Mobility of Yield Stress Fluids on Lubricant-Impregnated Surfaces

摘要

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 (US) 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 US have not yet been fully explained. In this work, we study the mobility of yield stress fluids on US, and explain the relationship between their macroscale flow behavior and the microscale properties of US. We show that for yield stress fluids the thermodynamic state of an US can be the difference between mobility and immobility. We demonstrate that US 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 US. We demonstrate these regimes in a practical application of pipe flow thereby providing key insights for the design of US to induce mobility of yield stress fluids in a broad range of practical applications.