Keywords superhydrophobic superoleophobic mechanical

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Keywords: superhydrophobic; superoleophobic; mechanical properties; sol-gel; self-cleaning 1. Introduction Natural non-wetting surfaces have gained much attention recently, which has led to the rapid development of mimetic studies for superhydrophobic and superoleophobic surfaces [1-5]. Superhydrophobicity inspired from lotus leaves has been extensively studied using a wide range of materials and fabrication methods over the last two decades. Superoleophobicity was first observed on the skin of marine animals, which are self-cleaning from different types of contaminates. However, the skin of marine animals can only maintain superoleophobicity in water, it becomes superoleophilic in air [4, 6, 7]. Recently, Epstein et al. found that bacterial biofilm exhibits superior repellency against water and lower surface tension liquids in air [8]. Research shows that the skin of springtails enables the formation of stable plastrons upon immersion into water and even into many low-surface-tension liquids such as oil or ethanol [9]. All these studies on superhydrophobic and superoleophobic natural surfaces seem to point out two key factors: appropriate surface features (to trap air) and low surface energy. To create the air-trapping surface structures with low surface energy, a wide range of topologies have been fabricated, including micro mushrooms [10-12], micro hoodoo [13], micro pillar [14-17] and nanopore [15, 18, 19] structures. Research has also been made in generating porous re- entrant surface based on 0D, 1D nanostructures using nanoparticles [20-22], nanotubes [23-25], nanofibers [26], and nanowires [27]. Porous thin films with re-entrant nanostructure derived by spraying of silica nanoparticles bonded with or embedded in polymers, hold good promise as they are simple to prepare, of low cost, and can be easily scaled up for industrial applications. Toward this
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 3 effort, Xiong et al. [28] produced rough particulate coatings which strongly repelled water and diiodomethane using silica particles grafted with two functional polymers. Zhang et al. [29] successfully embedded silica particles in a cross-linked polymer film, and the obtained film exhibited superhydrophobic and superoleophobic. Lee et al. [30] fabricated a coating via spraying silica- fluoropolymer hybrid nanoparticle showing repellency to water and hexadecane. Campos et al. [31] produced a liquid repellent coating by spraying a mixture of fluoroalkylfunctional precipitated silica and a fluoropolymer binder. Hsieh et al. [32] created a water and oil repellent coating combining the colloidal silica spheres with fluorine polymer. The contact angle of six types of liquid with different surface tension (from 25.6 to 72.3 mN/m) on the coating was within the range of 168.3 – 109.7 . The coating also exhibited good adhesion to polypropylene (PP) substrate. Ge et al. [33] prepared superoleophobic and superhydrophobic surface with stringed silica nanoparticles, the surface also showed good resistance to water jetting and sand abrasion tests.
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  • Fall '19
  • Surface tension, nU, Surface energy

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