In the absence of any positive liquid pressure

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in the absence of any positive liquid pressure. However, a pressure in reality such as hydrostatic, Laplace or environmental perturbation always exist, which will push the liquids into the cavities [37]. Here, the fabricated re-entrant micro-
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 15 pores can successfully suspend all the tested polar liquids, while partial or complete wetting occurs to non-polar liquids due to the relative pressure. According to the Cassie-Baxter model [38] (1) where is the solid-liquid contact fraction of solid surface wetted by the contacting liquid. For any given equilibrium contact angle , is dominated by in the schematic illustration as shown in Fig. 7 according to Tuteja et al.’s and Liu et al.’s analysis[13, 37]. Since the thickness of the circular contact line is much smaller than and , in our structure larger micro-pore size D resulting in larger ( ), the above term can be simplified as . It is noted that larger micro-pore size D results in larger , which will reduce the value of . As a result, a lower leads to a higher apparent contact angle . TGS 2:4 coating shows largest micro-pore size, therefore, the surface exhibits largest apparent contact angle to all the tested liquids. Fig. 7 Schematic illustration of the cross-section of neighboring re-entrant micro-pores in the coatings which allows for low surface energy liquids. In addition, the size and geometry of micro-pores on TGS 2:4 coating surface is similar to the size of micro-pores in electrodeposited polymer surfaces fabricated by Bellanger et al. [39], the re-entrant
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 16 geometries fabricated by Kim et al. [23] and Lu et al. [40] which all show superomniphobicity. It is noteworthy that contact angles decrease as surface energy of liquid decreases (see Fig. 5). Liquid roll- off angle increases with decrease in liquid surface energy (see Fig. 6). Low surface energy results in a liquid droplet with a low Laplace pressure in air, which has a larger tendency to wet the coating surface with surface tension force pointing downwards. This will lead to increased liquid-solid contact, thus reduced apparent contact angle and increased roll-off angle or even pining effect. Although, non- polar liquids exhibit hydroleophobic contact angle on TGS 2:4 coating, they could not roll-off due to the pining effect. For TGS 1:5, TGS 3:3, TGS 6:0 coating surfaces, wetting occurs for non-polar liquids. Transition from the Cassie–Baxter to the Wenzel state was observed as liquid surface energy decrease. The liquid wetting on GFRE substrate with and without TGS 2:4 coating was demonstrated with water and dodecane as shown in Fig. 8. On bare GFRE substrate, water droplet exhibits contact angle around 80 º (Fig. 8a), and dodecane spreads on the surface with a contact angle of nearly 0 (Fig. 8c). In comparison, a perfectly spherical shape of water droplet can be observed on TGS 2:4 coating surface (Fig. 8b). Even dodecane with low surface energy shows a contact angle larger than 100 (Fig. 8d).
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 17 Fig. 8 Images of water and dodecane droplets gently dropped on GFRE substrates without (a), (c) and
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  • Fall '19
  • Surface tension, nU, Surface energy

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