CAREER: Surfactant impact on laminar drag reduction of realistically-textured superhydrophobic surfaces

减阻涂层已被研究用来降低微流控装置和微冷却应用中可能出现的巨大压差，以及加强化学或生物分析中的控制。超疏水表面是一种很有前途的减阻涂层，它利用微观纹理和疏水性的组合，在浸入液体(如水)中时保留一层薄薄的气泡。然而，自然存在于环境或许多工作液体中的表面活性剂，可以通过对涂层纹理细节高度敏感的机制，大幅降低可实现的减阻效果。本项目将采用模拟、理论和实验相结合的方法来研究具有超疏水表面的层流微通道在表面活性剂存在下的减阻现象。该项目将包括几个教育活动，包括大学课程开发，本科研究计划，当地初中外展活动的动手活动，以及针对下一代科学标准的K-12学习活动。该项目旨在预测表面活性剂在层流中的超疏水减阻，作为织构几何形状、主体流动特性、表面活性剂类型和浓度的函数。这将通过使用数值模拟、理论和实验相结合的方法来研究逐渐增加的复杂性的超疏水表面来实现。数值模拟将能够精确控制表面活性剂的性质和浓度，并求解质量、动量和表面活性剂在流体内部和沿空气-水界面的传输方程。这些结果将被用于开发易于处理的理论模型，这些模型将深入了解流动特性和纹理几何形状如何影响所产生的阻力。理论模型还将用于快速减阻预测。在实验中，超疏水表面将被放置在微流控系统中，并将使用共焦显微镜测量空气-水界面附近的速度场。实验验证了仿真和理论的正确性。这项三管齐下的计算、理论和实验研究将促进我们对现实层流条件下使用超疏水表面的表面活性剂对阻力的影响的理解，并导致可靠的预测和缓解策略。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。

Drag-reducing coatings have been investigated to reduce the large pressure differences that can arise in microfluidic devices and in micro-cooling applications, as well as to enhance control in chemical or biological analysis. Superhydrophobic surfaces is a promising type of drag-reducing coating, which uses a combination of microscopic texture and hydrophobicity to retain a thin coating of air bubbles when submerged in a liquid, like water. However, surfactants, which are naturally present in the environment or in many working liquids, can drastically curtail the achievable drag reduction through a mechanism that is highly sensitive to the details of the coating texture. This project will use simulations, theory, and experiments to investigate drag reduction phenomenon in laminar flow microchannels with superhydrophobic surfaces in the presence of surfactants. The project will encompass several educational activities, including university course developments, an undergraduate research program, a hands-on activity for local junior high school outreach events, and a K-12 learning activity targeting the Next Generation Science Standards.This project aims to predict superhydrophobic drag reduction in laminar flow with surfactants, as a function of texture geometry, bulk flow properties, surfactant type and concentration. This will be achieved by examining superhydrophobic surfaces of progressively increasing complexity, using a combination of numerical simulations, theory, and experiments. The numerical simulations will enable precise control of surfactant properties and concentration and solve the equations for the transport of mass, momentum, and surfactant in the fluid interior and along the air–water interface. The results will be used to develop tractable theoretical models, which will yield insight about how flow properties and texture geometry affect the resulting drag. The theoretical models will also be used for rapid drag reduction predictions. In the experiments, superhydrophobic surfaces will be placed in a microfluidic system, and confocal microscopy will be used to measure velocity fields near the air-water interface. The experiments will validate the simulations and theory. This three-pronged computational, theoretical, and experimental investigation will advance our understanding of surfactant effects on drag using superhydrophobic surfaces in realistic laminar flow conditions and lead to reliable prediction and mitigate strategies.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.