Researches On Dielectric Properties And Energy Storage Of Polymer Matrix Nanocomposites With Graphene And Carbonnanotube Modified By Fluorinated Liquid Crystalline Polymer

The conductive nanofiller/polymer dielectric nanocomposites have broad potential in electronic and electrical field because of the high dielectric constant,excellent flexibility and good mechanical properties.However,due to the large contracts of surface energy between the nanofillers and matrix materials,the conductive fillers tend to agglomerate and nanocomposties produced lots of holes and voids,and micro-capacitors’ numbers decreased,resulting in that nanocomposties exhibited the low energy density.On the other hand,the nanocomposites would present the uneven distribution of electrical field near the nanofiller—matrix interfaces and the complicated interfacial polarization own to the large contracts of electrical properties,leading to decrease the breakdown strength and energy density."Interfacial modifier engineering" is an effective way to overcome above issues.Mesogen-jacketed liquid crystalline polymer(MJLCP)formed the columnar nematic phase and exhibited a semirigid rod feature own to the strong steric effect of side-chain,In addition,the rod length and surface chemistry of the rod could be controlled.In this paper,combined the properties of MJLCP,we choosed the MJLCP as the interfacial modifier of reduced-graphene oxide(rGO)nanosheets and single-walled carbon nanotubes(CNTs).One side,the problems of rGO and CNTs’ dispersity and compatibility can be resloved in the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)(P(VDF-TrFE-CTFE))polymer matrix and P(VDF-CTFE)polymer matrix respectively.Another side,the relationship between interfacial thickness and energy storage of conductive filler/polymer nanocomposites will be investigated in detail.The detail content was as followed:(1)Three kinds of mesogen-jacketed liquid crystalline fluoro-polymer:poly{5-bis[(4-trifluoro-methoxyphenyl)oxy carbonyl]styrene}(PTFMS),poly{2,5-bis[(2,3,4,5,6-pentafluoro)oxycarbonyl]styrene}(PPFMS)and poly{2,5-bis{[3,5-bis(trifluoromethyl)]oxycarbonyl}styrene}(PHFMS)were designed and synthesized.The phase behavior and phase structures of polymers were researched by DSC,POM and XRD.The results showed the all polymers formed the stable columnar nematic phase.In addition,the polymer(PTFMS)is especially the most promising the interfacial modifier of conductive fillers from view point of easy synthesis,low price,high monomer activety and stable liquid crystalline phase.(2)A rigid liquid crystalline fluoride-polymer poly {5-bis[(4-trifluoro-methoxyphenyl)oxycarbonyl]styrene}(PTFMS)is chosen to tailor the shell thicknesses of rGO via tailoring the degree of polymerization.Two core-shell structured reduced graphene oxide(rGO)@rigid-fluoro-polymer conducting fillers with different shell thicknesses are prepared using a surface-initiated reversible-addition—fragmentation chain transfer polymerization method,which are denoted as rGO@PTFMS-1 with a thin shell and rGO@PTFMS-2 with a thick shell.The modified rGO showed the well dispersity and compatibility in the P(VDF-TrFE-CTFE)polymer matrix.The effect of interfacial thickness on the dielectric behavior of the P(VDF-TrFE-CTFE)nanocomposites with rGO and modified rGO is studied in detail.The results demonstrate that the percolation threshold of the nanocomposites increased from 0.68 vol.%to 1.69 vol.%with an increase in shell thickness.Compared to the rGO@PTFMS-1/P(VDF-TrFE-CTFE)composites,the rGO@PTFMS-2/P(VDF-TrFE-CTFE)composites exhibited a higher breakdown strength and a lower dielectric constant,which can be interpreted by interfacial polarization and the micro-capacitor model,resulting from the insulating nature of the rigidpolymer shell and the change of rGO’s morphology.(3)After surface chemistry treatment process,the chain transfer agent was introduced to the surface of single-walled carbon nanotubes(CNTs).Three core-shell structured CNTs@rigid-fluoro-polymer conducting fillers with different shell thicknesses are synthesized via controlling the molar ratio of monomer,initiator and CNTs@CPDB,named as CNT@PTFMS-1,CNT@PTFMS-2 and CNT@PTFMS-3.The thickness of CNT@PTFMS increased from 20 nm to 62 nm.The experiment results indicated that the modified CNT displayed the well dispersity and compatibility in the P(VDF-CTFE)polymer matrix.Compared to the CNT/P(VDF-CTFE)nancomposites,the modified CNT/P(VDF-CTFE)nanocomposites possessed the high dielectric constant,the low dielectric loss and the high percolation threshold.With the increment of thickness,the CNT@PTFMS/P(VDF-CTFE)nanocomposites exhibited the multifarious dielectric behavior due to many influential factors,including interfacial polarization,the micro-capacitor model and electric properties of polymer PTFMS.Such as,the CNT@PTFMS-3/P(VDF-CTFE)showed the highest breakdown strength,while CNT@PTFMS-2/P(VDF-CTFE)presented the highest dielectric constant(25)at1KHz.