EAGER: A Novel Experiment to Study Interfacial Processes between Droplet and Patterned Surfaces

Hsia CBET -1247512所提出的探索性EAGER项目旨在首次定量测量液滴和图案化基底之间的界面相互作用。一种新的实验技术的发展，定量研究的相互作用力作为一个功能的几何形状和缺陷特性的微图案。 该系统首次为不同几何和化学条件下的接触线钉扎等长期存在的界面过程理论提供了定量测试平台，从而使固态物理、表面化学和微加工等众多领域受益。 具有微图案的基底，特别是那些具有与小尺度液滴相互作用的微柱“森林”的基底，近年来因其多功能性和不寻常的特性（包括润湿性、粘附能、导电性或电容）而引起了极大的兴趣。 这些图案在依赖于非润湿表面的广泛工业过程中具有潜在的应用，所述非润湿表面拒绝污垢、具有低粘附能、拒绝水（例如挡风玻璃的涂层）、抵抗冷凝（例如在制冷装置中）或可用于气体的孔过滤（例如在微型燃料电池中）。 然而，对液滴形状和动力学的定量理解落后于大量的原理验证实验。 特别是，很少有人知道的图案和支柱的几何形状上的动态接触线运动和维持（或逮捕）这种运动所需的力量的影响。 拟议的工作将采用新的实验技术，同时定量测量液滴形状和接触线钉扎力，无论是在单缺陷水平的空间分辨率，并能够快速的时间分辨率。 孤立的缺陷与接触线的相互作用的定义形状长期以来一直是钉扎理论的主题，被视为一个理想化的描述真实的接触线的行为。 借助高速摄影和灵敏的力传感器，液滴和基底在相对运动中的力和变形将通过进行关键测量来同时确定，以准确描述动态接触角滞后以及液滴在疏水表面上的排斥、破碎和聚结。 这些实验可以访问和分析超出当前实验范围的各种速度，并且与应用程序高度相关。 EAGER的研究计划有以下目标：（1）在一个实验系统中寻求对接触线钉扎和孤立缺陷的脱钉的准确理解，该实验系统可以作为更广泛的界面过程背景下的缺陷钉扎的范例;（2）承认缺陷分布和缺陷相互作用对接触线整体的影响;（iii）探索一种创新的实验技术组合，有望改进一套工具，用于分析接触线运动的microscale. Broader影响拟议工作的更广泛的影响包括社会，群体和个人规模。 该研究为社会需求巨大的领域提供了基本见解：清洁水，制冷，能源和先进制造。 参与该项目的研究生和本科生将接受微细加工、软光刻、表面图案化和其他非常重要的工艺领域的培训。 PI还将在现有课程和演示中纳入研究成果。 PI计划通过积极参与几个校内/校外项目，包括工程项目中的女性，少数民族工程项目和麦克奈尔学者项目，来促进代表性不足的群体成员的参与。

Hsia CBET - 1247512The proposed exploratory EAGER project aims at the first quantitative measurement of interfacial interactions between a droplet and a patterned substrate. A novel experimental technique is developed to quantitatively study the interaction forces as a function of the geometry and defect characteristics of the micropatterns. The system provides a quantitative testbed for long-standing theories of interfacial processes such as contact-line pinning under different geometric and chemical conditions for the first time, thus benefitting a huge variety of fields, including solid state physics, surface chemistry, and microfabrication. Intellectual MeritSubstrates with micropatterns, particularly those with a "forest" of micropillars interacting with small-scale droplets, have garnered enormous interest in recent years for their versatility and unusual properties, including wettability, adhesive energy, conductivity or capacitance. These patterns have potential applications in widespread industrial processes that rely on non-wetting surfaces that reject dirt, have low adhesive energy, reject water (e.g. coatings for windshields), resist condensation (e.g. in refrigeration devices), or are useful in pore filtration of gases (e.g. in micro fuel cells). Nevertheless, a quantitative understanding of droplet shapes and dynamics lags behind a large number of proof-of-principle experiments. In particular, very little is known about the effect of pattern and pillar geometry on the dynamics of contact line motion and the forces needed to sustain (or arrest) such motion. The proposed work will apply novel experimental techniques for simultaneous quantitative measurements of droplet shape and contact-line pinning forces, both with a spatial resolution at the single-defect level and capable of fast time resolution. The interaction of isolated defects of defined shape with contact lines has long been the subject of pinning theories, perceived as an idealization of the description of real contact line behavior. With high-speed photography and sensitive force sensors, forces and deformations of droplets and substrates in relative motion will be determined simultaneously by making crucial measurements for an accurate description of dynamical contact angle hysteresis as well as droplet repulsion, fragmentation, and coalescence on hydrophobic surfaces. The experiments can access and analyze a wide range of speeds beyond current experiments, in a regime highly relevant for applications. The proposed EAGER research proposal has the following objectives: (i) to seek an accurate understanding of contact line pinning and depinning from isolated defects, in an experimental system that can serve as a paradigm for defect pinning in broader contexts of interfacial processes; (ii) to acknowledge the effect of defect distribution and defect interaction on the contact line as a whole; (iii) to explore an innovative combination of experimental techniques, promising an improved set of tools for analyzing contact line motion on the microscale.Broader ImpactsThe Broader Impacts of the proposed work include those on the societal, group, and individual scales. The research provides fundamental insight in fields of great societal need: clean water, refrigeration, energy, and advanced manufacturing. The graduate and undergraduate students involved in the project will be trained in the areas of microfabrication, soft lithography, surface patterning, and other processes that are of great importance. The PI will also incorporate research results in existing courses and demonstrations. The PI has plans in place to boost the participation of members from under-represented groups by proactively participating in several on-campus/off-campus programs, including Women in Engineering Program, the Minority Engineering Program, and the McNair Scholar Program.