Methyl groups in r sior 3 and perfluoro groups are

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Methyl groups in R 0 -Si(OR) 3 and perfluoro groups are used to form hydrophobic surfaces during drying process due to their very low sueface tension, which will be discussed in Sect. 5 . It is evident that the properties of organic components and ratio of inorganic–organic components have important influences on corrosion resistance of hybrid coatings, and the presence of organic components can increase coating thickness and lower cure temperature. These factors are discussed as follows. 3.1 Properties of organic components Organic components can be introduced into hybrid coat- ings by adding organic molecules or polymers into inor- ganic sols. The polymers mixed with inorganic sols to prepare hybrid coatings have been discussed above. Although weak dispersion forces and van der Waals interactions between organic and inorganic components exit in hybrid coatings, such types of hybrid coatings usually can not provide effective long-term stability during weathering. Strong chemical bonds forming between organic and inorganic components improve anticorrosion of hybrid coatings [ 3 ]. Using 3-(Trimethoxysilyl) propyl methacrylate as a coupling agent in PMMA-SiO 2 hybrid systems increases interaction of organic–inorganic com- ponents [ 19 ]. Different R 0 in R 0 -Si(OR) 3 are introduced into gel net- work to achieve a tailored properties. Epoxy, vinyl, methacrylic, etc. are open to additional polymerization in hybrid coatings, which makes hybrid coatings have a higher cross-linking density and better mechanical prop- erties for anticorrosion. Epoxy group is most used among R 0 in R 0 -Si(OR) 3 for corrosion resistance of metals. Spray-coated, R-Si(OR prime) 3 /TMOS (R = epoxide), thin films are applied on 2024-T3 aluminum alloy at room temperature curing. Nanosized sol particles with epoxy functionalities are formed. Incorporation of a cross-linking agent (primary aliphatic amines) into the coating reduces curing time of the deposited film from [ 7 days to approximately 30 min. Hybrid films cured with amine are hard and highly adherent to the aluminum alloy substrates, exhibiting excellent bare and filiform corrosion resistance, in addition to good compatibility with organic polymer paint systems [ 20 ]. Amino-silanes have the ability to react with epoxy hybrid coatings through both amino- and alkoxy-func- tionalities, which are investigated as cross-linking agents of hybrid coatings instead of diethylenetriamine (DETA). Mono-, di-, and tri-functional amino-silanes used in the study are essentially water-based, and the processing is also environmentally benign. The coatings cross-linked with these amino-silanes offer significant improvement in coating performance over the previously used formulations with DETA and provide better corrosion protection for aluminium alloys in Table 1 [ 31 ].
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