Preparation And Properties Of Super-Hydrophobic Doped Fluorinated Polymer/Silica Sol Composite Coatings

With the constant development of science and technology, the requirement for material properties becomes higher and higher. Scientists give more attention to super-hydrophobic surface during recent years, it is now playing a more and more importance role in surface science for it's attracted potential industry applications. Conventionally, super-hydrophobic surface has been produced mainly in two ways. One is to create a rough structure on a hydrophobic surface, and the other is to modify a rough surface by materials with low surface free energy. Unfortunately, it rather difficult to prepare this kind of material by applied process due to the limitation of their own characteristics. Simple process conditions for preparation super-hydrophobic materials with good mechanical properties are a difficulty in this field.In this paper, the fluorinater acrylate polymer with hydrophobic groups -CF₃, -CH₃ and -CH₂ has been synthesized by radical copolymerization, the hydrophobic coating with water contact angle 102^? was prepared by crosslinking with HMMM. The well-proportioned composite sols were prepared by using simple sol-gel technology with tetraethyl orthosilicate (TEOS) and methyl triethoxy silane (MTES) as the precursors in alcohol-soluble fluorinated polymer solution with PTFE doping under the hydrochloric acid and deficiency of water conditions. alkoxides were partly hydrolyzed, the condensation process was suppressed due to the deficient amount of water available in the system and in hydrochloric acid medium, this deficiency of water prevented phase segregation that has a tendency to occur due to the organic polymer introduced into the systems. After the surface of material was coated by composite sol, the composite coating was formed on substrate surface through the surface gelation treatment technology, the gelation occurred only on the composite coating surface, and condensation polymerizing - cross at high temperature. The close-grained coating with microstructure surface was prepared.Physical techniques including FTIR, DSC, XRD, SEM, TEM, XPS and JC2000A were applied to investigate the characteristic of the hybrid materials, results of the surface gelation treatment and hydrophobicity of the composite coatings. The hydrophobic models in the surfaces of the coatings were discussed, the mechanical properties and water proof performance of the composite coatings were measured. The results are as bellow:1. The PTFE doping fluoropolymer/silica sol composite coating is considerable different between the chemical compositions from surface to the interior of the coating, the gelation only on the surface of the composite coating, the collapse of the gel network is avoided during drying. 2. The silica dioxide particles were obtained after the composite coating was surface gelation treated in the surface of coating. The sizes of the silica dioxide particles were decreased with the increase of pH values and the rising of treatment times. The agglomerates were consisting of amorphous silica dioxide particles and crystalline PTFE particles.3. The angles for the composite coating were 155°and 9°for water contact angle and water sliding angle repectively, the composite coating prepared by this means was super-hydrophobic. SEM and AFM results indicated that there existed micro- and nanoscale hierarchical structures on the surface of the coating, it is very similar to the structure of the surface of a lotus leaf. The drop height of agglomerates was estimated at 1μm, the interval between two agglomerates was estimated at 6.5μm, the size of silica dioxide particle was estimated at 300 nm. The microstructure could only formed to the place of 5μm under surface, and tightness and continuity inside the coating.4. The results of the experiment reveal that adhesion, flexility and rigidity of the composite coating were as good as that of the fluorinated acrylate copolymer coating, although the impact intensity of composite coating was decreased consistent with the requirements of ship, bridge and steel structure and so on. The results of electrochemical impedance spectroscopy showed the composite coating has much stronger resistance ability to corrosive medium permeation of the coating, comparing with the fluorinated acrylate copolymer coating.5. In order to reveal the hydrophobic nature of the cross-linked fluorinated acrylate copolymer smooth coating theoretically, the equal probabilistic distribution model was set up, The results were in good agreement with experiments.6. The wetting behavior of the composite coating surface exhibited Wenzel model when the surface's roughness was lower enough, and Cassie model was available at higher enough. It was assumed that the hierarchical structures of the composite coating were agree with the fractal structures described by Koch curve. Based on the fractal structure equation, the super-hydrophobic fractal structure model of the composite coating was constructed, the model agrees with the experimental data well.