Semiconductorlike CaCu3Ti4O12 ceramic powders are filled into a poly(vinylidene fluoride‐trifluoroethylene) copolymer matrix to form a flexible composite. The dielectric constant of the composites at 100 Hz reaches more than 600 at room temperature and 1200 at 70 °C, as shown in the figure. The contribution of the heterogeneous relaxation is partially responsible for the high dielectric constant observed here.

In this study, electrical, thermal and mechanical properties of multi-walled carbon nanotubes (CNTs) reinforced Epon 862 epoxy have been evaluated. Firstly, 0.1, 0.2, 0.3, and 0.4 wt% CNT were infused into epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high speed mechanical agitator. Electric conductivity, dynamic mechanical analysis (DMA), three point bending tests and fracture tests were then performed on unfilled, CNT-filled epoxy to identify the loading effect on the properties of materials. Experimental results show significant improvement in electric conductivity. The resistivity of epoxy decreased from 1014 Ω•m of neat epoxy to 10 Ω•m with 0.4% CNT. The experimental results also indicate that the frequency dependent behavior of CNT/epoxy nanocomposite can be modeled by R-C circuit, permittivity of material increase with increasing of CNT content. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 17°C increase in Tg. Mechanical test results showed that modulus increased with higher CNT loading percentages, but the 0.3 wt% CNT-infusion system showed the maximum strength and fracture toughness enhancement. The decrease in strength and fracture toughness in 0.4% CNT/epoxy was attributed to poor dispersions of nanotubes in the composite

Based on the optic and dielectric data acquired under different mechanical and electric conditions and temperature, we show that an orthorhombic phase exists near the morphotropic phase boundary (MPB) (on both the rhombohedral and tetragonal sides of MPB). Because of the proximity of the free energy of this phase to the two other morphotropic phases, i.e., the rhombohedral and tetragonal phases, the experimentally observed phases and phase diagrams near MPB depend crucially on the mechanical and electric conditions as well as the sample history.

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu 3 Ti 4 O 12 (CCTO) particles are used as filler and P(VDF-TrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50 vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50 vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (∼340 K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.

The electromechanical response of poly(vinylidene-fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] copolymers with 9 mol % (CT9) and 12 mol % CTFE (CT12) is reported. The CT12 (at room temperature) exhibits an electrostrictive strain response of more than 5% and a piezoelectric constant d33 of 140pC∕N at a dc bias of 70MV∕m. It is found that about 70% of crystalline regions in P(VDF-CTFE) is at the nonpolar phase and that the CT9 has a crystallinity about 25% higher than the CT12. The difference in electromechanical performance between the CT9 and CT12 cannot be completely explained using the structure/conformation change alone. It is believed that the contribution of the interfacial layers to the polarization and electrostrictive strain response plays an important role.

In spin-cast films of poly(vinylidene fluoride–trifluoroethylene) on metalized silicon substrate, there exists a threshold thickness of crystallization dth, below which the crystallinity drops precipitously. Due to the direct link between the crystallinity and functional properties in the polymer, there is a corresponding large change in the film ferroelectric properties, including the dielectric constant, the polarization level, and polarization switching speed, as the thickness is reduced to below dth. Detail microstructure studies show that this threshold thickness is controlled by the stable crystal lamellar size along the film thickness direction. By varying the film processing condition to reduce the crystal lamellar size in the thickness direction, dth can be reduced markedly. As a result, better ferroelectric responses were obtained in ultrathin films.

The microstructural changes in high-energy electron-irradiated poly(vinylidene fluoridetrifluoroethylene) 68/32 mol % copolymer have been studied by X-ray diffraction, FTIR spectroscopy, and differential scanning calorimetry. The macroscopic polarization response in these materials was investigated by examining the dielectric and polarization behavior in a broad temperature and frequency range. It was found that besides reducing crystallinity in the copolymer film, irradiation produces significant changes in the ferroelectric-to-paraelectric phase transition behavior. The irradiation leads to a reduction in the polar domain size to below a critical size (a few nanometers), resulting in the instability of the macroscopic ferroelectric state and transforming the structure of the crystalline region in the copolymer from a polar all-trans ferroelectric to a nonpolar state represented by a trans-gauche conformation. However, a reentrant polarization hysteresis was observed in the copolymers irradiated with higher doses (>75 Mrad). Therefore, there is an optimized dose that generates a copolymer with a nonpolar structure but relatively high crystallinity whose electromechanical performance is the best. In the copolymers in this optimum dose range, FT-IR data revealed that there is not much change in the molecular conformation with temperature, even as the temperature passes through the dielectric peak, indicating that there is no symmetry breaking in both the macroscale and local level. Although the lattice spacing of the crystalline region along the molecular chain direction discontinuously changes between two special cases, the interchain spacing continuously changes with the irradiation dose, reflecting a strong intrachain coupling between the nonpolar and polar regions. On the other hand, the X-ray data reveal that the crystalline size perpendicular to the polymer chain does not change with irradiation until at doses exceeding 85 Mrad.

An all-organic composite system using newly developed PPy nanoclips is developed. The composites have a uniform microstructure due to the unique preparation process. The composites have a very low percolation threshold (<8 wt.%) and exhibit a high dielectric constant. At room temperature, the composites exhibit a dielectric constant of more than 1,000. At temperatures higher than 98 o C, the composites exhibit a dielectric constant of about 2,000. More interestingly, the high dielectric constant reported here is associated with a loss much smaller than the loss reported for other CDCs using 1-D fillers. It is indicated that a new dielectric relaxation process is induced due to the mixture of PPy with P(VDF-TrFE), whose relaxation time decreases with increasing PPy content. The loss observed in the composites at low temperature including room temperature is mainly determined by this relaxation process rather than the conductivity. If this relaxation process has a strong contribution to the dielectric constant, the widely used percolation formula describing relationship between the dielectric constant and the composite cannot be used.