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

1334962 rothstein在本提案中概述的研究中，将开发一种新的超疏水表面设计，该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总体减阻。超疏水表面是通过采用微米或纳米级表面粗糙度的材料并对其进行化学处理使其疏水而设计的。由于这些微尺度和纳米尺度的突出物的疏水性，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值接触，从而形成无剪切的空气-水界面。在本提案中，重点将放在界面形状和变形如何影响减阻，滑移长度以及这些表面用作新型过滤器的潜力。知识优势：在实际应用中实现超疏水表面的挑战之一是空气-水界面不坚固。即使在适度的静态或动态压力下，空气-水界面也会崩溃，使超疏水表面完全湿润，从而消除了预期的减阻效果。本文提出了一种新的微流体设计，可以延长超疏水表面的范围和寿命。这是通过主动背压方案实现的，即使在很大的静压下也能稳定空气-水界面。提出的微流体设计将允许研究界面曲率对减阻、滑移速度和滑移长度的作用。进入被困在超疏水表面的空气将允许在非定常流动条件下探测空气-水界面的稳定性和动力学，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所经历的情况。该设计还将使用不可压缩的油代替空气成为可能，这种油与水不混溶。有了这种注入超疏水表面的液体，可以研究两种液相之间的粘度比对减少阻力的重要性，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开发一系列低孔隙度，高渗透率的微流体过滤器，从一个规则的柱子阵列，其中的柱子是独特的设计，使它们的侧面是超疏水的，并支持无剪切的空气-水界面。将研究后置设计和空气界面形状对过滤器的渗透性及其从流动中去除大小污染物的有效性的影响。更广泛的影响：拟议的研究项目将基础实验润湿现象和流体动力学与商业和工业应用联系起来，减少阻力可以显著降低成本。研究反压超疏水表面的路径，将使它们适用于高压应用，如泵送和商业运输，在这些应用中，大的静压使实施成为一个重大挑战。最后，该提案将开发一种新型的高渗透率、低孔隙度过滤器，可以快速、广泛地应用于商业、生物医学和学术领域。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，我们建议继续并进一步发展一个正在进行的多方面的K-12外展计划。该项目将包括开发流体动力学、表面张力和超疏水性的教学模块、演示文稿和视频，这些内容将通过麻省理工大学STEM项目组织的一系列周末和为期一周的外展活动向初高中教师和学生展示和分发。

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.