In-situ preparation of polymer-coated zirconia nanoparticles by decomposition of zirconium-tert-butoxide
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In-situ preparation of polymer-coated zirconia nanoparticles by decomposition of zirconium-tert-butoxide Michael Schallehn, Volker Lorenzen, Johannes Seydel* and Horst Hahn* SusTech GmbH&Co. KG, Petersenstrasse 20, 64287 Darmstadt, Germany *Institute of Materials Science, Darmstadt University of Technology, Petersenstrasse 23, 64287 Darmstadt, Germany Abstract Nanocrystalline zirconia particles coated with polymers have been prepared by a two step Chemical Vapor Synthesis process using a hot wall reactor to synthesize the nanocrystalline ceramic core and a subsequent RF plasma reactor for the polymer coating. The polymer coating is built up of organic byproducts of the pyrolysis of the zirconia precursor. By using continuous and pulsed plasma deposition and variation of the plasma parameters, such as RF power, period and duty-cycle, the structure and thickness of the polymer coating can be influenced. Typical particle radii are in the range of 3 to 4 nm with radii of the ceramic core in the range of 2 nm and a coating thickness in the range of 1 to 2 nm. The powders have been characterized by FTIR, XRD, BET and HRTEM. Consequences for the dispersibility are reported. Introduction Nanocrystalline powders are characterized by a very large surface area (of the order of several hundred m2/g) and surface-to-volume ratio (of the order of 108 / m). Therefore, it can be expected that coatings on these ultrafine particles substantially change their characteristics such as chemical reactivity, or catalytic, optical, magnetic and electronic properties[1]. A special field are polymer coated nanocrystalline ceramic particles. The polymer coating could have the function as a spacer to avoid direct contact of the nanoscaled ceramic particles preventing agglomeration[2]. This can have consequences for the dispersibility of treated and untreated nanoparticles in aequous and organic solvents. Furthermore, this preserves special particle properties even after the fabrication of a bulk material, e.g. superparamagnetism in soft magnets[2]. The use of polymer coated nanocrystalline particles as fillers in polymer nanocomposites could be twofold: 1. due to the lack of scattering of visible light the nanocomposite can be transparent even at high volume fraction of nanoparticles; 2. the improvement of the ceramic-polymer interface could result in better mechanical properties. In this paper the in-situ formation of a polymershell on oxide nanoparticles synthesized by Chemical Vapor Synthesis (CVS) by using a pulsed or continuous plasma is described. The byproducts of the precursor are used for the polymerization. A second route to obtain polymer coatings by using a monomer such as ethene introduced additionally into the plasma reactor will be described in a separate paper[3]. Experimental The powders are prepared by a modular CVS reactor (Fig. 1), which is similar to assemblies described earlier[3, 4]. It is equipped with a second reaction zone (RF plasma reactor), where the polymer coating takes place. With the first reaction zone
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