Study On Surface Wettability Control Of Several Oxide Films And Polypropylene

Wettability of solid surfaces is an important property taken to consideration in many practical fields. The control of surface wettability has attracted increasing research attention in recent years. This dissertation works mainly on this topic. Firstly, the control of the wettability of several oxide thin films, including TiO2, ZnO, SnO2, Fe2O3 and Cr2O3, is demonstrated by the use of UV irradiation and wet mechanical rubbing. Then, wet chemical treatment has been successfully applied to improve the hydrophilicity of polypropylene surface. In addition, a novel sol-gel approach has been developed for the fabrication of Fe2O3, and Cr2O3 films.Several oxide films, including TiO2, ZnO, SnO2, Fe2O3 and Cr2O3, are fabricated on common glass substrates by sol-gel dip-coating technique. The as-prepared films and corresponding powders are characterized by various techniques, such as DSC, XRD, SEM and AFM . The controllability of their wettability upon UV irradiation and wet mechanical rubbing is investigated. The results indicate that the as-prepared films are dense, uniform and adhered tightly to the substrates. The films are composed of nanocrystalline particles. The irradiation with UV renders the surface of TiO2, ZnO, SnO2 and Fe2O3 hydrophilic. This hydrophilic surface, after wet rubbing treating, can be converted to a relatively hydrophobic one. The hydrophilic-hydrophobic transition is reversible and can be quickly accomplished. The transition from hydrophobicity to hydrophilicity under UV irradiation is believed to be a result of the formation of surface hydroxyl. Also, the transition from hydrophilicity to hydrophobicity under "wet rubbing" may be caused by the elimination of surface hydroxyl on the surface.To improve the hydrophilicity of polypropylene surface, wet chemical treating is used in this study. The following influential factors including the species of oxidizer, concentration of H2SO4, the mass ratio of K2Cr2O4 to H2SO4, treating time, and treating temperature, are investigated. The treating conditions are optimized according to orthogonal tests. After treating, the contact angle decreases by 30%. The FT-IR spectra show an increase of the intensity of the absorption peak of the carboxylic group >C=O at 1714 cm-1. This indicates that the number of polar oxygenous groups increases after treating. At the same time, the microscope images reveal that surface roughness increases after treating. In short,the improvement of surface hydrophilicity is attributed to both the formation of polar oxygenous group and the increase of surface roughness.In addition, in the case of Fe2O3 and Cr2O3 films, a novel approach is developed to synthesize the coating sols. In this approach, inorganic salts, instead of the conventional precursors such as metal alkoxides, are employed as the starting materials. The key to the approach is the use of propylene oxide, which can induce the formation of gels from inorganic salt solutions. The effect of the concentrations of precursor and propylene oxide on the gelation time is investigated, and the suitable conditions have been determined for the preparation of coating sols.