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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]

The functional groups on the surface of nanofillers could significantly improve the organic-inorganic interfacial compatibility and the interfacial load transfer efficiency. Wenlong Yang and Yu Wang designed the cover image that showed the interface structure of the polyimide/silica composites. [Extracted from the article]

Wenlong Yang and Yu Wang designed the cover image that shows flexible all-organic polyimide-poly(amidic acid)/poly(vinylidene fluoride) hybrid films. The incorporation of polyvinylidene fluoride and poly(amidic acid) with high intrinsic polarization strength into polyimide could significantly enhance the energy density and suppress the dielectric loss of PI-based composites. [Extracted from the article]

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]

ABSTRACT Hybrid polyimide (PI)/titanium dioxide (TiO2) films were prepared by in situ polymerization and sol-gel and in-sol methods (where in-sol method indicates that in situ polymerization and the sol-gel method were used in the same samples). The mechanical and electrical properties were found to be sensitive to the processing methods and the dispersion of nano titanium dioxide (nano-TiO2) in the PI matrix. For the PI/TiO2 films prepared by the in situ polymerization method, their tensile strength increased with increasing TiO2- in situ ('TiO2- in situ' is 'the TiO2 nano-particles prepared by in situ polymerization method') concentration. However, the optimal corona lifetime of the PI/TiO2 films was 15 min at 20 kHz and 2 kV because of poor dispersion. For the PI/TiO2 films prepared by the sol-gel method, the corona lifetime reached 113 min because of superior dispersion and a tensile strength of about 19.63 MPa. A balance of mechanical and electrical performances was achieved with the in-sol method. The corona-resistant life of the PI/TiO2 films was 43 min, which was about six times longer than that of the neat PI. Their tensile strength was 83.5 MPa; these films showed no decrease in this value compared with the pure PI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44666. [ABSTRACT FROM AUTHOR]

ABSTRACT Polyimide (PI) films filled with K0.5Na0.5NbO3 (KNN50) particles at different weight 0, 5, 10, and 15 wt % had been prepared by in-situ dispersion polymerization process. The thermally stimulated current (TSDC) method was used to investigate the charge carrier trap levels and their distribution of the composite films. The TSDC spectra show that pure film has [ABSTRACT FROM AUTHOR]

A type of polyimide/silica (PI/SiO2) copolymer model was established through the dehydration of tetraethyl orthosilicate molecules (TEOS) and bonding to a silane coupling agent. The content of SiO2 was controlled by adjusting the number of molecules which bound to the TEOS. Finally, the silica was formed into a hybrid model (hybrid PI/SiO2) with a small molecule embedded in the PI. The model was optimized by geometric and molecular dynamics and the changes in the model structure, Young's modulus, shear modulus, and glass‐transition temperature (Tg) were analyzed. The results showed that the density and cohesive energy density of the composites could be improved by doping SiO2 in PI. Young's modulus and shear modulus of PI/SiO2 hybrid materials were higher than undoped PI. The tensile strength reached 568.15 MPa when the doping content was 9%. Therefore, the structure design and content control of SiO2 was an effective way to improve the performance of a PI/SiO2 composite. The variation of Tg and tensile strength of PI/SiO2 hybrid composites is consistent with that of PI/SiO2 composite synthesized in real experiment, which will be a convenient method for new material design and performance prediction. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47335. Periodic unit cell of hybrid PI/SiO2 model. [ABSTRACT FROM AUTHOR]