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

HSIA CBET-1247512拟议的探索性EIGER项目旨在首次定量测量液滴和图案化衬底之间的界面相互作用。发展了一种新的实验技术来定量研究相互作用力与微图形的几何和缺陷特征的函数关系。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一个定量的试验台，从而使包括固体物理、表面化学和微制造在内的许多领域受益。智力价值具有微图案的衬底，特别是那些具有微柱与小规模液滴相互作用的“森林”的衬底，近年来因其多功能性和特殊的性质而引起了极大的兴趣，包括润湿性、粘附性、导电性或电容。这些图案在广泛的工业过程中有潜在的应用，这些过程依赖于非湿润表面，这些表面拒绝污垢，具有低附着能，拒绝水(例如，挡风玻璃的涂层)，抗冷凝(例如，在制冷设备中)，或用于气体的孔过滤(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则证明实验。特别是，人们对图案和柱子几何形状对接触线运动动力学的影响以及维持(或阻止)这种运动所需的力知之甚少。拟议的工作将应用新的实验技术来同时定量测量液滴形状和接触线钉扎力，两者都具有单缺陷水平的空间分辨率和快速的时间分辨率。定义形状的孤立缺陷与接触线的相互作用长期以来一直是钉扎理论的主题，被认为是对真实接触线行为描述的理想化。借助高速摄影和灵敏的力传感器，液滴和衬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、碎裂和合并。这些实验可以在当前实验之外的广泛范围内访问和分析速度，并且与应用程序高度相关。拟议的急切的研究方案有以下目标：(I)在一个可以作为界面过程更广泛背景下的缺陷钉扎的实验系统中，寻求对接触线钉扎和去钉扎的准确理解；(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，承诺提供一套改进的工具来分析微观尺度上的接触线运动。这项研究为清洁水、制冷、能源和先进制造等社会需求巨大的领域提供了基本的见解。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。国际和平研究所还将把研究成果纳入现有的课程和演示中。该协会已制定计划，通过积极参加几个校内/校外方案，包括妇女工程学方案、少数族裔工程方案和麦克奈尔学者方案，促进来自代表性不足群体的成员的参与。

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.