Tungsten (W)-doped vanadium dioxide (VO2) particles were successfully synthesized by hydrolysis of vanadyl sulfate mingled with a small amount of sodium tungstate dihydrate and subsequent calcination. XPS analyses demonstrated that the vanadium oxide was composed of stoichiometric VO2, and the doped W content in VO2 particles could be easily controlled by the concentration of W precursor. XRD patterns indicated that all the W-doped VO2 particles were monoclinic crystals, and the W dopant almost had no influence on the crystal structure of VO2 particles. DSC analyses displayed that the critical phase transition temperature of VO2 particles could be reduced to room temperature or even lower by increasing the dopedWfraction. UV-vis-NIR spectra showed that the W-doped VO2 particles embedded acrylic coating had very good thermochromic performance. r 2007 Elsevier B.V. All rights reserved.

BACKGROUND: Polyacrylate/silica nanocomposite latexes have been fabricated using blending methods with silica nanopowder, in situ polymerization with surface-functionalized silica nanoparticles or sol-gel processes with silica precursors. But these approaches have the disadvantages of limited silica load, poor emulsion stability or poor film-forming ability.

The de-agglomeration and dispersion of nano-TiO2 powder is little reported, although nano-TiO2 powder has been widely used due to its unique optical properties. In this study, an agitator bead mill (MiniZETA 03E, Netzsch) accompanied with an ultrasonicator was employed to de-agglomerate the nano-TiO2 powder in butyl acetate, and the effects of ultrasonic pretreatment, dispersant dosage, agitation speed, solid content of TiO2 suspension, and bead diameter were systemically investigated. It is found that ultrasonic pretreatment leads to short grinding time to reach the limiting fineness, low specific energy input, and small limiting mean size. All other technical parameters have also some influence on the limiting fineness and grinding time. However, the former strongly depends on agitation speed while the latter on both agitation speed and dispersant dosage. A solvent-borne nano-TiO2 suspension with limiting mean size of 110 nm can be successfully result under the optimal technical conditions and showed excellent UV-shielding property and transparence when it was incorporated into polyester/melamine coatings.

The Max-Planck-Society is gratefully acknowledged for financial support. S.Z. thanks the Alexander on Humboldt Foundation for a research fellowship. We are also indebted to Dr. Igor Djerdj for recording the HRTEM images and Dr. Minhua Cao and Jinming Wu for carrying out the XRD tests.

Transparent zirconia (ZrO2) nanocrystal dispersions in butyl acetate (BAc) or tetrahydrofuran (THF) were prepared by functionalizing zirconia nanocrystals, synthesized from a solvothermal reaction of zirconium (IV) isopropoxide isopropyl alcohol complex in benzyl alcohol, with 3-methacryloxypropyltrimethoxysilane (MPS), and were embedded into UV-curable polyurethane (PU) coatings. It was found that the ZrO2 concentration was the dominating factor influencing the transparency of the ZrO2 dispersion, while the molar ratio of MPS to ZrO2 was rather efficient in adjusting the amount of MPS attached. Phase separation of the ZrO2 nanocrystals in polyurethane coatings was observed, and was strongly related to the MPS-modified ZrO2 (MPS-ZrO2) content and the amount of MPS chemically bonded. The phase separation of the PU/ZrO2 nanocomposite coatings appeared more seriously for higher MPS-ZrO2 content and higher amounts of MPS attached; thus the transparency of the nanocomposite coatings was lower. However, completely transparent PU/ZrO2 nanocomposite coatings could be still achieved even with a ZrO2 content up to 7.5 wt.-% using a ZrO2/BAc dispersion. Improvements in pendulum hardness, microhardness and scratch resistance of the polyurethane coatings via addition of MPS-ZrO2 were demonstrated, but were not remarkable because of the low cross-linking efficiency of the MPS-ZrO2 nanoparticles resulting from the poor compatibility of the MPS-ZrO2 nanoparticles with the pure PU oligomers.