Characterization of Metal-Oxide Nanoparticles: Synthesis and Dispersion in Polymeric Coatings
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Characterization of Metal-Oxide Nanoparticles: Synthesis and Dispersion in Polymeric Coatings Li-Piin Sung, Stephanie Scierka, Mana Baghai-Anaraki, and Derek L. Ho National Institute of Standards and Technology Gaithersburg, MD 20899, U.S.A. ABSTRACT Metal-oxide nanoparticles can be used to optimize UV absorption and to enhance the stiffness, toughness, and probably the service life of polymeric materials. Characterization of the nano- and microstructure dispersion of particles is necessary to optimize the structure-property relationships. Characterizations of both TiO2 particles dispersed in an acrylic-urethane matrix and TiO2 nanostructured films obtained through sol-gel synthesis are discussed. Experimental methods include microscopy (confocal, AFM) and small angle neutron scattering (SANS). Results from SANS experiments, which yield information about the cluster size of the nano-TiO2 particles and the spatial dispersion in various nanoparticle/polymer samples are presented and compared to the results of microscopy studies. INTRODUCTION Metal-oxide particles (or pigments), such as TiO2 and ZnO, serve many functions in the various polymeric materials. Traditionally, they have been used as pigments to enhance the appearance and improve the durability of polymeric products, and usually they have been considered to be inert. As nanosized particles, these materials exhibit broad band UV absorption, a benefit that currently has been exploited only in sunscreen applications. Also, the addition of nanoparticles would likely enhance the stiffness, toughness, and service life of polymeric materials, for example, in applications in which mar resistance is important. Optimizing the material properties of metal-oxide nanoparticle/polymer composites, the microstructure and dispersion (sizes and spatial distribution) of nanoparticles must be characterized as a function of different process conditions. In this project, non-destructive characterization methods, such as small angle neutron scattering (SANS), laser scanning confocal microscopy (LSCM) and atomic force microscopy (AFM), were used to determine the spatial dispersion of nano-pigments (mainly TiO2) in polymeric binders and in nanostructured TiO2 samples prepared using a sol-gel method. For the nanoparticle/polymer composites, particle sizes, dispersion time, and pigment concentration were varied. The results will be compared to these obtained via transmission electron microscopy (TEM). EXPERIMENTAL DETAILS ∗ Materials ∗
Certain instruments or materials are identified in this paper in order to adequately specify experimental details. In no case does it imply endorsement by NIST or imply that it is necessarily the best product for the experimental procedure.
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The particulate materials used in this study included: pigmentary TiO2 (CR-800, Kerr McGee) and nano-TiO2 (P-25, Degussa). The average diameters (provided by manufacturers) of these particles were 190 nm and 25 nm for CR-800 and P-25, respectively. TiO2 particle/polymer films were prepared by disper
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