Transparent and high permittivity films of poly(methyl methacrylate)-grafted 7Â nm barium titanate particles prepared by surface-initiated atom transfer radical polymerization

•PMMA-grafted 7 nm BaTiO3 (BT) particles form transparent and high-dielectric films.•The film with a 10 vol% BT fraction has a dielectric constant of 4.1.•100 mm thickness films have 80% visible light transmittance.

Transparent and high permittivity films were prepared by melt pressing poly(methyl methacrylate) (PMMA)-grafted 7 nm barium titanate (BT) particles. PMMA chains with molecular weights of 32-40 kDa were grafted on BT particle surfaces at a density of 0.2-0.7 chains nm−1 through surface-initiated atom transfer radical polymerization of methyl methacrylate. This yielded BT/PMMA composites with BT volume fractions (φ) ranging from 3.2% to 10%. In melt-pressed BT/PMMA composite films, BT particles were well-dispersed and exhibited high transmittance at 550 nm, with the values standardized for 100 μm thickness being 80%. The relative permittivity of the films at 1 kHz and 25 °C increased to 4.1 upon increasing φ to 10%, according to Lichtenecker's logarithmic mixture formula, while the loss tangent remained as low as 0.04.

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