Study On Polyvinylidene Fluoride- Carbon/cyanate Ester Materials With High Dielectric Constant And Low Loss

High dielectric constant conductor/polymer matrix composites have received extensive attention due to their great potential in many cutting-edge fields. However, their ubiquitous high dielectric loss becomes the bottleneck of restricting their applications. In recent years, researchers begin to design new composites with special spatial structure to obtain high dielectric constant and low dielectric loss, and this is the target of our research reported herein.Firstly, polyvinylidene fluoride(PVDF), acidized multi-wall carbon nanotube(e CNT)and cyanate ester(CE) were used as the components, and a new kind of asymmetrical double-layer composites, PVDF-e CNT/CE, were prepared through coating a PVDF film on the e CNT/CE composite. The conductive and dielectric properties of PVDF-e CNT/CE materials with different content of e CNTs(f) and thickness of PVDF film were studied.Results show that the percolation threshold(fc) of e CNT/CE was 1.6 wt%, when f < fc,with the same f value, the PVDF-e CNT/CE material has similar conductivity and dielectric properties as e CNT/CE composite does, so the conductivity and dielectric properties of PVDF-e CNT/CE materials are not sensitive to the macro-structure in this situation. When f > fc, the thickness of PVDF has obvious influence on the dielectric properties, the dielectric constant of PVDF-e CNT/CE materials initially increases and then decrease as the thickness of PVDF film increases, meanwhile the dielectric loss keeps low values. For example, when f =1.7 wt%, the PVDF-e CNT1.7/CE material of which the thickness of PVDF film is 5 μm has the highest dielectric constant(ε=1699, 1 Hz) among all PVDF-e CNT/CE materials, while its dielectric loss is 5.25 at 1 Hz, which are 10 and2.31×10-2 times of those of e CNT1.7/CE composite. The equivalent circuits of PVDF-e CNT/CE and e CNT/CE materials were built, and the origin behind the amazing dielectric properties were discussed. Results show that the dielectric properties of composites with special spatial structure are closely related to the space charge polarization, which could not be fully reflected by the total capacitance and resistance. Thedielectric properties of PVDF-e CNT/CE composites are resulted from the combined roles of both dielectric properties of PVDF and space charge polarization between PVDF and e CNT/CE.Secondly, to discuss the influence of the micro-structure of PVDF on the dielectric properties of PVDF6-e CNT/CE materials, PVDF6-e CNT1.7/CE materials after treated under different temperature were prepared. Results show that the dielectric constant of PVDF6-e CNT1.7/CE material decreases as the treating temperature increases. The material treated at 20 ℃ and 100 ℃ have the maximum(1564) and minimum(268)dielectric constant at 1 Hz; however, the material treated at 20℃ has higher dielectric loss than others, this is resulted from the different interfacial polarization caused by the phase structure of PVDF under various treating temperature.Finally, the symmetrical three-layer composites PVDF-e CNT/CE-PVDF composites with 0-1-0 sandwich-style were prepared. Results show that with the same total thickness of PVDF, both dielectric constant and loss of PVDF-e CNT/CE-PVDF are lower than PVDF-e CNT/CE. This can be explained that the sandwich-structure weakens the interfacial polarization between PVDF and e CNT/CE layer, that is, the original macro-structure has great effect on dielectric properties of composites.