| Superhydrophobic coatings have shown great application potential in many fields,such as anti-corrosion,self-cleaning,anti-icing and anti-fog,but it is difficult to apply in practice because of the lack of stability.This paper aims to improve the stability of the superhydrophobic coatings.By adding two kinds of nanoparticles Si C and PTFE to the watt plating bath,a kind of Ni-PTFE-Si C superhydrophobic coating was prepared by composite electrodeposition.This method changed the disadvantages of the traditional superhydrophobic coatings which need to be modified by low surface energy materials,and greatly improved the corrosion resistance,wear resistance and durability of the coatings.In this paper,under the guidance of molecular dynamics simulations,the wetting behavior of water droplets on the surface of pure Ni,Si C and PTFE was firstly simulated.Combined with the concentration distribution of water molecules along the Z axis and the adsorption energy between the water droplets and the substrate,it was concluded that the order of hydrophobicity of these three substances was PTFE > Si C > Ni,that is,the embedding of two kinds of nanoparticles was helpful to improve the hydrophobicity of the coating.The effect of coating composition on wettability was further explored.It was found that the adsorption energy between water droplets and coatings decreased at first and then increased with the increase of PTFE content.When the mass ratio of PTFE to Si C reached 7: 3,the adsorption energy was the lowest,that is,the hydrophobicity of the coating was the strongest.Finally,the dispersion effects of different surfactants on Si C nanoparticles were investigated by molecular dynamics simulations.It was found that cationic surfactants CTAB with the opposite charge to Si C nanoparticles adsorbed most rapidly,and achieved excellent dispersion effect through steric hindrance effect and electrostatic repulsion effect.On the basis of molecular dynamics simulations,the preparation process of Ni-PTFE-Si C composite superhydrophobic coating was optimized.The effects of current density,electrodeposition time and the concentration of nanoparticles in the bath on the hydrophobicity of the coating were investigated.Finally,the optimum preparation process was determined as follows: the concentration of PTFE and Si C nanoparticles in the bath was 14 g/L and 6 g/L respectively;the current density of 7 A/dm2 was used for primary electrodeposition for 10 minutes,and then the current density of 15 A/dm2 was used for secondary electrodeposition for5 minutes.The nanoparticles were evenly distributed in the coating and the nickel crystal continued to grow with nanoparticles as the adsorption center,forming a micro-nano dual-scale structure with a maximum contact angle of 156° and a rolling angle close to 0°.The corrosion resistance,wear resistance and durability of the composite coatings were further tested.Electrochemical test results showed that the corrosion resistance efficiency of Ni-PTFE-Si C composite superhydrophobic coatings was as high as 95%.Sanding experiments showed that the composite coatings could still maintain good hydrophobicity after 2 m of wear distance.What’s more,the composite coatings were superhydrophobic after soaking in 3.5%Na Cl solution for five weeks.As a result,Ni-PTFE-Si C composite superhydrophobic coatings had excellent stability.Finally,the inherent mechanism of the good stability of the composite coatings was revealed by molecular dynamics simulation: the modifier and the matrix were adsorbed together by intermolecular force,and the modifier molecular film had large diffusion coefficient,while Si C and PTFE were wrapped by nickel which formed metal bonds with the matrix,and the diffusion coefficient of the composite film was small.So compared with the modified coatings,the composite coatings had better stability. |
