| Inorganic nanoparticles are greatly paid attention in organic coatings field because of their promising applications as the reinforced filler or function filler. Excellent dispersion of nanoparticles without agglomerates or aggregates is essential to exert their roles best, especially for the preparation of transparent organic/inorganic nanocomposite coatings. De-agglomeration and attaching of organic species onto the surfaces of inorganic nanoparticles are usually necessary to improve their dispersion and compatibility with organic media. In this study, commercial TiO2nanopowder and the tungsten-doped vanadium dioxide (VO2(W)) particles made in our lab were de-agglomerated in butyl acetate via a bead-milling process in the presence of3-methacryloxypropyltrimethoxysilane (MPS) and then centrifuged to obtain transparent MPS-TiO2(or VO2(W)) dispersion. These dispersion was further blended with UV-curable organic binder or polysiloxane to prepare nanocomposite films. The detailed research contents and main results are as follows:(1) Titania (TiO2) nanopowder was de-agglomerated in butyl acetate (BAc) via a bead milling process in the presence of MPS, and subsequently centrifuged to obtain the TiO2nanoparticles dispersions with high transparency. The transparent TiO2dispersions were further incorporated into various UV-curable formulations to examine the dispersion behavior of MPS-functionalized TiO2(MPS-TiO2) nanoparticles in UV-curable organic media. Higher molar ratio of MPS/TiO2causes better de-agglomeration of TiO2nanoparticles in BAc, higher amount of MPS attached, and better stabilization of MPS-TiO2nanoparticles, suggesting the excellent compatibility of MPS-TiO2nanoparticles with BAc. However, a critical MPS-TiO2load producing phase separation of MPS-TiO2nanoparticles exists for the dispersion of MPS-TiO2in UV-curable monomers or polyurethane (PU)/monomer mixtures. Higher fraction of PU in organic media leads to lower critical MPS-TiO2load or even serious phase separation at extremely low TiO2content. The lower the amount of the grafted MPS is, the higher the critical MPS-TiO2load is. It implies that MPS-TiO2nanoparticles are partially compatible with UV-curable monomers and incompatible with PU oligomer.(2)Polysiloxane/VO2(W) nanocomposite coatings were successfully prepared by de-agglomerating and modifying the self-made VO2(W) particles with 3-methacryloxypropyltrimethoxysilane (MPS) in butyl acetate, then mixing MPS-functionalized V02(W) nanoparticles with polysiloxane oligomers and subsequently ambient-curing with the aid of3-aminopropyltriethoxysilane. The VO2(W) particles were obtained by hydrolysis of vanadyl sulfate mingled with tungstate dopant and subsequent calcination. The structure and properties of VO2(W) particles and nanocomposite coatings were characterized by XRD, DSC, Vis-NIR spectroscopy, pendulum hardness rocker and nanoindentation instrument. Effects of the synthesis conditions, de-agglomeration process on the properties of VO2(W) particles were investigated. Crystalline VO2(W) particles were gotten only with appropriate amount of air and temperature during calcination step, and, easily reduced to nanometer size by bead-milling. The obtained nanocomposite coatings exhibit good thermochromic performance, ultra-high hardness (～1.0GPa) and high transparency.(3) The stability of the as-synthesized V02(W) nanopowder and its-based film were also investigated. Short-term storage and ultrasonic process have little influence on the crystallinity of the VO2(W). In contrast, bead-milling process is harmful to V02(W) crystals and consequently weaken the NIF modulation ability of the films. Accelerated weathering process can also dramatically weaken the thermochromic performances of the nanocomposite films. Therefore, the service life of VO2(W) nanopowder has to be improved in the future. |
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