Mobility\nof Yield Stress Fluids on Lubricant-Impregnated Surfaces

Abstract

A common problem which we encounter\non a daily basis is dispensing of yield stress fluids such as condiments,\nlotions, toothpaste, etc. from containers. Beyond consumer products,\nassuring the flow of yield stress fluids such as crude oil, mud, blood,\npaint, pharmaceutical products, and others, is essential for the respective\nindustries. Elimination of wall-induced friction can lead to significant\nsavings in the energy required for flow of yield stress fluids, as\nwell as associated product loss and cleaning costs. Lubricant-impregnated\nsurfaces (LIS) have been shown to change the dynamic behavior of yield\nstress fluids and enable them to flow without shearing. Despite the\nwide applicability of this technology and its general appeal, the\nfundamental physics governing the flow of yield stress fluids on LIS\nhave not yet been fully explained. In this work, we study the mobility\nof yield stress fluids on LIS, and explain the relationship between\ntheir macroscale flow behavior and the microscale properties of LIS.\nWe show that for yield stress fluids the thermodynamic state of an\nLIS can be the difference between mobility and immobility. We demonstrate\nthat LIS can induce mobility in yield stress fluids even below their\nyield stress allowing them to move as a plug without shearing with\nan infinite slip length. We identify different mobility mechanisms\nand establish a regime map for drag reduction in terms of the shear\nstress to yield stress ratio and the microscopic properties of the\nLIS. We demonstrate these regimes in a practical application of pipe\nflow thereby providing key insights for the design of LIS to induce\nmobility of yield stress fluids in a broad range of practical applications.