Slippery liquid‐infused porous surfaces: The effect of oil on the water repellence of hydrophobic and superhydrophobic soils

Abstract

Soil wettability is important for understanding a wide range of earth system processes, from agricultural productivity to debris flows and sediment fan formation. However, there is limited research considering how soil–water interactions, where the soil grains are naturally hydrophobic, might change in the presence of oil from natural hydrocarbon leakage or oil spills. Here we show how slippery liquid‐infused porous surfaces (SLIPS) apply to hydrophobic soils, by physical modelling of surfaces of different grain sizes and examining their interactions with water before and after impregnation with silicone oil. Using contact and sliding angle measurements and laser scanning fluorescence confocal microscopy, we demonstrate that soil SLIPS can be created with thick oil layers and thin conformal oil layers on median grain sizes of 231 μm and 32 μm, respectively. Until now, SLIPS have only been observed in human‐made materials and biological surfaces. The mechanisms reported here demonstrate that SLIPS can occur in natural granular materials, providing a new mechanism for water‐shedding in soil and sediment systems. Furthermore, the water‐shedding properties may be long lasting as conformal oil layers are stabilized by capillary forces. These results have important implications for understanding soil physics and mechanics where oil is present in a soil, and for agricultural hydrophobicity on shallow slopes. Highlights We model oil contamination on a hydrophobic model soil as a mechanism for creating SLIPS. Soil SLIPS have implications for water‐shedding, oil spill remediation and earth processes. Our model soils exhibit extreme water‐shedding, illustrated by low water droplet sliding angles. This is the first physical modelling observation of SLIPS arising from hydrophobic soil.

The Liquid Young’s Law on SLIPS: Liquid–Liquid Interfacial Tensions and Zisman Plots

“…For any pair of the droplet More details on SLIPS preparation can be found elsewhere. 28,50 For droplets, two series of liquids were used. The first series of liquids was a set of homologous alkanes (purity 99%, Sigma Aldrich) including Pentane (C5H12), Hexane (C6H14), Heptane (C7H16),…”

“…Edible infused-liquids included olive and avocado oils (Sainsbury’s UK) and C8-MCT oil (Wellgard). More details on SLIPS preparation can be found elsewhere. , …”

Evolution of meniscus structures in hydrophobic granular systems

“…binarisation of images, placement of baseline, identification of points along the drop profile) in comparison to the approach used in this work. McCerery et al [50]have used the open source program PyDSA to detect the baseline and the drop profile and fit an ellipse to determine the contact angle. This algorithm, however, uses the reflection of the sessile drop to determine both the placement of the baseline and subsequently the tangent to the drop profile and might therefore not be appropriate for the case where the sessile drop is deposited on a granular, non-reflective surface.…”

Oil sands in glacial till as a driver of fast flow and instability in the former Laurentide Ice Sheet: Alberta, Canada

“…[Color figure can be viewed at wileyonlinelibrary.com] discovered outside of the oil sands region, indicating even more widespread glacial transport. Rutherford (1928) Previous work on the physics of sediment surfaces has shown that oils, such as those found in the AOS, alter the surface chemistry of individual particles-creating a hydrophobic (water repellent) sediment with very limited water infiltration (Gordon et al, 2018;McCerery et al, 2021). The presence of an oil in sediments can also create thin lubricant coatings on the particles that allow for enhanced water shedding, making the sediment 'slippery ' (McCerery et al, 2021).…”

“…Rutherford (1928) Previous work on the physics of sediment surfaces has shown that oils, such as those found in the AOS, alter the surface chemistry of individual particles-creating a hydrophobic (water repellent) sediment with very limited water infiltration (Gordon et al, 2018;McCerery et al, 2021). The presence of an oil in sediments can also create thin lubricant coatings on the particles that allow for enhanced water shedding, making the sediment 'slippery ' (McCerery et al, 2021). For this to occur, several other conditions must be met in the sediment system: (i) the primary sediment must be fine-grained (clay-fine sand sized), (ii) the sediment chemistry must preferentially wet one of the lubricants/ liquids and (iii) sufficient water delivery is required to sustain lubrication.…”