Investigation Of Wettability As Well As Friction And Wear Behavior Of Nanosilica Doped Polyvinyl Chloride And Epoxy Resin Composite Films

This thesis summarizes relevant theories about superhydrophobicity. Research progresses ofsuperhydrophobic surfaces in recent years are reviewed, and various methods for preparingsuperhydrophobic surface as well as their advantages and disadvantages are briefed. The effect of doping ofinorganic nanoparticles on the friction and wear behavior of polymer-matrix films is introduced. Moreover,polyvinyl chloride （PVC） porous superhydrophobic film, nanosilica （SiO₂） doped PVC compositesuperhydrophobic film, and SiO₂doped epoxy resin composite film （EP-SiO₂） are prepared by usingdifferent methods. The wetting behavior as well as friction and wear behavior of resultant polymer-matrixfilms has been investigated. The main contents and results are as follows.1. Super-hydrophobic PVC surfaces were prepared on glass slides by combining facile phaseseparation process with solvent/non-solvent coating process, with which no compounds with low surfaceenergy was introduced. After dissolving PVC in tetrahydrofuran and dripping glacial acetic acid to inducephase separation, we obtained superhydrophobic PVC films with controllable microstructures by properlyadjusting the content of the glacial acetic acid and the temperature for volatilization of the solvent. Themorphology of as-prepared superhydrophobic PVC film was observed with a scanning electron microscope（SEM）, and its wetting behavior was examined by measuring water contact angles thereon. Results indicatethat as-prepared superhydrophobic PVC film has porous microstructure with a pore size of10⁵0μm, andPVC matrix has micro/nano hierarchical structure similar to that of lotus leaf. In the meantime, as-preparedPVC film has a water contact angle of151.5°and allows easy water droplet fall off after contact, squeeze,and deformation, showing low adhesion and good superhydrophobicity. Besides, it has similar superhydrophobicity for strong acid and alkaline and retains almost unchanged wetting behavior after beingimmersed in the acid and alkaline, showing good stability. Moreover, non-polar liquids such asdiiodomethane and liquid paraffin can be readily spread over as-prepared PVC film, showing very smallcontact angles. This indicates that as-prepared superhydrophobic PVC film may find promising applicationin storage of oils and in oil-water separation as well.2. PVC-SiO₂composite superhydrophobic films were prepared on glass substrates by combiningorganic-inorganic hybridizing with dual-layer coating. The microstructure of as-prepared PVC-SiO₂composite superhydrophobic films was analyzed using SEM. The wetting behavior of the composite filmswas examined. The effects of PVC content and dosage of nanosilica on water contact angle of thecomposite films were investigated. Moreover, the friction and wear behavior of as-prepared PVC-SiO₂composite superhydrophobic films was evaluated. Results indicate that PVC-SiO₂compositesuperhydrophobic films can be readily prepared by adjusting the dosage of nano-SiO₂. Thesuperhydrophobicity of as-prepared PVC-SiO₂composite films is mainly attributed to the micro/nanohierarchical structure as well as doped nanosilica. Incorporating nano-SiO₂helps to reduce the frictioncoefficient, which is possibly because doped nano-SiO₂leads to increased surface roughness of thecomposite film thereby reducing the actual contact area of the frictional pair. As-prepared PVC-SiO₂PVC-SiO₂composite superhydrophobic films may have potential applications in protection of exteriorwalls of buildings, coating of automobiles, and water-resisting in bath room.3. Epoxy resin with good adhesive capability was used as the polymer matrix to prepare EP-SiO₂composite films possessing good adhesion to glass substrate, where dopant nano-SiO₂（RNS-E） was able tochemically react with the epoxy radical of EP thereby strengthening organic-inorganic interface bonding.The wetting behavior of resultant EP-SiO₂composite films was examined by measuring their water contact angles. A UMT-2multifunctional tribometer was performed to evaluate the friction and wear behavior ofas-prepared EP-SiO₂composite film. Moreover, the friction mechanism of the composite film wasprimarily explored, and the relationship between water contact angles and friction coefficient of thecomposite films was revealed. Results indicate that introducing nano-SiO₂leads to increase of watercontact angle of EP-SiO₂composite films to some extent. However, because nano-SiO₂is hydrophilic,EP-SiO₂composite films do not exhibit superhydrophobicity. In the meantime, incorporation of a properamount of nano-SiO₂contributes to significantly reduce the friction coefficient and increase thecompactness and wear resistance of EP-SiO₂composite films. As-prepared EP-SiO₂composite films, as akind of friction-reducing films, may find application in underwater anti-drag.