Development of a sustainable low-friction slippery MIS inspired by mucus layer of marine organisms

Abstract

The maritime industry faces significant challenges due to hydrodynamic friction and biofouling, leading to increased operational costs and environmental impact. To address these issues, slippery surfaces such as superhydrophobic surfaces (SHS) and lubricant-infused surfaces (LIS) have emerged as promising technologies for reducing frictional drag and preventing biofouling. However, these surfaces are prone to degradation due to the depletion of lubricating fluids under shear stress from external flows. Therefore, enhancing the sustainability of these surfaces is crucial for their practical application in industrial environments. In this study, we developed a marine organism-inspired surface (MIS) to overcome the limitations of conventional LIS technology. The biomimetic MIS features spherical cavities filled with liquid lubricant, inspired by the mucus secretion and storage systems of marine organisms, which maintain slippery mucus layers even in harsh seawater conditions. We experimentally demonstrated the drag reduction and anti-biofouling performance of MIS, along with its prolonged sustainability. To optimize MIS performance, we analyzed the dynamic behavior of the impregnated lubricant and the internal flow characteristics of a single cavity system with varying morphological parameters under external shear flow. We found that the radius and opening ratio of the cavities significantly influenced internal flow characteristics, such as recirculation, interfacial deformation, and internal energy dissipation, which in turn affected the drag reduction capability and sustainability of the MIS. Using the Breath Figure (BF) method, we successfully fabricated MIS with lubricant-infused spherical cavities measuring a few microns in diameter. We tested the drag reduction performance of the fabricated MIS in highly turbulent flow conditions, with flow speeds up to 12 m/s, representative of the cruising velocity of a large container ship. Even under such conditions, the nature-inspired surface achieved a frictional drag reduction of up to 39% compared to a bare aluminum surface, outperforming other LIS surfaces reported in previous studies. Additionally, we developed a sprayable version of MIS (sMIS) using a newly proposed sprayable Breath Figure (sBF) method. The primary advantage of sMIS is its ability to coat scalable and curved substrates, which is essential for practical marine applications. The sMIS-coated bluff body model also exhibited significant drag reduction performance in turbulent flow conditions. The successful application of the sBF method to large-area and curved submerged bodies, achieving noticeable drag reduction under high-speed turbulent flows, marks a critical step toward the practical implementation of this technology in the marine industry.