Search

In this work, the silane coupling agents with 4‐carboxyphenyl (PhCOOH), amino, phenyl, 4‐aminophenyl and 4‐phenylmethylketone were employed to modify the interfaces of the polyimide/SiO2 (PIS) nanocomposites, and the effects of the interfacial structures on the dielectric and the mechanical properties for the PI‐based composites were predicted by molecular dynamics simulation. The results showed that the interface structure with PhCOOH simultaneously elevated the static dielectric permittivity (εs) and Young modulus of the PI‐based composites. Due to enhanced intrinsic polarization of the SiO2 particles and the interface polarization in the composites, the εs of PIS‐PhCOOH composites (6.66) was 28% higher than that of PIS (5.21). Young modulus of PIS‐PhCOOH (5.09 GPa) was higher than that of PIS (3.25 GPa), which was attributed to the increase of the number of hydrogen bonds and non‐bond interaction. In addition, the length of PhCOOH was found to be larger than the thickness of excluded volume region, showing that part of PhCOOH could be embedded into the gaps among PI chains and the interfacial load transfer efficiency was reinforced. These results provided an understanding of the atomic‐scale interfacial structures, which was beneficial for the design and preparation of the nanocomposites with superior dielectric and mechanical performances. [ABSTRACT FROM AUTHOR]

A simple and low‐cost approach was proposed to fabricate poly(vinylidene fluoride) (PVDF) and polyimide‐poly(amidic acid) (PI‐PAA) all‐organic hybrid films with excellent dielectric performance by solution casting and thermal imidization process. The results showed that the introduction of PVDF and PAA molecular chains into PI matrix significantly enhanced the dielectric permittivity and energy density of PI‐based composites. The permittivity and energy density of 15 wt% PI‐PAA/PVDF composites were 4.83 at 103 Hz and 5.55 J cm−3, which were 52% and 107% higher than that of PI (3.18 at 103 Hz, 2.68 J cm−3). In addition, the dielectric loss of 15 wt% PI‐PAA/PVDF composites was still maintained at a low level (0.009 at 103 Hz). The molecular dynamics results showed that the polarization strength of composites mainly originated from the intrinsic polarization strength. The intrinsic polarization strength of PI‐PAA/PVDF in the composites was 1010 times higher than interfacial polarization strength, and interfacial polarization was negligible. There was no significant difference between the self‐diffusion coefficients of 15 wt% PI‐PAA/PVDF and PI‐PAA, indicating that the relaxation polarization of polymer molecular chains was suppressed. This work provides an effective way for the preparation of dielectric for all organic high voltage direct current system. [ABSTRACT FROM AUTHOR]

ABSTRACT The morphotropic phase boundary composition 47(Ba0.7Ca0.3)TiO3-0.53Ba(Zr0.2Ti0.8)O3 (calcium barium zirconate titanate, BCZT) were doped in poly(vinylidene fluoride) matrix by solution casting method. The effect of BCZT particles on polarization characteristics of composite films were investigated through dielectric spectra, hysteresis, and thermally stimulated discharge current measurements. It reveals that relative dielectric constant, remnant polarization, and energy storage density gradually increase and reach the maximum value with 39 at 100 Hz, 1.17 μC/cm2, and 3.69 J/cm3 at the concentration of 20 vol % BCZT. The Gaussian method was employed to decompose thermally stimulated discharge current composite peaks and an approximate model was used to analyze the activation energy levels of these films. The results indicated that the introduction of BCZT is effective for the charge carrier traps and activation energy distribution in the relaxation process of composite films. The decreased molecular movements, and increased interfaces formed between the BCZT grains and the poly(vinylidene fluoride) matrix may be responsible for these performances. And a new relaxation peak appeared at about 370 K in composites when BCZT concentration exceeded 20 vol %, which was considered to be caused by the ferroelectric-paraelectric phase transition of BCZT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45362. [ABSTRACT FROM AUTHOR]

Using coupling agent isocyanatopropyltriethoxysilane (ICTOS) to modified nano-TiO2, the polyimide (PI) with different titanium dioxide (TiO2) contents (0, 1, 2, 3, 4, and 5 wt %) doped nano-composites were prepared by sol–gel method (PI/TiO2 ICTOS composites). The effect of ICTOS modification on polarization and time-to-breakdown properties of composites were investigated by thermally stimulated depolarization current (TSDC) method, dielectric, and Corona aging measurements. The TSDC spectra show that ICTOS modification enhanced α-peak intensity and make β-peak disappear in composites. Relevant trap parameters were calculated by an approximate model, and the results indicate that introduction of ICTOS is effective for the charge carrier traps, activation energy distribution in composites. Corona aging measurement show corona resistance was also sufficient improved in PI/TiO2 ICTOS composites. The changes of activation energy and intensity of traps in composites may be responsible for the corona resistance. [ABSTRACT FROM AUTHOR]

This work reports the advanced potassium sodium niobate (K0.5Na0.5NbO3, KNN)/polyimide (KNN/PI) functional hybrid films with 5 vol%, 10 vol%, 20 vol%, 30 vol%, and 40 vol% KNN loaded. The structure, morphology, and dielectric properties of hybrid films have been measured. The results show that the KNN fillers are well dispersed in the PI matrix. An internal boundary layer capacitance structure is formed in the composite films. The dielectric permittivity of the film is as high as 22 when the concentration of KNN filler reaches 40 vol% at 102 Hz, which is five times larger than that of a pure PI matrix. Meanwhile, the loss tangent is lower than 0.05. In addition, the conductivity is lower than 10−8 (S m−1) at 102 Hz, which indicates the excellent insulation and is important for the practical use of this kind of KNN/PI hybrid films. It is believed that the KNN/PI hybrid films could be applied in future electronic fields. POLYM. COMPOS., 35:969-974, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The ceramic thin films of 47(Ba 0.7 Ca 0.3 )TiO 3 –0.53Ba(Zr 0.2 Ti 0.8 )O 3 (BCZT) + x ( x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization ( P r ) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm 2 . Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10 −9 −1.97 × 10 −8 A/cm 2 under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10 −7 A/cm 2 ). [ABSTRACT FROM AUTHOR]