆中发现的类似。 令人惊讶的是，这些手指形成的尺度要小得多，而且它们不遵循萨夫曼-泰勒不稳定性确定的规则。 该项目将研究围绕这些微观手指形成的物理现象与宏观现象有何不同。 这种指法不稳定性将在良好控制的实验和使用专门显微镜获得的图像的计算分析中进行定量表征。 获得的知识将用于控制或抑制指状物的形成，以改变这些薄膜的特性。 这些指状结构在干燥粘性液体中的颗粒薄膜时可能无处不在，并且可能对这些薄膜与其基材的粘附力产生强烈影响。这项研究将研究使用高速共焦激光扫描显微镜发现的干燥过程中胶体聚合物薄膜中视觉上引人注目的流体流动不稳定性。 这是首次观察到胶体晶体等多孔材料中微米或亚微米长度尺度的聚合物溶液的指指不稳定性。 指状不稳定性，例如萨夫曼-泰勒不稳定性，对二次采油和含水层运输的多孔介质中的运输产生了广泛的影响。 大多数关于萨夫曼-泰勒不稳定性的研究都集中在一种较高粘度牛顿流体与一种不混溶的较低粘度牛顿流体在赫勒-肖池或多孔材料中的置换。 这项研究中的手指在常规光学显微镜下是不可见的，因为它们的波长为微米级，这违背了宏观系统中典型的萨夫曼-泰勒尺度。 该项目将研究不同聚合物浓度、聚合物分子量和颗粒尺寸的这种不稳定性模式，其中聚合物回转半径范围从非常小到与胶体晶体的孔隙规模相当。 目标是确定这种指法不稳定性是否由于非牛顿行为或纳米级流体的界面特性而与之前的研究不同。 由于聚合物被留下，它在薄膜-基材界面处形成明确的固体结构。 这些结构将被研究并用于制造设备的纳米级或微米级流体通道网络。 此外，指状不稳定性可能会通过减少接触面积和/或创建微纤丝结构对薄膜与基材的粘附力产生重大影响。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值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