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

提出的探索性EAGER项目旨在首次定量测量液滴和图案衬底之间的界面相互作用。本文提出了一种新的实验方法来定量研究微图案几何形状和缺陷特征对相互作用力的影响。该系统首次为长期存在的界面过程理论提供了定量测试平台，例如在不同几何和化学条件下的接触线钉接，从而受益于各种领域，包括固态物理，表面化学和微制造。具有微图案的衬底，特别是那些具有与小液滴相互作用的微柱“森林”的衬底，近年来因其多功能性和不寻常的特性（包括润湿性，粘接能，导电性或电容）而引起了极大的兴趣。这些图案在广泛的工业过程中有潜在的应用，这些工业过程依赖于不湿润的表面，这些表面拒绝污垢，具有低粘附能，拒绝水（例如挡风玻璃涂层），抵抗冷凝（例如在制冷装置中），或者在气体的孔隙过滤（例如在微型燃料电池中）中有用。然而，对液滴形状和动力学的定量理解落后于大量的原理证明实验。特别是，关于图案和柱的几何形状对接触线运动的动力学的影响以及维持（或阻止）这种运动所需的力，我们所知甚少。提出的工作将应用新颖的实验技术来同时定量测量液滴形状和接触线钉住力，既具有单缺陷水平的空间分辨率，又具有快速的时间分辨率。确定形状的孤立缺陷与接触线的相互作用长期以来一直是钉钉理论的主题，被认为是对真实接触线行为描述的理想化。通过高速摄影和灵敏的力传感器，通过对动态接触角滞后以及疏水表面上的液滴排斥、破碎和聚并进行精确描述的关键测量，可以同时确定相对运动中的液滴和基底的力和变形。实验可以访问和分析超出当前实验的大范围速度，在一个与应用高度相关的制度。拟议的EAGER研究计划有以下目标：(i)在一个实验系统中，寻求对孤立缺陷的接触线钉住和脱钉的准确理解，该实验系统可以作为更广泛的界面过程中缺陷钉住的范例；（ii）承认缺陷分布和缺陷相互作用对整个接触线的影响；（iii）探索实验技术的创新组合，有望在微观尺度上改进一套分析接触线运动的工具。更广泛的影响拟议工作的更广泛的影响包括对社会、群体和个人的影响。这项研究为清洁水、制冷、能源和先进制造业等重大社会需求领域提供了基本见解。参与该项目的研究生和本科生将在微加工、软光刻、表面图案和其他非常重要的工艺领域接受培训。PI还将把研究成果纳入现有的课程和示范。PI计划通过积极参与一些校内/校外项目，包括女性参与工程项目、少数族裔工程项目和麦克奈尔学者项目，来促进代表性不足群体成员的参与。

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.