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Synthesis of oxide-polymer nanocomposites via plasma polymerization Jens Suffner (1) , Gallus Schechner (2) , Hermann Sieger (1) , Horst Hahn (1),(3) (1) Joint Research Laboratory Nanomaterials (2) SusTech GmbH (3) Institute for Nanotechnology (FZ Karlsruhe) In the last years, nanoscale materials have gained tremendous interest in science due to their unique properties, like superparamagnetism, superplasticity, and quantum confinement. Nanoscale powders are characterized by a large surface-to-volume ratio leading to specific surface areas in the range of several hundreds of square meters per gram. Therefore it is obvious, that the particle-matrix interface has a large impact on the properties of the particles. In this work [1] , the oxide nanoparticles silica and zirconia have been produced by thermal decomposition in a hot wall reactor followed by a subsequent coating with a polymer (see figure 1). Fig. 1: Setup for the in-situ production of polymer coated oxide nanoparticles. Plasma polymerization is a feasible technique for the production of dense coatings on particles. Schallehn et al. [2] have been able to produce plasma polymerized ethylene (ppE) by this technique. Here, we describe the formation of various polymers on silica and zirconia and study the influence of the monomer on the resulting surface properties. A large variety of substances can be used as starting material for the organic coating, what allows tailoring of the interface properties and adopting the surface properties to the matrix medium by the right choice of monomer, e.g. siloxanes for silicone matrices. The following monomers could be successfully coated on the oxide core: • Hexafluoro-m-xylene (C8H4F6) and hexafluoropropene (C3F6), leading to highly fluorinated surfaces • Octamethylcyclotetrasiloxane (C8H24S4O4), leading to a siloxane surface • Methylmethacrylate (MMA, C5H8O2) and ethyl-2-cyanoacrylate (ECA, C6H7O2N), leading to an acrylate surface - 108 -
Figure 2 shows the successful coating of plasma polymerized hexafluoro-m-xylene on ZrO2. Polymerization through plasma agitation always leads to an amorphous coating that can be clearly distinguished from the dark and crystalline oxide core. In all cases, oxide particles can be produced with diameters smaller than 10 nm and varying coating thickness of 2 - 10 nm. Fig. 2: Transmission electron micrograph of an amorphous polymer coating on the zirconia core (Image by R. Schierholz, Structural research division). Transmittance T [a.u.] 3180 ν (N-H) ν (C-H) ppECA/ SiO (p) 2 CO 2 ppMMA/ SiO 2 SiO 2 1600 ν 1710 (C=C) ν (-C=O) δ (C-H) 880 δ (Si(CH 3 ) 2 ) 3000 2000 1000 Wavenumber [cm -1 ] * * * * SiO 2 * * * 664 δ (N-H 2 ) Fig. 3: FT-IR spectra of uncoated silica, silica coated with plasma polymerized MMA (ppMMA/SiO2) and silica coated with plasma polymerized ECA (ppECA/SiO2). The influence of the coating material on the dispersability was studied in the case of the acrylate-based coatings ppMMA and ppECA on silica [3] . Powders derived from methylmethacrylate are characterised by a hydrophobic surface, making it impossible to disperse them in water. The powders are not wettable. The exchange of a methyl group to a cyano group (-CN) in the monomer leads to enhanced dispersability in water. In the plasma, the C≡N bond is split and reassembled with hydrogen in the coating to form –NH2 groups, as determined by FT-IR spectroscopy (Fig. 3). The hydrocarbon bands of the coating can be found in the range of 2875 – 2960 cm -1 . Vibrations of the methacrylate can be identified around 1710 cm -1 for the C=O bond and around 1600 cm -1 for the double bonded carbon. The vibrations responsible for δ(N-H2) around 664 cm -1 and for ν(N-H) around 3180 cm -1 appear only in the spectrum measured on particles coated with ECA-derived coatings. Literatur: [1] J. Suffner, Diploma thesis, Faculty of Materials- and Geo-Sciences (TU Darmstadt), 2006 [2] M. Schallehn, M. Winterer, T.E. Weidrich, U. Keiderling, H. Hahn, Chem. Vap. Deposition 2001, 9, 40. [3] J. Suffner, G. Schechner, H. Sieger, H. Hahn, Chem. Vap. Deposition (accepted for publication) - 109 - * * *
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