Preparation And Research Of Dielectric Pvdf Composites Based On Hybrid Filler Structure Design

Preparation of dielectric polymer composites by adding fillers with high dielectric constant into polymer matrix has attracted extensive attention.With many advantages,such as various structure,easy prepared and low cost,dielectric polymer composites having broad application in electronic and electrical fields.Common dielectric fillers include ceramic fillers,such as:Barium titanate?BT?,Silicon carbide?SiC?,Aluminium oxide?Al₂O₃?,etc.and carbon-based conductive fillers,such as:Graphene oxide?GO?,Carbon nanotubes?CNTs?,Polypyrrole?PPy?.The dielectric constant of the composites can be improved by directly introducing single filler into the polymer matrix,however,the composites are difficult to be applied because of the high dielectric loss.Therefore,preparing dielectric polymer composites with better dielectric properties based on filler hybridization is very important for the development of electronic devices.The research of this paper is focus on the composition and structure of hybrid fillers impact on the dielectric properties of poly?vinylidene fluoride??PVDF?.First of all,the effect of PPy@GO hybrid fillers on the dielectric properties of PVDF was studied.By constructing multi-interface polarization structure through in situ intercalation polymerization between PPy and GO,the influences of filler interface and filler dispersion on the dielectric properties of composites were investigated.Moreover,by introducing micro and nano BT particles,a number of hybrid packing assemblies were designed,and the effects of composition and arrangement of hybrid fillers on the dielectric properties of composites were studied.The results obtained in this paper are listed as follows:?1?PPy@GO hybrid fillers were prepared by in situ intercalation polymerization firstly,then introduced them into PVDF matrix to prepare ternary dielectric nanocomposites via solution compounding.The microstructure of the PPy@GO hybrid fillers were studied by SEM and other characterization methods.It was found that the polymerization of PPy particles on the GO surface effectively exfoliated the GO sheets and the GO sheets were partly reduced.The melting and crystallization behavior of the composites were studied by DSC.It was found that the PPy@GO hybrid fillers showed nucleation effect on the crystallization of PVDF,but they did not induced the formation of the?polar crystals in PVDF.The electrical properties of the composites were studied by the broadband dielectric resistance spectrometer.It was found that the PPy@GO hybrid fillers had a certain promotion effect on the AC conductivity of the composites,and the PVDF/PPy@GO composite with the highest filler content is still in the insulating state,which avoided the great dielectric loss caused by the conductive filler network.As for dielectric properties,PPy@GO hybrid fillers greatly improved the dielectric constant of the composites by inducing multi-interface polarization,at the same time,the dielectric loss of the composites were controlled because of the good dispersion of the fillers.With same filler content,the dielectric constant and dielectric loss of the PVDF/10PPy composites were 74.7 and 0.42,while the PVDF/10PPy@GO composite were 306.4 and 0.36,respectively.?2?BT@PPy-GO hybrid fillers were synthesized by one-step process through directional filler hybridization,then introduced them into PVDF matrix to prepare dielectric nanocomposites via solution compounding.The microstructure of BT@PPy-GO hybrid fillers were studied by SEM and other characterization methods.It was found that the electrostatic interaction between GO and PPy could induce the BT@PPy particles adsorb on the GO surface and avoid the filler aggregation.The melting and crystallization behavior of the composites were studied by DSC.It was found that the BT@PPy-GO hybrid fillers had nucleation effect on the crystallization of PVDF and it could partly induced the formation of?polar crystals.The electrical properties of the composites were studied by the broadband dielectric resistance spectrometer.It was found that the BT@PPy-GO hybrid fillers could not only enhance the internal charge transfer ability,but also ensured the insulation state of the composites.The AC conductivity of the PVDF/BT@PPy-GO composite with the highest filler content was about 10^-9 S/cm.As for dielectric properties,GO could help BT@PPy particles to disperse and reduce the dielectric loss of the composites,but it also brought the non-negligible dielectric structure loss to the composites.At the high filler content,the BT@PPy-GO hybrid fillers has a good dispersion in the system.The dielectric constant of the composites were improved and the dielectric loss were also effectively controlled.While at the low filler content,the contact between BT@PPy particles was limited,the dielectric loss reduced by GO less than the dielectric loss caused by itself.In the case of same dielectric constant,the PVDF/BT@PPy composites had lower dielectric loss than the PVDF/BT@PPy-GO composites.The dielectric breakdown strength measurement was applied to study the breakdown strength of the composites.It was found that the two-dimensional GO sheets had the effect of deflecting crack direction,and the PVDF/BT@PPy-GO composites has a higher breakdown strength at the lower filler content.However,when the content of hybrid fillers was high,the breakdown strength of PVDF/BT@PPy-GO composites dropped sharply when GO constructed three dimensional network inside the composite.?3?h-MBT@PPy hybrid fillers were synthesized by hydroxylation of micro BT?MBT?particles and combined with PPy,then introduced them into PVDF matrix to prepare dielectric nanocomposites via solution compounding.The microstructure of the hybrid fillers were studied by SEM and other characterization methods.It was found that hydroxylation treatment increased the hydroxyl content of the MBT particles surface.The obtained h-MBT particles had stronger interaction with PPy,and the Py monomers were more easily polymerized on the surface of the h-MBT particles.The melting and crystallization behavior of the composites were studied by DSC,and it was found that the h-MBT@PPy hybrid fillers had nucleation effect on PVDF.Because the surface of the h-MBT particles were covered by PPy,there were no direct contact between the hydroxyl group and PVDF,and none?polar crystal was formed in the composites.The electrical properties of the composites were studied by the broadband dielectric resistance spectrometer.Compared with the MBT@PPy hybrid fillers,the h-MBT@PPy hybrid fillers had weaker AC conductivity enhancement of the composites.The excellent electric conductivity of the PVDF/MBT@PPy composites was derived from the local conductive network which were lapped in the PVDF matrix.As for dielectric properties,because of the volume exclusion effect,the PPy conductive network was easily formed in the PVDF/MBT@PPy composites,and the dielectric loss was difficult to control.However,in the PVDF/h-MBT@PPy composites,PPy were polymerized around the h-MBT particles and no conductive network formed.The dielectric constant increases gradually with the increase of the filler content,and the dielectric loss maintained at low level of the PVDF matrix.The dielectric constant of the PVDF/20MBT@PPy composite is 211.7,and the dielectric loss is up to 0.7.After efficiently filler hybridization,the dielectric constant of the PVDF/20h-MBT@PPy composite decreases,but the dielectric loss reduces to a very low level of 0.06,almost equivalent to the PVDF matrix.