| In recent years, surfaces with special wettability have attracted extensive attentionin the research field of material science, physical chemistry and other related fields.People have had a comprehensive understanding of wettability on the surface ofvarious materials in the air, but the underwater wettability is still in a fog. Therefore,how to regulate the underwater wettability of materials needs to be explored.Underwater superoleophobic surfaces typically have an oil contact angleunderwater higher than150°. In recent years, the underwater superoleophobicsurfaces have attracted great research interest due to its promising applications in themanipulation of microfluids, water-oil separation, anti-bioadhesion materials,oil-repellent coatings on ships and other marine equipments and so on.Hydrophilic chemical composition and rough micro-/nanoscale hierarchicalstructure are the two key factors for the construction of underwater superoleophobicsurface. That is to say, hydrophilic materials in air can be applied in preparation ofunderwater superoleophobic surface. Researchers have developed various methods tofabricate underwater superoleophobic surface by imitating the morphology ofbiological surface, but currently most of the methods are very complex. Therefore, it isdifficult to achieve underwater superoleophobic surfaces and make use of them in fact.Chitosan is a kind of biocompatible and biodegradable natural polymer. It is easyto form film and is widely applied in medicine, printing and dyeing industry. At thesame time, chitosan contains hydrophilic groups such as-OH and-NH2; Poly(3,4-ethylenedioxythiophene)(PEDOT) is also a sort of hydrophilic polymer withconductive property. The hydrophilicity makes these materials possible to be used to prepare underwater oleophobic surface.In this dissertation, underwater superoleophobic composite films were preparedon the glass substrates with a simple dip-coating method using hydrophilic SiO2nanoparticles and chitosan; polymer films containing3,4-ethylenedioxythiophene(EDOT) were electrochemically polymerized on indium tin oxide (ITO) glass.Moreover, the factors influencing the wettability of films in the air and underwaterwere investigated. And the application of underwater superoleophobic surface in oildroplet microreactors underwater was explored. The main contents and conclusions areas follows:1. Contact angles of water and1,2-dichloroethane on five kinds of solid surfaces,including pure chitosan film, glass, aluminum, polystyrene (PS) film, andpoly(tetrafluoroethylene)(PTFE) film in the air were measured. Meanwhile,underwater contact angles of1,2–dichloroethane were also detected. It was deductedthat hydrophilic materials in the air can be used for preparation of underwatersuperoleophobic surface in terms of the analysis of the underwater wettability ofmaterials.2. Hydrophilic SiO2nanoparticles and chitosan were used to fabricate underwatersuperoleophobic chitosan-SiO2composite films on the glass substrates with a simpledip-coating method. The surface morphologies were observed by using scanningelectron microscope, surface roughness of films were analyzed with atomic forcemicroscope, and underwater contact angles of1,2-dichloroethane on all kinds of filmswere measured. Factors affecting the surface wettability of composite films, such as theimmersion time in the water, the volume ratio of hydrophilic SiO2-ethanol suspensionto chitosan solution, the chitosan molecular weight and pH values were investigated indetail. When the chitosan-SiO2composite film with the volume ratio of hydrophilicSiO2-ethanol suspension to chitosan (with molecular weight of1million) solution1:1immersed in water for24hours, it showed an underwater oil contact angle (OCA)157.8°and sliding angle (SA)1.9°, exhibiting outstanding underwatersuperoleophobicity. The chitosan-SiO2composite films with molecular weight200,000showed similar underwater wettability. When chitosan-SiO2composite films had arelatively low content of SiO2nanoparticles, pH had great influence on their wettability.That is, the underwater wettability of the films changed in the range of superoleophobicity and oleophobicity, when the pH changed from1to14. However,when the volume ratio of hydrophilic SiO2-ethanol suspension to chitosan solutionwere1:2and3:4, the chitosan-SiO2composite films kept relatively stable underwatersuperoleophobicity as pH altered from1to14. Moreover, the chitosan-SiO2compositefilms were applied to manipulate oil droplets underwater and realized the additionreaction of Br2and styrene in oil droplet microreactors.3. PEDOT underwater superoleophobic surface was electrochemicallypolymerized with3,4-ethylenedioxythiophene. The wettability of copolymer films wasaltered by introducing3-alkylthiophene monomers, including3-ethylthiophene,3-hexylthiophene and3-dodecylthiophene. The influence of molar ratio of EDOT to3-alkylthiophene, the different alkyl side chains in3-alkylthiophene and polymerizationpotential on the wettability of EDOT and3-alkylthiophene copolymer films wereinvestigated. The results showed that pure PEDOT films were superhydrophilic andsuperoleophilic in the air, and superoleophobic underwater; pure poly(3-alkylthiophene) films showed highly hydrophobic and superoleophilic properties inthe air, and were greatly oleophilic underwater. The wettabilities of copolymers in theair and underwater were significantly changed by introducing3-alkylthiophenemonomer, and copolymer films showed highly hydrophobic and oleophilic propertiesin the air, and were oleophilic underwater. The length of alkyl side chains in3-alkylthiophenes and polymerization potential also had influence on the wettability ofcopolymer. The color of PEDOT films treated under different constant potentialschanged from dark to blue, but the surface wettability was similar. |
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