| Superhydrophobicity is defined as water contact angle(WCA)beyond 150°and water sliding angle(WSA)below 10°.Superhydrophobic surfaces have got people's highly attention because of their self-cleaning,water repellence and anti-icing characters etc.Low surface energy and appropriate micro-nano structure are basical factors to prepare superhydrophobic surface.They are also the two key points to make artificial superhydrophobicity nondurable,and restrict the engineering applications.Water impact resistance is a important indicator to evaluate the duarability of superhydrophobicity.Enhancing superhydrophobic surfaces' water impact resistance is valuable in engineering applications.According to mechanism of water hammer pressure and water infiltration on micro strcture,a route that water impact resistance was enhanced by controlling the micro structure of surface was proposed.The micro structure of superhydrophbic surface was changed by CNTs on all organic coatings.Superhydrophobic coatings were prepared and their water impact resistance was analyzed in this paper.Organics include hydrophobic polytetrafluoroethylene(PTFE)particles with high acoustic resistance coefficient,fluorocarbon resin(FEVE)and epoxy resin were adopted to prepare superhydrophobic coatings by spraying and compression molding.The liquid impact resistance of PTFE/FEVE compsite coatings and PTFE/Epoxy composite coatings was studied respectively.CNTs were used to modify these coatings.Firstly,coatings with different content of PTFE particles were prepared by spraying different resin system.There were three steps to evaluate coatings' liquid impact resistance.First step,superhydrophobic coating samples were screened out through analyzing the hydrophobicity of surfaces.Then,water droplet impacting tests were taken on these superhydrophobic coatings to select that which had better performance in liquid impact resistance.Finally,water jet impacting tests were taken for judging the ability of coatings more precisely.Results showed that the hydrophobicity of coatings' surface increases with the content of PTFE particles,and superhydrophobicity was achieved when the content of PTFE particles was more than 60%.For FEVE resin system,the WCA and WSA of coatings were stabilized at 163°-165°and 2°-3°,respectively.For epoxy resin system,they were stabilized at 160°and 3°-4°.The ability of epoxy resin system coatings was better than FEVE's when the recipe was equal;and the spray coatings with 75% PTFE particles had best performance in water jet impacting tests,the coating surfaces could maintain WCA of 160.62°after 22.77 m/s water jet impacting test.Next,the recipes of compression molding coatings were baesd on superhydrophobic spray coatings.There were also two types of coatings prepared with different resins in this study.Results indicated that the WCA and WSA of PTFE/FEVE coatings were about 153°and 9°respectively.PTFE/Epoxy coatings were better with WCA was 159°and WSA was blow 5°.Furthermore,the liquid impact resistance of PTFE/FEVE compression molding coatings was seriously inferior than PTFE/Epoxy coatings'.An obvious example was that the best coating of FEVE resin system(70%PTFE)was wetted after 20 cm height droplet impacting test,but the best PTFE/Epoxy coating(75%PTFE)could maintain the WCA as 149.39°after 26.42 m/s water jet impacting test.Lastly,two typical recipes were chosen in order to research effect of CNTs in this study.Coatings were prepared by both spraying and compression molding with three CNTs propotion respectively.Results revealed that CNTs did not change the hydrophobicity of coatings evidently,but changed the liquid impaleing resistance.The content of PTFE particles of best PTFE/Epoxy coating was 75%,but it changed to 65% in CNTs/PTFE/Epoxy coatings.In conclusion,the coating with best performance in water jet impacting tests is CNTs/PTFE/Epoxy composite coating and the content of PTFE particles and CNTs were 65% and 2%,respectively,which can maintain WCA of 154.73°after 26.42 m/s water jet impacting test.Compared with the results of known literature,commercial superhydrophobicity can maintain WCA of 103.45° after 22.77 m/s water jet impacting test,the water impact resistance of superhydrophobic coatings in this paper excels normal superhydrophobic surfaces' that has reached advanced level in this region. |
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