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In this paper, the anti-aging properties of composites doped with nano and micro BiFeO3 and treated with different magnetic fields were studied by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy. SEM results showed that thermal aging had a significant effect on LDPE and composites, and the effect of magnetization treatment on the structure was significantly weakened. FTIR results showed that with the increase in aging time, the carbonyl content increased, the carbonyl content of nanocomposites increased less, and the carbonyl content of micron composites increased gently. DSC results showed that the addition of BiFeO3 acted as heterogeneous nucleation agent, and the orientation of magnetic field changed the arrangement of molecular chain and improved the crystallinity of the composite. Compared with the aged LDPE, the aged composite had lower dielectric constant and loss factor. 0.2 wt% nano and micro BiFeO3/LDPE composites had significant anti-aging ability, and the dielectric constant and loss factor of the composites could be further reduced by magnetic field treatment. All the test results showed that the doping of BiFeO3 and magnetic field treatment could change the internal structure of the composite, increase the compactness of the material, and make the composite have obvious thermal aging resistance. [ABSTRACT FROM AUTHOR]

Using melt mixing, we produced a ceramic/polymer composite with a matrix of polyvinylidene fluoride (PVDF) and a filler of 5 vol.% Ni-deposited CaCu3Ti4O12 core-shell ceramic particles (CCTO@Ni), and studied its prominent dielectric characteristics for the first. Its phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, respectively. After treating the composite films with various durations of a magnetic field treatment, we compared their dielectric properties. We found that the CCTO@Ni ceramic had a typical urchin-like core-shell structure, and that different durations of the magnetic field treatment produced different distributions of ceramic particles in the PVDF matrix. The dielectric permittivity of the untreated CCTO@Ni/PVDF composite was 20% higher than that of neat PVDF, and it had a low loss tangent. However, only the composite treated for 30 min in the magnetic field had an ultra-high dielectric permittivity of 1.41 × 104 at 10 Hz, three orders of magnitude higher than the untreated composite, which declined dramatically with increasing frequency, accompanied by an insulating-conducting phase transition and an increase in loss tangent. Our results demonstrate that changes in the dielectric properties of PVDF composites with magnetic field treatment are closely related to the percolation effect and interfacial polarization. [ABSTRACT FROM AUTHOR]

We report a novel low-density polyethylene (LDPE) composite filled with nickelcoated CaCu3Ti4O12 ceramic (denoted as CCTO@Ni), prepared by a melt mixing technique, and its prominent dielectric characteristics. The effects of magnetic field treatment on the dielectric properties of CCTO@Ni/LDPE composite films with a low filler concentration of 10 vol.% were investigated. Our results show that the dielectric permittivity, loss tangent, and conductivity of the LDPE composite films initially improved and then decreased with increasing treatment time under the applied magnetic field. Magnetic field treatment for 60 min led to an ultrahigh dielectric permittivity value of 1.57 × 104, four orders of magnitude higher than that of the pure LDPE material. Our results indicate that the magnetic treatment may have induced a percolation effect and enhanced the interfacial polarization of the CCTO@Ni/LDPE composite, resulting in the observed changes in its dielectric properties. [ABSTRACT FROM AUTHOR]

The effects of nanoparticles with different shapes on the interface bond energy in a polyimide/KTa0·5Nb0·5O3 composite were investigated using molecular dynamic simulations. The simulation results showed that the bond energy of sphere particles were 20-85 kcal mol−1, whereas the bond energies of three shape nanoparticles surface atoms (cube, cylinder and cone) were 5-30 kcal mol−1. This indicated that Van der Waals force and hydrogen bonds existed between the matrix and the fillers. The bond strengths of the small nanoparticles were more than the larger nanoparticles due to the size effect. At the same doping volume fraction, the bond energy of the sphere nanoclusters was significantly larger than the ones of other shaped nanoparticles. The introduction of sphere nanoparticles and the small-sized nanoparticles has the potential to be an effective way to improve the properties of the polyimide/KTa0·5Nb0·5O3 composites. [ABSTRACT FROM AUTHOR]