| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === Lack of transparency due to the high refractive index of TiO2 and loss of hydrophilicity in the dark are two disadvantages for TiO2 thin films in applications. The main purpose of this work is to resolve these problems. All-nanoparticle thin film coatings by electrostatic layer-by-layer (ELbL) assembly of 7 nm TiO2 and 22 nm SiO2 nanoparticles were performed on glass substrates. Followed by periodic calcination process after every 30 bilayers, multibilayer nanoparticulate thin films (TiO2/SiO2)x and (TiO2/SiO2)x+0.5 with x=1-120 can then be fabricated. Besides the antireflective and self-cleaning properties, the surface wetting sustainability in the dark is another property of the as-fabricated nanoparticulate thin films to be investigated.
Antireflective property was exhibited by all of the nanoparticulate thin films fabricated as revealed by UV-vis transmittance spectra. In addition, average refractive index of 1.25±0.06 was determined by ellipsometer. The results showed that conformal structures of multibilayer with low refractive indices can be successfully fabricated. However, the (TiO2/SiO2)x and (TiO2/SiO2)x+0.5 thin films displayed the different self-cleaning property, which was revealed by the change of the water contact angle on dodecyltrichlorosilane (DDTS)-modified surfaces as a function of time under UV illumination. The photocatalytic degradation rates were found to be strongly dependent on the top-layered material of the nanoparticulate thin films. Furthermore, experimental results showed that TiO2/SiO2 nanoparticulate thin films possess superior natural superhydrophilicity (as represented by static contact angle) as well as surface wetting sustainability (as represented by the variation of contact angle with dark storage time) than those of TiO2 nanoparticulate thin films. Experimental results also revealed that the surface wetting sustainability is enhanced with the increasing of bilayer number. When the bilayer number (x) was less than 30, SiO2 top-layered thin films, (TiO2/SiO2)x, displayed the better surface wetting sustainability than TiO2 top-layered thin films, (TiO2/SiO2)x+0.5. Nevertheless, both (TiO2/SiO2)x and (TiO2/SiO2)x+0.5 thin films showed the outstanding surface wetting sustainability when x was larger than 60. In this case, insignificant influence of top-layered materials on surface wetting sustainability is observed. The “top-layered material effect” and “TiO2/SiO2 interface effect” were then proposed to explain the results mentioned above. When the x was less than 30, the “top-layered material effect” was the dominant factor in surface wetting sustainability due to the slight influence of surface acidity in the less TiO2/SiO2 interface. On the other hand, the “TiO2/SiO2 interface effect” was the dominant factor in surface wetting sustainability due to the enough TiO2/SiO2 interface in the films when the x was larger than 60. The most satisfactory case was found for the nanoparticulate thin films with 120.5 bilayers. Average transmittance higher than 94%, static contact angle on DDTS-modified surface decreased from 125o to 0o under UV (5.5 mW/cm2) illumination in 30 min, and contact angle no exceeded 13o after the dark storage for 7 months can be realized by this nanoparticulate thin film.
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