Temperature Sensitive Behavior Of Functionalized Graphene And PVDF Nano-composites

At present, graphene has been a hot research topic because of its excellentelectrical conductivity and thermal conductivity. However, its dispersion is not good,which limits its further research and application. In order to improve the dispersionof graphene, and strengthen its combination with the PVDF matrix, styrenesulfonate is grafted, and nano-silver is loaded on the surface of graphenerespectively by the non-covalent bond function method in this paper. Then, thenano-composites are prepared through dispersing the functionalized graphene in thePVDF matrix by the solution mixing method. Moreover, effects of the kind andaddition amount of the functional graphene on the electrical conductivity andthermo-sensitivity of the PVDF-based nano-composites are investigated.Research results showed that under the condition of excess styrene sulfonate,the mass ratio of graphene oxide and initiator was1:2, and the grafting time was18h, the grafting efficiency of sodium styrene sulfonate on the surface of graphenewas highest, which was up to54.5%. This kind of functionalized grapheme could bewell dispersed in the solution. In addition, it was better for the nano-silver particlesloading on the surface of graphene under the reaction temperature was80to85℃,the mass ratio of graphene oxide and silver nitrate was1:0.72, and the reaction timewas4~5h. The loading nano-silver particles were also helpful for dispersinggraphene uniformly in the solution.The two kinds of functionalized graphene could be well dispersed in the PVDFmatrix, and their addition had little effects on the thermal stability and the degreeof crystallinity of the PVDF material. Moreover, addition of this three kinds ofgraphene improved the electrical conductivity of the composites significantly. Thepercolation threshold of graphene in PVDF composite is8%, and the conductivity atthat point is9.2×10-4S/cm; The percolation threshold of styrene sulfonate graftedgraphene in PVDF composite is5%, and the conductivity at that point is6.6×10-4S/cm; That of nano-silver loaded graphene in PVDF composite is just4%, and theconductivity at that point is up to7.2×10-4S/cm.The three kinds of PVDF nanocomposites filling with graphene, styrenesulfonate grafted graphene and Ag loaded graphene respectively, have negativetemperature coefficient (NTC) characteristics. Moreover, the maximum of NTCintensity of the three PVDF nano-composites are around their percolation thresholds.The conduction mechanism of these composites is governed by the hoppingmechanism. The activation energy Eaand the transition energy Ehreduce with theincrease of the filler content. In addition, thermal constants of the three kinds of PVDF composites are all above, and their temperature coefficients ofresistance-α are more than0.18K-1under their percolation thresholds.