Preparation and absorption properties of polystyrene/Ag/TiO 2 multiple coated colloids
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We demonstrated a facile route based on the use of acetone and polyvinylpyrrolidone (PVP) to prepare polystyrene (PS)/Ag/TiO2 multilayered colloids with controllable shell thickness. In this route, PVP absorbed directly onto PS colloid surface, and the Ag seed shell composed of Ag nanoparticles was synthesized directly under the PVP shell by swelling the surface layer of the PS core. Because the PVP shell increased the affinity of the Ag shell to TiO2, the hydrolyzed titania particles could deposit directly onto the core to form the outer TiO2 shell. A seed growth technique and the controllable hydrolysis reaction of tetra-n-butyl titanate were developed to grow the shell thickness of Ag and TiO2, respectively. Studies of the absorption properties indicate that the optical properties of these multilayered composite colloids can be modified by changing the coating species and shell thickness.
I. INTRODUCTION
The fabrication of colloids with properties appropriate for the applications in the fields of electronics,1 optics,2–5 and catalysis6 has been the aim of many recent investigations. The modification of colloids has been found to be a powerful tool for drastically changing and precisely tuning their optical, mechanical, and surface properties. One of the most effective tools for tuning these properties is to coat colloids with different species that possess the desirable properties. Coating latex colloids with metal has been widely investigated due to their applications in surface-enhanced Raman scattering,3,4 photonic crystals,5 catalysis,6 etc. However, the large Van Der Waals forces of the metal shells between composite colloids prevent crystallization at high volume fractions, and the increased levels of ionic strength necessary to counteract these forces will lead to aggregation instead of crystallization. These considerations limit the applications of metallodielectric colloids. Therefore, one solution is to further coat the metal with an additional silica shell.2 The use of a dielectric material as an outer coating material on the metal shell has four advantages. First, the metal shell deposited on the colloids is usually composed of metal nonoparticles1–6 that are easily etched or oxidized in air or aqueous solution; an outer dielectric layer can protect the metal shell from extraneous chemical and physical changes. Second, an outer dielectric layer can reduce the
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Address all correspondence to this author e-mail: [email protected] DOI: 10.1557/JMR.2005.0128 J. Mater. Res., Vol. 20, No. 4, Apr 2005
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interparticle Van Der Waals interactions significantly, allowing for crystallization of the composite colloids to occur.2,5 Third, an outer dielectric layer will prevent the metal shells from touching each other; thereby preventing optical losses in the crystal due to “long-range conduction current.”7 Fourth, the contrast in properties between the metal shell and outer dielectric layer can help produce special or new properties. Finally, the outer di
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