Fabrication of Nanocomposite Thin Film of Hydroxyapatite and Polyvinylalcohol and its Ionic Conductive Properties
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Fabrication of Nanocomposite Thin Film of Hydroxyapatite and Polyvinylalcohol and its Ionic Conductive Properties Toshihiko Takaki, Kazuyuki Fukuda and Yoshiro Tajitsu 1 Interfacial Science Group, Material Science Laboratory, Mitsui chemicals, Inc., Sodegaura-shi, Chiba, Japan. Smart Structures and Materials laboratory, Graduate School of Engineering, Kansai University, Suita, Osaka 564-8680, Japan. ABSTRACT
A hydroxyapatite (HAp)-polyvinylalcohol (PVA) nanocomposite was prepared by the in-situ method. When the HAp was synthesized by reacting Ca(OH)2 with H3PO4 in the presence of PVA having carboxyl groups, the interaction between the carboxylic groups of PVA and calcium ions of HAp led to the formation of nanometer-sized spindle HAp particles (long axis ca. 80 nm and short axis ca. 25 nm). The reactant was stable and formed transparent thin films by the casting method. Nanometer-sized HAp particles were uniformly dispersed in PVA film. Properties of the HAp-PVA nanocomposite film, such as tensile strength, gas barrier, and pencil hardness, were superior to those of the pure PVA. Furthermore, the nanocomposite film had high ionic conductivity compared to pure PVA and traditional composite. The ionic conductivity of the stretched film (PVA: HAp = 1:1) with 35wt % content of LiN(CF3SO2)2 was about 10-3 S/m at room temperature. Regarding the mechanism of this study, we believe that the HAp particles play a crucial role in increasing the free lithium cations to accelerate the ionic conductivity, according to the ionic interaction on the HAp surface. INTRODUCTION To improve the properties of materials, composites of inorganic materials and polymers have been extensively studied, but the traditional micrometer-scale composite is far too limited to obtain excellent properties. However, nanocomposite materials are potential key materials for application to new optical and electrical devices [1, 2]. The interface between polymer and inorganic particles has different characteristics from bulk material. The size of inorganic particles is decreased to nanometer scale, so the increased surface-to-bulk ratio enhances the unique characteristics. Various methods such as the sol-gel process, modification of particle surface, and clay intercalation technique, are used to prepare nanocomposite of polymer and inorganic particles, depending on the materials [3-5]. However, in all cases, the interaction between inorganic and organic materials is key to the fabrication of nanocomposite materials. Recently, Tanaka et al. reported that the hydroxyapatite (HAp)-collagen nanocomposite was obtained using an excellent in-situ preparation method [6]. The mechanism of formation of HAp-collagen nanocomposite was assumed to be an interaction between surfaces, i.e., Ca2+ ions on the HAp crystals and dissociated carboxyl residues on the collagen molecules. But the nanocomposite of HAp and collagen was only applied to biomaterials such as artificial bone, because the HAp-collagen nanocomposite material has low heat resistance and thin films
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