Nanoparticle is 60 which means when there are no high

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nanoparticle is 6:0, which means when there are no high surface energy SiO 2 nanoparticles, PFOTES-SiO 2
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 8 nanoparticles self-assembles due to the dense packed –CF 3 groups on their surface which contribute to a relative smoother coating surface with smallest cavities or micro-pores as shown in Fig. 2 and Fig. 1d. The agglomerated nanoparticles in the coating has caused uneven sagging of the TEOS-GLYMO sol during curing when the solvent evaporates, eventually leading to the formation of re-entrant microstructure around the cavities as shown in Fig. 3. Fig. 1 FESEM images of (a) TGS 1:5, (b) TGS 2:4, (c) TGS 3:3, (d) TGS 6:0 coating surfaces. The scale bar is 10 m for all images.
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 9 Fig. 2 Schematic illustration of the cavity formation mechanisms of coatings by in cooperation of different molar ratios of PFOTES-SiO 2 to SiO 2 nanoparticles.
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 10 Fig. 3 FESEM images of (a) TGS 1:5, (b) TGS 2:4, (c) TGS 3:3, (d) TGS 6:0 coating surfaces at a higher magnification. The scale bar is 1 m for all images. It is observed that the micro-pores in TGS 1:5, TGS 2:4, TGS 3:3 and TGS 6:0 coatings exhibit re- entrant structure, Protrusions produced from agglomeration of nanoparticles can be seen on top of the surface and inner wall of the micro-pores. As explained earlier, the size of the re-entrant structure is different due to the ratio of the added hydrophobic and hydrophilic nanoparticles. We show in this work that the size of re-entrant microstructure can be tuned by controlling the molar ratio of PFOTES- SiO 2 to SiO 2 nanoparticles based on the interaction force between PFOTES-SiO 2 and SiO 2 nanoparticles as well as different mobility and dispersibility of the nanoparticles. The re-entrant morphology allows the air beneath the liquid droplet to remain trapped, which enables liquid droplets
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 11 with a range of surface energy to exist in a Cassie-Baxter state [2, 37]. This forms the basis of repellency to water and low surface energy oils. Fig. 4 Coating surface roughness obtained by optical confocal microscope. Fig. 4 shows surface roughness of coatings examined by optical confocal microscope in 700 μm 500 μm surface area. It is noted that by increasing molar of PFOTES-SiO 2 nanoparticles, there is a general trend that the surface roughness of the coatings decreases. The standard deviation in each group is quite large, probably due to the degree of unevenness of the chosen scan locations. Although larger micro-pores are formed in TGS 2:4 coating (Fig.1b) compared to TGS 1:5 coating (Fig.1a), large protrusions in the TGS 1:5 coating surface give rise to the higher surface roughness. The results indicate that agglomeration of nanoparticles was responsible for the surface morphologies such as
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 12 cavities and protrusions which induce surface roughness. Due to difference in surface energy, mobility and dispersibility of PFOTES-SiO 2 and SiO 2
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  • Fall '19
  • Surface tension, nU, Surface energy

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