Preparation And Properties Of Polysiloxane Superhydrophobic Surface

Superhydrophobic surfaces call full attention because they possess ultra large water contact angle and quite small contact angle hysteresis(sliding angle),and show potential application in areas such as self-cleaning, anti-icing, anti-corrosion, drag reduction and water oil separation, and etc. Quite a large number of superhydrophobic surfaces with excellent properties have been obtained at present. However, many efforts are still needed to take the superhydrophobic surfaces into real application:On one hand, many fabrication methods are only suitable for lab research, which are not convenient to produce large area superhydrophobic surfaces. On the other hand, the stabilities of the superhydrophobic surfaces are influenced by the materials made of. For example, carbonic polymers are suffered from the losing of their hydrophobicity outdoors and under high temperature. Therefore, it is very important to choose proper materials, develop reproducible and convenient fabrication methods with large area preparing capability, to get stable superhydrophobic surfaces. Polysiloxanes, profit from their Si-O-Si chains, are good candidates for their good thermal and O3 stability, UV and radiation stability, and weatherability compared with normal polymers. Furthermore, post hydrophobic modification treatment is not necessary when fabricating a polysiloxane superhydrophobic surface, because the existence of hydrophobic groups on polysiloxane. In this dissertation, polysiloxanes are chosen to make stable superhydrophobic surfaces for applications on the basis of disclosing the influences of materials and methods on surface structures, wetting properties and stabilities. Also, simple and effective methods are desirable.To begin with, polypropyl-methylsilsesquioxane (PPMSSQ) superhydrophobic preparing methods are investigated. Films are made by splitting the two slides, between which the sol-gel transition is conducted and a porous structure is made by the spindal decomposition phase separation between the sol skeleton and the solvent. Surface roughness is controlled by the ammonia added and the phase separation thereof. With more ammonia, rougher surface makes the Wenzel to Cassie mode transition, and obtain the superhydrophobicity. However, it is not compatible with conventional coating methods, so the influences of the MTEOS to PTEOS precursor ratio, aging and water adding conditions on the PPMSSQ sol, thin film morphologies, and the wetting properties are investigated in sol dip coating method. It reveals that superhydrophobicity disappears when rough structures at the film surfaces are destroyed by the capillary force introduced by the solvent evaporation employing the fresh sols, or the reduced skeleton-solvent phase separation degree by the extra solvent in aging. Adding water into the aged sols can induce the phase separation between sol skeleton and solvent, lead to aggregation of the skeleton and enlarge the film surface roughness. More PTEOS enhances the phase separation, roughen the surface, and prevent gelling too fast because of its steric hindrance, yet too more PTEOS, which means macro phase separation, makes the sol unstable. When PTEOS: MTEOS=3:7(in volume), the PPMSSQ sol skeletons aggregate effectively, more water, larger aggregation and rougher surfaces. A superhydrophobic surface with contact angle larger than 155°and sliding angle smaller than 10°can be gained under proper water volume condition. Thus we acquired the meaningful PPMSSQ preparing method, that is, the water induced phase separation method.To move on, the thermal stability and failure mechanism of the water induced phase separation superhydrophobic (WIPS-SHS) PPMSSQ film has been studied. The WIPS-SHS PPMSSQ film keeps its superhydrophobicity below 200?,and gradually loses it with temperature increasing above 200?, caused by merging of the nano skeletons and loss of hydrophobic groups, as revealed by SEM,FTIR and TG-DTA.The next chapter of the dissertation focuses on the preparing and researching of the thermal stable superhydrophobic surfaces. Polyphenylsilsesquioxanes (PPSQ) with excellent thermal stability have been synthesized. Combined with the stable phenyl group and the ladder structure confirmed by XRD,29Si CP-MAS NMR and FTIR studies, the PPSQ demonstrates outstanding thermal stability up to 500?in air, compared with other polysiloxanes as DowCorning 840 resin and RTV silicone elastomer. Employing slurry with nano SiO2 particles and PPSQ to prepare SiO2-PPSQ coatings by air spraying, and studying how the SiO2 content will influence the coating surface structures and wetting properties. Then superhydrophobic SiO2-PPSQ coatings are produced. The prepared SiO2-PPSQ coatings possess micro and nano hierarchical structures, and the micro structure is stemmed from the atomized slurry particles (termed as the enforced evaporation effect of spraying) while the nano structure is the consequence of the nanoparticles introducing. A solvent-nonsolvent superhydrophobic PPSQ coating is prepared as well, whose micro structure is the analog of the superhydrophobic SiO2-PPSQ coatings, and nano structure is induced by micro phase separation of PPSQ. The solvent-nonsolvent superhydrophobic PPSQ coating loses its superhydrophobicity above 200?on account of the elimination of nanostructures by the thermal softening of PPSQ, and superhydrophobicity of the SiO2-PPSQ coating retains up to 500?, sustained by the rigidity of the filled SiO2 and excellent thermal stability of PPSQ, which is revealed by FTIR, SEM analysis. It indicates that embedding rigid nanoparticles into the thermal soft structures helps to retain the roughness and keep superhydrophobicity stable.Currently, functionalities of superhydrophobic surfaces are mainly based on the low surface tension and rough structures. Exploration of granting superhydrophobic surfaces functions by embedding functional nanoparticles is conducted. Dispersing effects of the Carbon Black (EC-300) into RTV PDMS are examined; finding out that BYK 9077, butyl acetate and sand milling is benefit for good dispersing. The Ni/CB/PDMS coatings are prepared by spray coating, and researches on the influences of Ni content under given CB loading on surface structures, wetting property and EMI shielding property are conducted. It is found that more Ni can prohibit the atomized paint particles from merging together and make the micro perturbation more distinct on surface, thus transit the three contact line from connected to disconnected, and accomplish the transition from a sticky surface to a roll off surface. Meanwhile, more Ni increases the permeability and enhances the EMI shielding ability of the coating at high frequency. It brings to light that nanoparticles can not only serve as filler to control the surface structures and the wetting property, but also impart superhydrophobic surfaces with functionality to enlarge their application area.