Preparation Of Special Wettable Surface And Study On Its Self-Cleaning And Oil-water Separation Performance

Special wettability surfaces have attracted more and more attention and research in the field of self-cleaning and oil-water separation.In addition to water and solid pollutants,the self-cleaning performance of oil pollution is also an important aspect.The self-cleaning and oil dewetting performance of superhydrophilic and underwater superoleophobic surface can only be achieved by wetting in advance or using under water,while the self-cleaning performance after being polluted by oil in air can help us to improve our understanding of self-cleaning process.It’s difficult to realize the complete regeneration in the traditional post-treatment process of the oil absorption material,which is easy to cause secondary pollution.It is of great practical and economic significance to prepare the renewable oil adsorption material that can realize the oil desorption process in a simple way.Superamphiphobic surface is the most ideal self-cleaning material,but its structure and composition requirements are often high,how to design a simple and easy preparation method is an urgent problem.Based on these three consideration,the author prepared three kinds of special wettability surfaces,tested and analyzed their unique self-cleaning and oil-water separation performance.The main work of this thesis are as follows:A simple one-step photoinduced free radical polymerization method was used to prepare a variety of surfaces with different components（including ionic coating,non-ionic hydrophilic coating and non-ionic hydrophobic coating）and structures（smooth and rough）.The differences and causes of self-cleaing and oil dewetting performance when the surface is contaminated with oil in the dry state in air and then put into water were studied,and the unique self-cleaning process and mechanism were also studied.The results show that the wettability of the coating is the most important factor affecting its self-cleaing and oil dewetting performance.The effect of oil dewetting performance of ionic coating surface is relatively better and the anionic coating surface is the best.The water thin film formed by the strong interaction between surface groups and water molecules will cause the oil molecule on the smooth surface to gradually desorb from the surrounding to the center,then change into droplet and finally separate.However,the morphology of the rough surface will form a mechanical barrier,which will makes the oil molecules trapped in and difficult to move.The surface also has excellent anti-fogging,oil-water separation performance and high stability.The rough pH-responsive surface was prepared by self-assembly of nano-SiO₂ particles modified with carboxyl and alkyl groups in a certain proportion on the sand paper substrate by one-step impregnation method.The formation principle and influencing factors of pH-response were studied,and the self-cleaning performance and influencing factors under different conditions were analyzed theoretically.The results show that the key to obtain the best response is the proper composition.Through the process of protonation or deprotonation process,the surface can be conveted from superhydrophobic and superoleophilic in an acid environment to superhydrophilic and underwater superoleophobic in a basic environment with the carboxyl group ratio XCOOH=0.4.The surface in superhydrophilic state can achieve the self-cleaning oil dewetting effect,but different from smooth surface,it presents a segmented "wire drawing" process,which is in the form of contraction-deformation-floatation-fracture process.The reason may be that the oil droplet can form a temporary solid-gas-oil three-phase interface on the surface,while the surface microstructure has a physical restriction on oil molecules during the desorption process,so the effect of oil dewetting process is affected by the surface structure and roughness.This mothod can also achieve the selective oil-water separation performance under two wettability states.By the same impregnation method,the pH-responsive SiO2 nanoparticles were deposited on the 3D adsorption material to prepare the pH-responsive melamine sponge.The chemical composition and surface structure of the sponge were analyzed.The different wettability of the sponge for water droplets with different pH values,oil droplets in solutions with different pH and the reasons for their formation were studied.And the oil-water separation and post-treatment of the sponge were realized after the sponge absorbed oil in the acid solution and then released the oil in the basic solution.The results show that the nanoparticles deposited on the surface of sponge skeleton can form a close packed structure,and improve the surface roughness of the material.The oil absorption of the sponge is directly affected by its different surface wettability.The pH-responsive sponge shows superhydrophobic and superoleophilic state in acid and neutral solution,which can realize the adsorption of oil phase in water.While in basic solution,the sponge will gradually change into superhydrophilic and underwater superoleophobic state,which can release oil slowly and then realize the regeneration of materials.This process is affected by the volume of sponge,and the smaller the volume is,the faster the oil desorption rate is.With the help of vaccum pump,a large volume continuous oil-water separation process and regeneration process can be realized by a simple self-made device.The diatomite particles and nano-SiO2 particles prepared by the Stober method were combined together to form micro-nano composite particles,and then the superamphiphobic particles were obtained through fluorosilane modification.Finally,the superamphiphobic surface was prepared by a simple deposition method.From the perspective of composition and structure,the superamphiphobicity performance is analyzed,and the self-cleaning to various pollutants was realized on this basis.At the same time,the superamphiphobic particles also show some unique physical phenomena.The results show that the huge gaps between the particles can save a large amount of air,and the existence of this air cushion layer is the most important reason for its superamphiphobicity.The superamphiphobic surface has good stability and can maintain the superamphiphobicity under various environments.Due to the anti-wetting properties and the extremely small adhesion force to liquid droplets,the superamphiphobic surface shows excellent self-cleaning performance to water,oil and solid pollutants.Many unique physical phenomena can be observed from the superamphiphobic particles themselves,such as specular reflection,liquid marbles and nanoparticle pad.