Preparation And Properties Of Bioinspired Drag-Reducing Coating

The tremendous hydrodynamic drag on underwater vehicles and surface ships will not only decrease the velocity and maneuverability of vehicles,but also increase the total maneuverability.Therefore,it is of great significance to reduce the hydrodynamic drag induced by the relative motion of vehicles and liquid efficiently.This thesis learning from nature is bioinspired by the lotus leaves and fish mucus.Various superhydrophobic coatings and hydrogel with drag reduction agent were prepared and used to reduce the hydrodynamic drag,respectively.Chemical deposition method was used to prepare Au superhydrophobic coating on copper foil.The velocity of modified ship model with superhydrophobic coating was higher than the normal ship model.Whereas,the superhydrophobic coating had pool stability and can be broke by slight friction.Therefore,PDMS/Copper superhydrophobic coating combined toughness of resin and roughness of hydrophobic particles exhibiting stability was prepared.The PDMS/Copper superhydrophobic coating can resist mechanical friction,high temperature and hydrostatic pressure.When the submarine model modified with PDMS/Copper superhydrophobic coating was immersed in water,it can be observed that a silvery sheen appears underneath the waterline of the model which defined as plastron effect.According to the sailing experiments of submarine models with and without superhydrophobic coating,the velocity of model with superhydrophobic coating increased by 10-15%,which excluded the view that superhydrophobic coating can decreased the wetted area of moving objects on water leading to the drag reduction,completely.And we insist on that the drag force on the superhydrophobic model is mainly caused by liquid/gas/solid friction,which is less than the liquid/solid friction on the normal model.Superhydrophobic coating with solvent resistance was prepared by a low cost corrosion method in alkaline liquor,and the structure and composition could be controlled by regulating the immersion time in the solution,which ultimately affected the superhydrophobic property of the obtained surface.Compared with the hydrophilic surface,the adhesive force and drag force of the superhydrophobic surface were reduced by nearly 95%and 90%,respectively.A ship model was sanded with abrasive paper and sprayed with an ethanol solution of SiO2 nanoparticles.The cooperative effect of the sanded surface and SiO2 nanoparticles that were modified with silanization resulted in a stable superhydrophobic property.Spray method was applied to prepare superhydrophobic coatings which provided a new avenue for the preparation of drag-reducing coatings.Polymer hydrogel with high mechanical strength was obtained by chemical method.The addition of drag reduction agent increased the mechanical strength of hydrogel and decreased the surface friction coefficient which enhanced the drag reducing effect.The wettability of substrate affected the polymerization which leading to different crosslinking reaction.Hydrophilic substrate can obtained hydrogel with high friction coefficient which will increase the hydrodynamic drag,on the contrary,hydrophobic substrate can procured hydrogel with extremely low friction coefficient which will decrease the hydrodynamic drag.