Background.

Frictional drag causes large energy loss due to shear-induced stress in various fields [1]. Accordingly, various drag reduction (DR) surfaces have been introduced to reduce frictional drag. As a typical DR surface, lubricant-infused surface (LIS) was recently developed by mimicking the insectivorous plant Nepenthes [2]. LIS was fabricated by injecting a lubricant into a porous solid [3]. Thanks to the presence of a slippery lubricating layer, water as well as various organic liquids slide off easily and solid particles do not stick to the LIS surface. However, since the lubricant impregnated in LIS is easily depleted by shear-induced stress, the problem should be resolved to apply LIS to real industrial applications [4].

This study aims to develop a lubricant-inufsed polymer surface (LIPS) for sustainable DR. In contrast to the conventional LIS in which lubricant is impregnated in the voids of solid saffold, LIPS is a slippery surface made by absorbing lubricant oil into polymeric networks of PDMS. In a preliminary study, the proposed LIPS was developed that can effectively replenish the depleted lubricant layer from the internal network of the polymer [5]. The LIPS contains micro-nano particles to hold the replenished lubricant in a sustainable manner. Although the lubricant infused in PDMS surface is inevitably depleted by shear flows, new lubricant will be secreted from the polymer continuously, exhibiting sustainable DR performance (Fig. 1).

Figure 1: Schematic of the sustainable drag reduction of a lubricant-infused polymer surface.

IRES student involvement.

Several LIPS will be fabricated at POSTECH with varying parameters (density, dimension, direction of micro/nano structures). Using a 2D PIV system, an IRES student will measure the flow characteristics of the slip flow at the interface between the fabricated surface and the working fluid for various flow conditions[6]. In addition, the frictional drag exerting on the LIPS surface will be measured in a circulating water channel at POSTECH. The morphological structure of the LIPS will be optimized for achieving sustainable DR.

References

1. Jubran, B., Zurigat, Y., Goosen, M. (2005). "Drag reducing agents in multiphase flow pipelines: Recent trends and future needs", Petroleum Science and Technology 23(11-12): 1403-1424.
2. Bohn, H.F., Federle, W. (2004). "Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface", PNAS 101(39): 14138-14143.
3. Wong, T.S., Kang, S.H., Tang, S.K., Smythe, E.J., Hatton, B.D., Grinthal, A., Aizenberg, J. (2011). "Bioinspired self-repairing slippery surfaces with pressure-stable omni-phobicity", Nature 477(7365): 443-447.
4. Wexler, J. S., Jacobi, I., Stone, H. A. (2015). "Shear-driven failure of liquid-infused surfaces", Physical Review Letters 114(16): 168301.
5. Lee, J., Kim, B., Lee, J., Hong, C. Y., Kim, K., Lee, S. J. (2022). "Bioinspired fatty acid amide-based slippery oleogels for shear-stable lubrication", Advanced Science: e2105528.
6. Kim, H. N., Lee, S. J. (2021). "Shear-driven drainage of lubricant in a spherical cavity of lubricant-infused surface", Physics of Fluids 33(12).