Study On Preparation And Performance Of Sprayable Superhydrophobic Nanocomposite Protective Coatings

Superhydrophobic coatings have great potential in many application fields such as self-cleaning,anti-icing,anti-fouling,drag reduction and anti-corrosion.However,the microstructure of superhydrophobic surface is fragile,which is extremely difficult to recover after physical damages such as friction and extrusion.The loss of superhydrophobic properties limits the practical applications of superhydrophobic surfaces.In addition,most of the preparation methods for superhydrophobic coatings are complex and only feasible for small samples,making it difficult for engineering implementation.Therefore,it is urgent to develop new coating systems and exploit new preparation methods to achieve the simple,large-scale preparation and construction of superhydrophobic coatings.In this thesis,epoxy resin is used as the coating matrix,which is loaded with nano-silica(SiO2),carbon nanotubes(CNT),SiO2-CNT hybrids and corrosion inhibitor containing CNT/layered bimetallic oxide(CNT/LDH/VO3-)nanoparticles,and a facile one-step spraying method is used to prepare superhydrophobic surfaces.A series of sprayable superhydrophobic nanocomposite coatings with excellent wear resistance,chemical stability,corrosion resistance,self-cleaning property and anti-ice/deicing properties are prepared.First,the silane coupling agent KH560 was used to modify SiO2 nanoparticles,and a one-step spraying method was used to prepare composite coatings with different SiO2 particle contents.When the content of modified SiO2 was 30 wt.%,the coating achieved superhydrophobicity,and the water contact angle reached 152.4°.The coating maintained its good superhydrophobic performance within 80 times of tape-peeling tests,exhibiting good mechanical property.The SiO2/epoxy composite coating showed excellent chemical stability in solutions of different pH values.The superhydrophobic structure also made the coating with good anti-icing property.In order to improve the wear resistance of the coating,a CNT/epoxy composite coating was prepared.When the CNT content was 30 wt.%,the coating exhibited the superhydrophobic performance.Because CNTs were entangled and agglomerated in the resin to form micro/nano structures,the coating could maintain the superhydrophobic property after 100 times of tape-peeling tests,showing excellent mechanical durability.The electrochemical impedance spectroscopy(EIS)results showed that the superhydrophobic composite coating with 30 wt.%CNT content possessed excellent corrosion resistance due to the air trapped in the micro-nano structure on the surface,which could effectively isolate the corrosive medium from contacting the coating surface.To further optimize the structure of fillers,SiO2-CNT hybrid particles were prepared by chemical bonding method.When the size of SiO2 particles was 30 nm and the ratio of SiO2 to CNT was 3:1,the composite coating exhibited the optimal superhydrophobicity.Due to the twining and interlocking structure of the SiO2-CNT hybrids,the composite coating could maintain the superhydrophobic property within 300 times of tape-peeling tests and 100 times of rubber frictions,indicating its excellent mechanical durability.The rough structure of the superhydrophobic coating significantly reduced the heat transfer efficiency between the water drops and the coating,and the freezing time of the water drop was 11 times longer than that of the pure epoxy coating.Additionally,thanks to the excellent photothermal conversion performance of CNT,the composite coating could quickly melt the ice layer under light irradiation,achieving the anti-icing and deicing performances.In order to realize the self-healing performance of the superhydrophobic coating,the SiO2-CNT hybrid was added into the shape memory epoxy coating.By adjusting the ratio of the soft segment and the hard segment in the resin system,the shape memory effect of the coating was realized.When the ratio of epoxy resin to curing agent was 1:0.6,the content of flexible segments in the coating was lower,and the glass transition temperature(Tg)reached 40?;when the ratio of epoxy resin to curing agent was 1:1.0,the coating contained more flexible segments,and the Tg was 25?.By heating the two coatings to above Tg or using the electrothermal effect of CNT in the SiO2-CNT hybrid,the shape memory effect of the coating could be triggered,thereby restoring the microstructure,superhydrophobicity and corrosion protection performance of the coating.Finally,CNT/LDH nanoparticles were prepared using the electrostatic adsorption effect of carboxylated CNT and LDH,which were then loaded with NaVO3 corrosion inhibitor.CNT/LDH/VO3-particles were loaded into the coating to prepare a superhydrophobic self-healing coating containing corrosion inhibitors.The loading ratio of corrosion inhibitors in the nanoparticles reached 22.9%.The EIS results showed that the coating containing corrosion inhibitors had the best anti-corrosion performance.This is because when the corrosive media penetrated into the coating,Cl-ions could exchange with the corrosion inhibitors in LDH to accelerate the release of VO3-and promote the formation of a passivation film on the metal surface,thereby improving the protective function of the coating on the metal substrate.