Nanoparticles surface morphology and roughness of the

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nanoparticles, surface morphology and roughness of the coatings can be tuned by different proportion of PFOTES-SiO 2 and SiO 2 nanoparticles. 3.2 Liquid repellency of the coatings Fig. 5 Liquids contact angles of the coatings, the insets are images of liquid contact angle on TGS 2:4 coating surface. To quantify the repellency of the coatings, static contact angle and roll-off angle of different liquids were measured. Droplet of 4 μL and 10 μL in volume were used for measurement of the static contact angle and roll-off angle separately. As shown in Fig. 5, TGS 2:4 coating surface shows highest repellency to water and polar oils with apparent contact angle larger than 150 ° (The liquid polarity is
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 13 shown in Table 1). The insets in Fig. 5 are liquid apparent contact angles on the TGS 2:4 coating surface. TGS 1:5, TGS 3:3 and TGS 6:0 coating surfaces exhibit apparent contact angle larger than 150 ° to water, glycerol and formamide, and apparent contact angle larger than 130 ° to other polar liquids including diiodomethane, diethanolamine, ethylene glycol, a-bromonaphthalene, castor oil. All polar liquids can roll off easily from these surfaces at various title angles as shown in Fig. 6, which indicates a non-pining state of polar liquids on coating surfaces. The insets in Fig. 6 are video clips of liquid rolling off the TGS 2:4 coating surface (see video of continuous roll-off of liquids in supporting information 1). Fig. 6 Liquids rolling angle of the coatings, the insets are video clips of liquid rolling off the TGS 2:4 coating surface.
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ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 14 Table 1 Liquids with different polarity and surface energy. Chemicals Surface energy (mJ/m 2 ) at 20 °C Polarity Water 72.4 Polar Glycerol 64 Polar Formamide 57.8 Polar Diiodomethane 51.2 Non polar Diethanolamine 48.9 Polar Ethylene glycol 45 Polar a- bromonapthene 43.7 Polar Sunflower oil 35.1 Non polar Castor oil 34.6 Polar Hexadecane 31.8 Non polar Dodecane 29.5 Non polar Although all polar liquids can roll off from TGS 1:5. TGS 2:4, TGS 3:3 and TGS 6:0 coating surface, the roll-off angle is significantly different. Intuitively, TGS 6:0 coating surface with highest molar percentage of the hydrophobic PFOTES-SiO 2 nanoparticles should exhibits lowest roll-off angle, followed by TGS 3:3, TGS 2:4 and TGS 1:5 coatings. However, TGS 2:4 coating surface exhibits much lower roll-off angle than TGS 6:0 coating. It also displays a relative high apparent contact angle which is greater than 100 ° with non-polar liquids, for example dodecane with a surface energy of 29.5 mJ/m 2 . This indicates that besides low surface energy nanoparticles, surface geometry or more specifically the re-entrant structure also plays an important role in superoleophobicity of the coating surface. Fig. 7 schematically illustrated the cross-section of neighboring re-entrant micro-pores in the coatings which allows for low surface energy liquids. When the characteristic length D, the re-entrant structure would suspend a liquid even with
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  • Fall '19
  • Surface tension, nU, Surface energy

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