CAREER: Condensation-Driven Phase-Transitioning Surfaces

冷凝在无数的自然和工业活动中发挥着关键作用，如云的形成、电子冷却、发电、乳化液的形成、水的收集和材料的开发。促进表面滴状冷凝(而不是液膜)可在上述许多应用中显著节省能源和成本。近年来，为了促进滴状冷凝，人们对疏水、超疏水和液体注入表面进行了测试。然而，这类表面的性能很容易受到各种削弱机制的影响，例如纹理中的随机液滴成核(导致最终成膜)、高湿度下的表面泛滥、有机污染和表面降解。这个职业项目的目标是了解一类现有材料上的冷凝，这些材料可以由于冷凝本身而发生相变。这种材料具有固体和液体表面的几个有益属性，这些属性可能是克服现有超疏水或液体注入表面所面临的许多挑战的关键。研究这类材料上的冷凝也可以澄清围绕相变的基本原理的长期存在的问题，例如基质导热系数、冷凝速率和相对湿度对液滴生长和热传递速率的作用。这项研究的结果将与教育活动相结合，这些活动旨在通过通过冷凝收集水的本科生(UG)招募学生，并通过大学外联计划(UIC-Chance)与高中(HS)学生接触，寻求增加女性/代表不足的少数族裔学生对工程学的参与。这一职业项目的科学目标是发现新的基础知识，为冷凝应用涂层的开发提供信息，这些涂层基于在冷凝过程中经历相变的表面。这一目标将通过开展全面的研究来实现，以了解在没有/存在凝结的情况下，水滴与相变表面的相互作用，以确定纳米尺度传输现象(例如，液滴下方/周围的温度分布)与由此产生的宏观效应(液滴粘附性降低，高度过冷衬底上的液滴延迟冻结(0oC))之间的关系，作为相变材料性质(如其固态表面结构、水的混和性、热性质)、热力学条件(过冷度和相对湿度)和使用常规(光学/红外显微镜)和AMP的界面性质的函数；先进的诊断工具(环境扫描电子显微镜、X射线相差显微镜)。作为这些研究的一部分，将开发一种新的方法来测量液滴下冷凝表面的温度分布，并以纳米级的空间分辨率进行测量。从实验测量和理论模型建立的相关性将通过数值模拟加以补充，以阐明特殊相变表面上凝结的基本原理。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。

Condensation plays a pivotal role in countless natural and industrial activities, such as in cloud formation, electronic cooling, power generation, emulsion formation, water harvesting, and materials development. Promotion dropwise condensation on surfaces (instead of a liquid film) can result in significant savings in energy and cost in many applications like those mentioned above. In recent years, hydrophobic, superhydrophobic and liquid infused surfaces have been tested to promote dropwise condensation. However, the performance of such surfaces can get compromised easily by a variety of debilitating mechanisms such as random droplet nucleation within textures (leading to eventual film formation), surface flooding at high humidity, organic contamination, and surface degradation. The goal of this CAREER project is to understand condensation on a class of existing materials that can undergo phase-transition due to condensation itself. Such materials possess several beneficial attributes of solid and liquid surfaces that could be the key to overcome many of the challenges faced by the existing superhydrophobic or liquid infused surfaces. Investigation of condensation on such materials could also clarify the long-standing questions on the fundamentals surrounding phase-change, such as the role of substrate thermal conductivity, condensation rate and relative humidity on the growth of droplets and heat-transfer rates. Results from this research will be integrated with educational activities that seek to increase women/underrepresented-minority student participation in engineering via undergraduate (UG) student recruitment for water harvesting via condensation, and engagement with high-school (HS) students through university outreach program (UIC-CHANCE).The scientific objectives of this CAREER project is to discover new fundamental knowledge to inform development of coatings for condensation applications based on surfaces that undergo phase-transitions during condensation. This goal will be accomplished by performing comprehensive studies to understand water droplet interactions with phase-transitioning surfaces in absence/presence of condensation to determine the relation between nanoscale transport phenomena (e.g. temperature distribution below/around droplets) and the resulting macroscopic effects (reduced droplet adhesion, delayed droplet freezing on highly subcooled substrate (0 oC)) as a function of phase-transition material properties (such as their solid-state surface structure, water miscibility, thermal properties), thermodynamic conditions (the degree of subcooling and relative humidity) and interfacial properties using conventional (optical/IR microscopy) & advanced diagnostic tools (Environmental Scanning Electron Microscopy, X-Ray Phase Contrast Microscopy). As part of such investigations, a new methodology will be developed to measure temperature distribution in the condensing surface beneath droplets with nanoscale spatial resolution. The correlations established from experimental measurements and theoretical models will be supplemented with numerical simulations to elucidate the fundamentals of condensation on the special phase-transitioning surfaces.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.