Fabrication of highly refractive, heat-resistive barium titanate nanocomposite films using a blending route

• Barium titanate nanoparticles used as refractive fillers less photocatalytic than titania.
• Dual surface modification applied to the nanoparticles.
• Blending route to incorporate the modified nanoparticles into heat-resistive polymer.
• Refractive index as high as 1.88 of nanocomposite film using the simple blending route.

Incorporation of the barium titanate (BT) nanoparticles surface modified with coupling agents into a heat-resistive polymer was undertaken to fabricate highly refractive, heat-resistant nanocomposite films. The BT nanoparticles were prepared using the sol–gel method using a 2-methoxyethanol solvent and were dually surface modified with cyanobenzylphosphonate (CPA) and fluoroalkylsilane (FPS). CPA and FPS were employed to provide affinity both for the heat-resistive polymer and for the N-methyl-2-pyrrolidone solvent used to dissolve the polymer, respectively. Mixing the dually surface-modified nanoparticles with the polymer using a blending route enabled the fabrication of nanocomposite films with homogeneous incorporation of the nanoparticles up to a BT content of 65 vol%. Film transparency was scarcely lowered even at the high loadings of the BT nanoparticles, which resulted in the fabrication of nanocomposite films with a refractive index (RI) of 1.86. Hydrothermal treatment was applied to the BT nanoparticles before the dual surface modification to further increase the RI of nanocomposite films. The combination of hydrothermal treatment and dual surface modification applied to the BT nanoparticles resulted in an RI as high as 1.88 for nanocomposite films at a BT content of 60 vol%.

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