The Role of Interface Shape on Drag Reduction and Filtration using Superhydrophobic Surfaces

1334962 Rothstein在该提案中概述的研究中，将开发一种新的超疏水表面设计，能够在当前超疏水表面无法达到的环境条件下主动控制滑移长度和整体减阻。超疏水表面是通过采用具有微米或纳米级表面粗糙度的材料并对其进行化学处理以使其疏水而设计的。由于这些微米级和纳米级突起的疏水性，当水与超疏水表面接触时，它不会完全润湿表面。相反，它只与表面拓扑结构的峰接触，从而产生无剪切的空气-水界面。在这个建议中，重点将是如何接口的形状和变形影响减阻，滑移长度和潜在的这些表面被用作novel filters.Intellectual优点：超疏水表面在现实世界中的应用实施的挑战之一是，空气-水界面是不稳健的。即使在适度的静态或动态压力下，空气-水界面也会塌陷，完全润湿超疏水表面并消除所需的减阻。在这个提议中，提出了一种新的微流体设计，这将允许延长超疏水表面的范围和寿命。这是通过一个积极的反增压计划，将稳定的空气-水界面，即使在大的静态压力。所提出的微流体设计将允许调查的作用界面曲率的减阻，滑移速度和滑移长度。进入超疏水表面内捕获的空气将允许在不稳定流动条件下探测空气-水界面的稳定性和动力学，所述不稳定流动条件类似于通过施加可变振幅和频率的周期性压力脉冲在湍流中经历的那些。该设计还可以用不可压缩的油代替空气，这种油与水不混溶。通过这种液体注入的超疏水表面，可以研究两个液相之间的粘度比对减阻的重要性，同时在任意压力下保持所需的界面形状，而不需要背压。最后，背压的原理和策略将用于从规则的柱阵列开发一系列低孔隙率，高渗透性的微流体过滤器，其中柱被独特地设计成使得它们的侧面是超疏水的，并且支持无剪切的空气-水界面。后设计和空气界面形状的影响将被研究的过滤器的渗透性和其有效性，在去除大，小的污染物从flow.Broader的影响：拟议的研究计划桥梁基本实验润湿现象和流体动力学与商业和工业应用，减阻可以显着降低成本。对背压超疏水表面的研究路径将使它们能够适应高压应用，如泵送和商业运输，其中大的静压使实施成为一个重大挑战。最后，该提案将开发一类新的高渗透率，低孔隙率过滤器，可以在许多商业，生物医学和学术应用中快速广泛地实施。该项目有几个教育组成部分，包括通过雇用三名REU学生参与研究，他们将与PI和研究生密切合作。此外，我们建议继续和进一步发展正在进行的多方面K-12外展计划。该计划将包括教学模块，演示文稿和视频的开发流体动力学，表面张力和超疏水性，将通过一系列周末和为期一周的推广活动，通过UMASS STEM计划组织，并分发给初中和高中教师和学生。

1334962RothsteinIn the research outlined within this proposal, a new superhydrophobic surface design will be developed that is capable of actively controlling both the slip length and overall drag reduction under environmental conditions inaccessible to current superhydrophobic surfaces. Superhydrophobic surfaces are engineered by taking materials with micron or nanoscale surfaces roughness and chemically treating them to make them hydrophobic. Because of the hydrophobicity of these microscale and nanoscale protrusions, when water is brought in contact with a superhydrophobic surface, it does not fully wet the surface. Instead, it remains in contact with only the peaks of the surface topology resulting in a shear-free air-water interface. In this proposal, the focus will be on how the interface shape and deformation affects drag reduction, slip length and the potential of these surfaces to be used as novel filters.Intellectual Merit :One of the challenges of implementation of superhydrophobic surfaces in real-world applications is that the air-water interface is not robust. Under even modest static or dynamic pressures, the air-water interface can collapse, fully wetting the superhydrophobic surface and eliminating the desired drag reduction. In this proposal, a new microfluidic design is presented that will allow to extend the range and lifetime of superhydrophobic surface. This is achieved through an active back pressurization scheme that will stabilize the air-water interface even under large static pressures. The proposed microfluidic design will allow the investigation of the role of interface curvature on drag reduction, slip velocity and slip length. Access to the air trapped within the superhydrophobic surface will allow the probing of the stability and dynamics of the air water interface under unsteady flow conditions akin to those experienced in turbulent flows through the imposition of a periodic pressure pulse of variable amplitude and frequency. The design will also make it possible to replace the air with incompressible oil that is immiscible in water. With this liquid infused superhydrophobic surfaces the importance of the viscosity ratio between the two liquid phases can be studied on drag reduction while simultaneously maintaining the desired interface shape at arbitrary pressures without the need for back pressurization. Finally, the principles and strategy of back pressurization will be used to develop a series of low-porosity, high-permeability microfluidic filters from a regular array of posts, where the posts are uniquely designed such that their sides are superhydrophobic and support a shear-free air-water interface. The effect of post design and air interface shape will be studied on the permeability of the filter and its effectiveness at removing large and small contaminants from the flow.Broader Impacts:The proposed research program bridges fundamental experimental wetting phenomena and fluid dynamics with commercial and industrial applications where drag reduction could significantly reduce costs. Investigating paths towards back pressurized superhydrophobic surfaces will allow them to be adapted for high-pressure applications such as pumping and commercial shipping where the large static pressures make implementation a significant challenge. Finally, the proposal will develop a new class of high permeability, low porosity filters that can be quickly and broadly implemented in a number of commercial, biomedical and academic applications. The project has several educational components including involvement of undergraduates in the research through the hiring of three REU students who will work closely with the PI and graduate students on the grant. Additionally, we propose the continuation and further development of an ongoing multifaceted K-12 outreach program. This program will include the development of instructional modules, presentations and videos on fluid dynamics, surface tension and superhydrophobicity that will be presented and distributed to both middle and high school teachers and students through a series of weekend and weeklong outreach activities organized through the UMASS STEM program.