Preparation Of Biomimetic And Hydrophobic Coatings For Marine Engineering And Research On Their Drag-reduction Performance

It is difficult to avoid corrosion and adhesion of marine fouling when marine structures such as ships and platforms work in the marine environment. And Adhesion of marine fouling can not only affect the normal work of structures, increasing maintenance costs on the dock, but also increase the weight and the frictional resistance when a ship sails, resulting in a rising fuel consumption and a waste of resources. Applying some biomimetic and hydrophobic composite coatings is effective in inhibiting corrosion, fouling attachment and improving the drag-reduction property. Therefore, this paper is divided into three parts as follows when the low surface energy and the microscopic roughness are mainly involoved in the preparation of the biomimetic and hydrophobic composite coatings.Firstly, the fluorine-silicone resin(FSR) was choosen as the film-forming composition with a low surface energy, and a micro-rough structure was built with hydroxy carbon nanotubes(CNT-OH) nano-filler, then the biomimetic and hydrophobic CNT-OH/FSR composite coating was prepared with different kinds and amounts of carbon nanotubes. The contact angle, sliding angle and the surface energy of the composite coating were 121°, 21° and 4.28 m N/m respectively. The composite coating has an excellent corrosion resistance and a stable hydrophobicity when its contact angles remained above 95° and the water absorption was 0.59% after the salt immersion test for 25 days. And the coating had excellent physical properties with the pencil hardness and adhesion of 5H and level 0 respectively and it had a good heat stability below 320℃.Secondly, modified silica sol with some hydrophobicity was prepared via a sol-gel method when tetraethoxysilane(TEOS) hydrolyzed and a silane coupling agent hexamethyldisiloxane amine(HMDS) was simultaneously added. Then the modified silica sol, CNT-OH, water and a small amount of an acrylic resin were mixed by using a ball mill, and the composite coating was prepared by a spaying method and a curing treatment. 1H,1H,2H,2H-Perfluorodecyltriethoxysilane(FTES) and HMDS were selected as the surface modifying agent and the biomimetic and hydrophobic CNTOH/ modified silica sol composite coating was prepared. The biomimetic and hydrophobic composite coating has excellent self-cleaning properties with the contact angle and sliding angle of 145°and 15° and the surface energy of 0.595 m N/m. The composite coating has an excellent corrosion resistance and a stable hydrophobicity when its contact angles remained above 122° and the water absorption was 0.37% after the salt immersion test for 25 days. And the coating had excellent physical properties with the pencil hardness and adhesion of 5H and level 0 respectively and it had a good heat stability below 1000℃. The optimum conditions were that the mass ratio of silica sol and hydroxyl carbon nanotubes was 20 with the acrylic acid added in an amount of 30% silica sol. FTES was chosen as a preferable surface modifier when the amount added was 0.8g(in 10 ml ethanol) and the surface modification time was 2h.Thirdly, the drag-reduction properties of the biomimetic and hydrophobic composite coatings were measured by a self-designed flat plate resistance test system with a small scale. Some conclusions were obtained after calibrating the test system. The data obtained with a good repeatability and stability met the test requirements under different equilibrium conditions and weights of the plate. And there was a linear relationship between the force of the test plate and the strain of strain gauges with a slope of 8.9227. Excellent drag-reduction properties were achieved in different biomimetic and hydrophobic composite coatings, when the drag reduction rate of the epoxy resin composite coating from the market purchase, the CNT-OH/FSR composite coating and the CNT-OH/modified silica composite coating were 5.2%, 6.8% and 11.5% respectively compared to the rough plate. The drag-reduction results are attributed to the low surface energy and the microscopic roughness of the biomimetic and hydrophobic composite coatings.