Investigation Of Superhydrophobic Coatings Prepared With Fluorosilane-modified Carbon Nanomaterials And Microcapsules

The demand for superhydrophobic coating has greatly increased,largely because of the enormous industrial application potentials which it possesses.Over the years,many techniques have been employed to fabricate superhydrophobic coatings,but,due to the complexity or costly nature of these techniques,it has prevented them from large industrial scaling.Also,the low interface adhesion and short-term superhydrophobicity has been a huge challenge to the application in the outdoor environment.In view of this,in this work,we proposed three pragmatic approaches of hydrophobic resin polymerization,carbon-based nanofillers modification,and coating preparation to prepare the superhydrophobic coatings,and two-layered composite coating to increase the adhesion.Besides,the fluorosilane microcapsule technique was employed to fabricate multi-stimuli wettability response coatings with self-healing ability to overcome the durability problem associated with superhydrophobicity.Solution polymerization of acrylic monomers and triisopropoxy-vinylsilane was used to synthesis the organic siloxane-acrylic resin.The water contact angle(WCA)of the coating with synthesized resin is 94°.Carbon-based nanofillers including multilayer graphene nanosheets,multi-wall carbon nanotubes(CNTs),and diamond nanoparticles(DNPs)were modified using Heptadecafluoro-1,1,2,2-tetradecyl trimethoxysilane(otherwise known as fluorosilane).The modification process improved the superhydrophobic properties of the carbon-based nanofillers significantly.The WCA of the modified graphene nanosheets is 151° and the sliding angle(SA)is 3°.Also,water droplets could not stay on the surfaces of the CNTs and DNPs;they quickly roll-off on contact with the surfaces.Transmission electron microscope(TEM),Raman spectroscopy,Fourier Transform Infrared Spectroscopy(FTIR),and X-ray photoelectron spectroscopy(XPS)were used to characterize the carbon-based nanofillers in terms of size,shape,chemical,and elemental constituents.Coatings were prepared on the LY12 Aluminum alloy substrate using various mass percentages(5%,10%,15%,and 20%)of the modified graphene nanosheets and the siloxane-acrylic resin.The wettability,anticorrosion,conductive,and accelerated weathering behaviors were comprehensively examined.It is shown that the increasing addition of the modified graphene nanosheets increases the water contact angle and the surface conductivity.At 5 mass%graphene nanosheet loading,the coating is hydrophobic(WCA of 95.8°),and,the coatings-substrate adhesion remains almost unchanged while the electrochemical impedance parameters revealed good anti-corrosion performance up to 10 mass%loading.From 20 mass%loading,the coatings become superhydrophobic with WCA of 152°and SA of 9°.The FTIR results confirmed that the photostabilization ability was improved by the graphene nanosheet loading in the siloxane-acrylic coatings during the accelerated weathering test.Also,the mechanical properties of the coatings were not damaged during the exposure,and pitting corrosion sites were observed only on the 20 mass%graphene filled coatings after 250 hours of exposure.To achieve a good anti-corrosion property with the superhydrophobic graphene coating,a two-layered coating system was adopted.That is,the LY12 aluminum alloy substrate was first coated with the siloxane-acrylic resin without modified graphene nanosheets,thereafter,the sample was sprayed with another coat containing modified graphene nanosheets(25 mass%).The coating offered improved adhesion property.The polarization measurement of the coating showed a positive shift in the corrosion potential signifying an inhibition of the cathodic reaction.Also,it gave a good corrosion protection barrier as further confirmed by the electrochemical impedance parameters.The physical integrity of the coating was not extensively affected including after 120 days of outdoor exposure to snowing,freezing,de-freezing,and surface wetting.These integrated analyses of mechanical,electrochemical properties,and environmental accelerated tests are beneficial to engineering applications of graphene coatings.The superhydrophobic coating(25 mass%graphene loading)showed an excellent self-cleaning ability,that is,good resistance to dirt adhesion.Besides,its superhydrophobic-oleophilic property offered a promising application in oil-water separation.Also,superhydrophobic coatings were prepared using the 40 mass%of modified CNTs and DNPs in the final solid film and the siloxane-acrylic resin,respectively.The superhydrophobic coating with CNTs showed a WCA of 152°and SA of 7°,but the coating adhesion property is very poor resulting in poor corrosion protection ability.On the other hand,the WCA of the superhydrophobic coating with DNPs is 154 0 and the sliding angle is 6°.The electrochemical measurements showed that the coating can offer corrosion protection at the initial period of immersion,but degrades on prolonged exposure.However,the coating revealed a good adhesion by the cross-cut test.In general,the graphene nanosheets proved to be more effective in the design of superhydrophobic coatingsMoreover,urea-formaldehyde(UF)microcapsules filled with fluorosilane were prepared via interfacial polymerization process,and multi-stimuli wettability response coating was fabricated using a mixture of fluorocarbon resin and UF microcapsules Thermogravimetric analysis(TGA),FTIR,and XPS were used to analyze the microcapsules.The synthesized microcapsules have a smooth spherical surface of 700 nm average diameter,and they possess good thermal stability and good resistance to low polar solvent.The microcapsules can be triggered to release their core content on exposure to atmospheric conditions(?25? and-40%relative humidity)resulting in the increase in the water contact angle from 97°to 151°.Two coatings with 16.5 mass%UF microcapsules(16.5PUF)and 23.5 mass%UF microcapsules(23.5PUF)based on the coatings' solid content were prepared using the microcapsules and fluorocarbon resin.The WCA of the 16.5PUF and 23.5PUF is 112°and 151° respectively.The coatings showed good adhesion strength,and also showed an increase in the hydrophobic property after undergoing scratch,solvent compatible and UV accelerated aging test.Also,they offered good self-healing of the hydrophobic property after an initial loss due to alkaline immersion and oxygen plasma etching.The electrochemical measurements revealed an excellent impedance recovery and suppression of corrosion activities,proving them to be a potential candidate material for corrosion protection.