Dual crosslinked PMMA/BaTiO3 polymer nanocomposite dielectrics for flexible film capacitors

Abstract

The BaTiO₃ (BT) nanoparticles were surface modified by polyethylene glycol methacrylate phosphate, and the CC groups on the phosphate were used as the reaction sites with methyl methacrylate (MMA) monomers for in situ polymerization. PMMA-BT polymer nanocomposites were prepared for flexible film capacitor application. The prepared nanocomposites could be dissolved in DMF as colorless and transparent solutions. The surface modification of BT nanoparticles, in situ polymerization, and the thermal crosslinking structure of PMMA-BT were confirmed by FTIR, EDS, XRD, and XPS characterizations. Through high-resolution TEM characterization, the BT nanoparticles were completely coated by organic matter to form the polymer nanocomposite with a core–shell structure. Under the surface and cross-sectional SEM characterization, the polymer nanocomposite films had the advantage of being extremely uniform with a thickness of about 700 nm. The dense and pinhole-free polymer nanocomposite film of PMMA-BT (13 wt%) had a dielectric loss as low as 0.043 and a dielectric constant of 9.55. In terms of the performance, the film capacitor had a maximum energy storage density of 8.5 J m⁻³ and a high dielectric strength of 447 V μm⁻¹. In order to further improve the dielectric properties, PMMA-BT nanocomposites with a double crosslinked network structure were prepared by adding a methylated poly(melamine-co-formaldehyde) solution (PMF) into PMMA-BT. The dielectric loss of the PMMA-BT film after secondary crosslinking was further reduced to 0.031. In addition, the relationship between the dielectric properties and temperature was investigated, and it was found that the polymer nanocomposite films with a double-crosslinked network structure had better thermal stability at high temperatures.