Preperation Of Monodispersed TiO₂ Nano-particles For Electrostatic Seif-assembly Of Thin Film With Structural Colors

Textile coloration is traditionally achieved by means of using chemical colorants such as dyes and pigments. However, the beautiful color from nature is not produced from chemical colorants but from their special physical structures, referred to as structural color, and it results from the interactions of natural light with microstructures with a featured size comparable to visible wavelengths via optical phenomena, such as interference, diffraction or scattering. The typical properties of structural color are high brightness, high saturation, iridescent effect, etc. Compared to the traditional dyeing technology, structural color is an ecological bionic coloring technology of energy saving and emission reduction, and the resultant fabrics obtain a kind of changeable and vivid effect. In this paper, the thin films with structural color through interference effects were prepared from the charged inorganic nanoparticles and polyelectrolyte using electrostatic self-assemble technology. It was believed that this study could provide a reference for textile bionic coloring technology and the development of nano optical technology.The major work could be summarized as follows: 1. The size controlled and monodispersed TiO₂ nanoparticles were prepared by regulating polymerization time, polymerization temperature, molar ratio of isopropyl titanate and water with Sol-Gel method; 2. The self-assembly conditions（e.g. rinsing times, concentration of TiO₂ and PEI） were studied based on the surface properties of substrate, to optimize the suitable self-assembly conditions; 3. Fabrication of TiO₂/PEI thin film and the influence on optical property and structural color of TiO₂/PEI thin film: the mechanism of structural color formation was studied by discussing the effects of TiO₂ nanoparticle size, assembly cycle number and viewing angle on structural color and analyzing the morphology of TiO₂/PEI thin film. Morphology and assembly process of TiO₂/PEI thin film assembled in different cycles: the distribution of TiO₂ nanoparticles in TiO₂/PEI thin film assembled with different cycles was characterized by scanning electron microscopy, and the assembly process of TiO₂/PEI thin film and driving forces during the process were analyzed. 4. Fabrication of SiO₂/TiO₂ film and the influence on optical property and mechanism of structural color: The SiO₂/PEI layer as a low refractive index and TiO₂/PEI as the high refractive index layer to structure high/low refractive index matching（H/L） of the multilayer film. Study their thickness and coordinate number effect on the structural color.The main results were as follows: 1. The particle size of TiO₂ is effectively controlled by changing the molar ratio of isopropyl titanate and water. The TiO₂ particles became mature after polymerization for 12 h at 20℃. 2. Substrate with smooth surface, high electronegativity, hydrophobicity was conducive to the uniform dispersion of TiO₂ particles. The glass surface had a high coverage with uniform dispersion of TiO₂ particles at the condition of 0.5 wt.% PEI, rinsing 3 times and 10 wt.% TiO₂ solution, while the rinse time and concentration of PEI of polyester fabric needed to increase to 4 and 1 wt.%, respectively. 3. The structural color of as-prepared TiO₂/PEI films covered on glass substrate varied with the number of assembly cycle, the size of TiO₂ nanoparticle and viewing angle. The TiO₂/PEI thin film was verified to be a homogeneous porous inorganic/organic composite monolayer with structural color originating from single thin film interference. The growth of TiO₂/PEI thin film was owing to the electrostatic attraction between PEI and TiO₂ nanoparticles, and the distribution of particles was mainly along with the thickness growth direction of the film. The formed TiO₂/PEI thin film was not real LBL（layer- by-layer） film due to the existence of electrostatic attraction and repulsion coexisting system during the assembly process of Ti O2/PEI thin film, and the electrostatic self-assembly process model of TiO₂/PEI thin film was built on basis of this result. 4. The structural color of SiO₂/TiO₂ multilayer varied with the assemble cycles of outer film, and the corresponding wavelength of the structural color has a red shift. It was showed that the SiO₂/TiO₂ multilayer film had lower brightness, the lightness and saturation with changed with increasing assembly cycles, which probably related to the heterogeneous transitional layer in the refractive index of gradual change from n1 to n2.