Rapoport Leonid, Solomon Brian R, Varanasi Kripa K
Department of Mechanical Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
ACS Appl Mater Interfaces. 2019 May 1;11(17):16123-16129. doi: 10.1021/acsami.8b21478. Epub 2019 Apr 22.
A common problem which we encounter on a daily basis is dispensing of yield stress fluids such as condiments, lotions, toothpaste, etc. from containers. Beyond consumer products, assuring the flow of yield stress fluids such as crude oil, mud, blood, paint, pharmaceutical products, and others, is essential for the respective industries. Elimination of wall-induced friction can lead to significant savings in the energy required for flow of yield stress fluids, as well as associated product loss and cleaning costs. Lubricant-impregnated surfaces (LIS) have been shown to change the dynamic behavior of yield stress fluids and enable them to flow without shearing. Despite the wide applicability of this technology and its general appeal, the fundamental physics governing the flow of yield stress fluids on LIS have not yet been fully explained. In this work, we study the mobility of yield stress fluids on LIS, and explain the relationship between their macroscale flow behavior and the microscale properties of LIS. We show that for yield stress fluids the thermodynamic state of an LIS can be the difference between mobility and immobility. We demonstrate that LIS can induce mobility in yield stress fluids even below their yield stress allowing them to move as a plug without shearing with an infinite slip length. We identify different mobility mechanisms and establish a regime map for drag reduction in terms of the shear stress to yield stress ratio and the microscopic properties of the LIS. We demonstrate these regimes in a practical application of pipe flow thereby providing key insights for the design of LIS to induce mobility of yield stress fluids in a broad range of practical applications.
我们日常遇到的一个常见问题是从容器中挤出诸如调味品、乳液、牙膏等屈服应力流体。除了消费品之外，确保原油、泥浆、血液、油漆、药品等屈服应力流体的流动对各自行业至关重要。消除壁面诱导摩擦可大幅节省屈服应力流体流动所需的能量，以及相关的产品损失和清洁成本。已证明含润滑剂表面（LIS）会改变屈服应力流体的动态行为，并使其能够在不发生剪切的情况下流动。尽管这项技术具有广泛的适用性和普遍吸引力，但关于屈服应力流体在LIS上流动的基本物理原理尚未得到充分解释。在这项工作中，我们研究了屈服应力流体在LIS上的流动性，并解释了它们的宏观流动行为与LIS微观特性之间的关系。我们表明，对于屈服应力流体，LIS的热力学状态可能是流动性和非流动性的区别所在。我们证明，LIS甚至可以在屈服应力流体低于其屈服应力时诱导其产生流动性，使其能够像柱塞一样移动而不发生剪切，且具有无限的滑移长度。我们确定了不同的流动机制，并根据剪切应力与屈服应力之比以及LIS的微观特性建立了减阻状态图。我们在管道流动的实际应用中展示了这些状态，从而为设计LIS以在广泛的实际应用中诱导屈服应力流体的流动性提供了关键见解。
