Although many polymers exhibit excellent dielectric performance including high energy density with high efficiency at room temperature, their electric and dielectric performance deteriorates at high temperatures (~150°C). Here, we show that nanofillers at very low volume content in a high-temperature (high–glass transition temperature) semicrystalline dipolar polymer, poly(arylene ether urea), can generate local structural changes, leading to a marked increase in both dielectric constant and breakdown field, and substantially reduce conduction losses at high electric fields and over a broad temperature range. Consequently, the polymer with a low nanofiller loading (0.2 volume %) generates a high discharged energy density of ca. 5 J/cm3 with high efficiency at 150°C. The experimental data reveal microstructure changes in the nanocomposites, which, at 0.2 volume % nanofiller loading, reduce constraints on dipole motions locally in the glassy state of the polymer, reduce the mean free path for the mobile charges, and enhance the deep trap level.

In order to increase the dielectric constants of polymer-based dielectrics, composite approaches, in which inorganic fillers with much higher dielectric constants are added to the polar polymer matrix, have been investigated. However, high dielectric constant fillers cause high local electric fields in the polymer, resulting in a large reduction of the electric breakdown strength. We show that a significant increase in the dielectric constant can be achieved in polyetherimide nanocomposites with nanofillers whose dielectric constant can be similar to that of the matrix. The presence of nanofillers reduces the constraints on the dipole response to the applied electric field, thus enhancing the dielectric constant. Our results demonstrate that through nanostructure engineering, the dielectric constant of nanocomposites can be enhanced markedly without using high dielectric constant nanofillers.

It is a great challenge in dielectric polymers to achieve a high dielectric constant while maintaining low dielectric loss and high operating temperatures. Here we report that by blending two glassy state dipolar polymers i.e., poly(arylene ether urea) (PEEU, K = 4.7) and an aromatic polythiourea (ArPTU, K = 4.4) to form a nanomixture, the resulting blend exhibits a very high dielectric constant, K = 7.5, while maintaining low dielectric loss (< 1%). The experimental and computer simulation results demonstrate that blending these dissimilar dipolar polymers causes a slight increase in the interchain spacing of the blend in its glassy state, thus reducing the barriers

Advances in modern electronics require the development of polymer-based dielectric materials with high dielectric constant, low dielectric loss, and high thermal stability. Fundamental dielectric theory suggests that strongly dipolar polymers have the potential to realize a high dielect Q3 ric constant. In order to achieve high thermal stability, these polymers should also possess a high glass transition temperature T g . However, it has been observed that in many dielectric polymers the dielectric constant decreases markedly at temperatures below T g due to dipole freezing. This study shows, through combined theoretical and experimental investigations, that nano-structure engineering of a weakly-coupled strongly-dipolar polymer can result in a high energy density polymer with low loss and high operating temperature. Our studies reveal that disorder creates a significantly larger free volume at temperatures far below T g , enabling easier reorientation of dipoles in response to an electric field in aromatic urea and thiourea polymers. The net result is a substantial enhancement in the dielectric constant while preserving low dielectric loss and very high breakdown field. These results here pave the way 1 3 5 7 Please cite this article as: Y. Thakur, et al., Optimizing nanostructure to achieve high dielectric response with low loss in strongly dipolar polymers, Nano Energy (2015), http://dx.doi.org/10.1016/j.nanoen.2015.06.021for engineering the nanostructure to create high energy density polymers with low loss and high operating temperature.

For energy storage applications, it is critical that the dielectric material possesses low losses, especially the conduction losses, which could become significant at high temperatures and high electric fields. We investigate the conduction at fields up to 100 MV/m and high temperatures in a semi-crystalline poly(tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride) terpolymer which has been shown to be attractive for high energy density capacitors. Experimental results show that the insulating nanofillers are very effective in reducing the conduction current, i.e., a more than two orders of magnitude reduction in conduction can be achieved with less than 1 wt. % (&lt;0.5 vol. %) of Al2O3 nanofillers. Experimental measurements are compared with multiscale simulations, which shows that the dominant conduction mechanism, i.e., carrier hopping in the polymer, is markedly reduced owing to a large decrease in the mobile carrier concentrations and increased trap depth, caused by the nanofillers.

Articles you may be interested inAromatic poly(arylene ether urea) with high dipole moment for high thermal stability and high energy density capacitors Appl. Phys. Lett. 106, 202902 (2015); 10.1063/1.4921485Meta-aromatic polyurea with high dipole moment and dipole density for energy storage capacitors Appl. Phys. Lett. Enhanced electric breakdown strength and high energy density of barium titanate filled polymer nanocompositesHigh energy density polymer materials are desirable for a broad range of modern power electronic systems. Here, we report the development of a new class of polymer dielectrics based on polyurea and polythiourea, which possess high thermal stability. By increasing the dipole density, the dielectric constant of meta-phenylene polyurea and methylene polythiourea can be increased to 5.7, compared with aromatic polyurea and aromatic polythiourea, which have a dielectric constant in the range of 4.1-4.3. The random dipoles with high dipolar moment and amorphous structure of these polyurea and polythiourea based polymers provide strong scattering to the charge carriers, resulting in low losses even at high electric fields. Consequently, this new class of polymers exhibit a linear dielectric response to the highest field measured (>700 MV/m) with a high breakdown strength, achieving high energy density (>13 J/cm 3 ) with high efficiency (>90%). V C 2015 AIP Publishing LLC.

Developing dielectric polymers with higher dielectric constant without sacrificing loss and thermal stability is of great importance for next generation of high energy density capacitors. We show here that by replacing the CH 2 group in the aromatic polyurea (ArPU) with the polar ether group, thus raising the dipole moment of the molecular unit, poly(arylene ether urea) (PEEU) shows an increased dielectric constant of 4.7, compared with 4.2 of ArPU. Moreover, PEEU maintains the low dielectric loss and is thermally stable up to 250 C. As a result, the polymer delivers 13 J/cm 3 discharged energy density at room temperature and 9 J/cm 3 at 120 C. The high quality films perform well in terms of both breakdown strength (at 700 MV/m at room temperature) and leakage current from room temperature to elevated temperature. At 120 C, the breakdown strength is 600 MV/m and the conductivity is 1.58 Â 10 À14 S/cm measured under 100 MV/m. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4921485]Dielectric capacitors with high energy density, low loss, and high operating temperature are desired for a broad range of applications such as hybrid electrical vehicles (HEVs), pulse power weapon systems, and switch mode power supplies. 1-5 Compared with ceramic capacitors, polymer-film capacitors possess several advantages such as high dielectric strength, high energy density and low dielectric loss. However, for the traditional polymer capacitors such as biaxially oriented polypropylene (BOPP), the dielectric constant is low (K % 2.2), the energy density is limited to 5 J/cm 3 , and the maximum operating temperature is lower than 100 C. 3 Low energy density leads to significant volume and hinders the miniaturization of electronic devices. In addition, low operating temperature limits the broad applications of capacitors. In many of these widely used linear dielectrics like BOPP, conduction loss becomes more significant at higher applied fields. 6,7 Usually, these losses increase exponentially with the electric field, and cause Ohmic heating of the capacitors. 2,6-8 This results in the need to have a cooling system to avoid overheating the BOPP film capacitors. For example, in hybrid electric vehicles, an extra cooling loop has to be introduced in the BOPP capacitor banks in order to prevent a runaway temperature increase caused by the conduction loss heating.In an effort to increase the energy density, PVDF-based polymers with high dielectric constant were developed which showed 25 J/cm 3 energy density. 4,9,10 However, these polar polymers with strongly coupled dipoles exhibit pronounced polarization hysteresis at high electric fields which leads to high loss.Several studies have been conducted earlier on ArPU for dielectric applications due to its relatively high dielectric constant ($4.2), low loss ($1%), and high thermal stability (>150 C). [11][12][13][14][15] In this letter, we show that replacing the CH 2 group in aromatic polyurea (ArPU) (Fig. 1), by the polar ether group, can lead to an increase in the dielectric co...

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