To obtain the high dielectric constant and superparamagnetic composites for application in dielectric energy storage capacitors and other electromagnetic devices, the Fe3O4 nanoparticles have been embedded into polyvinylidene fluoride (PVDF) polymer. As expectation, a distinct percolation effect has been found in these composites, because of the good conductivity of Fe3O4 nanoparticles. The composites exhibit great increase of the dielectric constants and conductivities near the percolation threshold. The maximum of dielectric constant is up to 5240 at 100 Hz, which is the highest value reported to date among the PVDF based percolative composites. Meanwhile, the dielectric loss is controlled in the range of 0–2.2. These composites also exhibit superparamagnetic with the presence of Fe3O4 nanoparticles. The maximum of saturation magnetization is 30.8 emu/g. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
To investigate the stretching effect of polymer-based composites, the films of polyvinylidene fluoride (PVDF) and nickel (Ni) composites were stretched at 120°C. It was found there was an abrupt increase in dielectric constants and conductivities with stretching ratio (SR). In comparison to percolation effect caused by involvement of conductive particles, it was named as stretching-induced percolation here. When SR was near the threshold, dielectric constants showed 17 times improvement and conductivities displayed four to five orders of magnitude enhancement at 100 Hz in low Ni fraction composites. And the reasons of stretching-induced percolation were analyzed here. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
To further understand crystallization behaviors above the melting temperature (Tm), the morphologies and structure of ferroelectric poly(vinylidene fluoride/trifluoroethylene) [P(VDF–TrFE); 70/30] copolymer films at different temperatures were studied by atomic force microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). We found that there was a structural change in the P(VDF–TrFE) copolymer film above Tm, which corresponded to the transition from tightly arrayed grains to fiberlike crystals. For the samples annealed above Tm, heat treatment reduced the density of gauche defects and caused a better arrangement of the crystalline phase. So those samples were in the ferroelectric phase without gauche defects, with one sharp diffraction peak reflected in the XRD curves. It was helpful to further make clear the thermal behaviors from the melts of the P(VDF–TrFE) copolymers and discuss their application under higher temperatures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
The structural changes of irradiated and recrystallized copolymers of vinylidene fluoride and trifluoroethylene [P(VDF-TrFE)] (80/20) copolymers have been investigated through IR spectra, X-ray, and DSC. It is found that recrystallization has a reverse effect on irradiated P(VDF-TrFE) copolymers, by which the irradiated samples are turned back to original nonirradiated state partially. During recrystallization, trans-gauche sequences are replaced by all-trans conformation gradually and the irradiated P(VDF-TrFE) (80/20) copolymers change from nonpolar phase to polar one. The average crystallite size of polar phase is larger than that in irradiated samples, and the difference between recrystallized and irradiated samples reduces gradually with irradiation dosage. The CC and conjugated CC bonds are also found in the recrystallized-irradiated P(VDF-TrFE) (80/20) due to rearrangement of broken bonds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4258–4263, 2006
