Single‐Step Wet‐Process Formation of Dual‐Layer Superslippery Coating with Transparency and Robust Omniphobicity

Abstract

repel liquids with low sliding angles, superhydrophobic [4][5][6] and superomniphobic surfaces [7][8][9] have been proposed. Such surfaces are achieved by a controlled nano-to micrometer-scale surface texture with low surface energy. In particular, to achieve superomniphobicity, re-entrant structures with surface fluorination or doubly re-entrant structures are required. [7][8][9] On these surfaces, the droplet−surface contact area is minimized by introducing an air layer between the droplet and the fine-textured surfaces, causing the liquid droplet to roll off the surfaces. [10] This so-called Cassie state is metastable and can collapse under external pressure. Moreover, these surfaces are typically opaque and fragile due to the surface rough structure. [9,11] Notwithstanding the development of functional superhydrophobic/superomniphobic surfaces, the design of these surfaces still requires highly controlled methods, [12] and there is still a limitation in the repellence of low surface energy liquids (e.g., solvents and fluorine agents), mechanical durability, and stability under pressure. [13] Another type of liquid-repellent surface, liquid-infused surfaces (LIS), [13][14][15] repel liquids by introducing a stable lubricant layer (LL) on the solid surface. On LIS, an immiscible liquid droplet slides off because of the lubricity of the surface. A LIS comprises two layers: i) lubricant stabilizing base layer (BL) and ii) LL on top of it. The BL is a nano -to-micrometer porous solid with a high affinity to the lubricant designed by self-assembling nanomaterials, phase separations, templating, crystal growth, and etching processes. [16] The LL comprises a nonvolatile inert liquid, such as silicone oil, fluorinated polymer, fatty acid, or liquid paraffin, [17] and it is formed by simply casting, spreading the lubricant on the BL, and removing the excess by shearing the lubricant or tilting the BL. Further, through appropriate material selection, it is possible to realize optical transparency and a self-repairing function. [13,14] Overall, LIS is promising for achieving a robust omniphobic surface. In particular, the facile preparation of the LIS while maintaining the LIS function is promising. Efforts have been made toward the facile preparation of LIS for practical use. [18,19] However, two-step coating processes are required in most cases to form LIS as it comprises two layers of BL and LL. The twostep coating method requires more processing time and cost Robust coatings that fully repel liquids have a broad range of applications. However, it remains challenging to have an easy, scalable, and substrateindependent preparation method for these coatings. Here, a coating solution that forms stable lubricant surface-to-solid substrates simply by casting, dipping, or spraying without specific limitation in the substrate, is synthesized. Moreover, the coating is formed inside the long narrow tube by flowing the solution. The solution constitutes nanoparticles, a silicone binder, and a binary mixture of a lubricant and a...