Y. Tajitsua, K. Fukudab and T. Takakib
aSmart Structures and Materials Laboratory, Graduate School of Engineering, Kansai University, Suita, Osaka 564-8680, Japan (tajitsu＠ipcku.kansai-u.ac.jp, http://www2.ipcku.kansai-u.ac.jp/~tajitsu/)
bMaterial Science Laboratory, Mitsui Chemicals, Inc., Chiba, Japan
Generally, it is difficult to obtain a polymer film in which the ion transport is stable and dc conductivity is high. At present, polymer film with high conductivity is in great demand. For the realization of such high conductivity, the hydroxyapatite (HAp)-polyvinylalcohol (PVA) nanocomposite film containing Li+ was designed as a solid polymer electrolyte. The HAp-PVA nanocomposite film was prepared according to the following in-situ method. A composite was prepared by reacting Ca(OH) with H3PO4 in the presence of PVA having carboxyl groups. The HAp particles were commonly formed in the shape of spindles (long axis ca. 80 nm and short axis ca. 25 nm). The reactant was stable. Finally, the film was formed by casting method. The film obtained was transparent and flexible. Also, in the film, the HAp particles with nanometer size were uniformly dispersed (HAp-PVA nanocomposite film). Besides, it is possible to draw this HAp-PVA nanocomposite film. The transparent, flexible and drawnable composite film (HAp-PVA nanocomposite film) is very unique as compared with traditional ceramic-polymer composite film (non-nanocomposite film).
The ionic conductivity of the HAp-PVA nanocomposite film with the 35wt% content of LiN(CF3SO2)2 is about 10-4S/m at room temperature. Futhermore, the ionic conductivity of the drawn HAp-PVA nanocomposite film increased. Its value reached to 10-3S/m. These values of ionic conductivity are remarkable. This can be deduced as follows: The HAp-PVA nanocomposite film in which the HAp particles were uniformly dispersed with lithium salt, the Ca2+ ions on the HAp particle surface might interact with the anion site of PVA and counter anion of lithium salt. Such interaction induces the increase of free Li+ and forms the fast transport routes. Consequently, the ionic conductivity of the HAp-PVA nanocomposite film is large.