Enhanced dielectric and mechanical properties in chlorine-doped continuous CNT sheet reinforced sandwich polyvinylidene fluoride film

The fabrication and performance of a novel continuous carbon nanotube (CNT) sheet reinforced polyvinylidene fluoride (PVDF) film with sandwich structure are firstly reported. Continuous CNT sheet fabricated by means of floating catalyst chemical vapor deposition was used. A dispersion-free technique for the sandwich composite film was adopted. For the prepared film with sandwich structure, CNT sheet/PVDF acts as a highly conductive layer to raise dielectric permittivity, while two PVDF films at top and bottom of composite are used as insulating layers to suppress dielectric loss. Thionyl chloride doping treatment was done for CNT sheet and the effects of dopant on chemical composition, structure and properties of CNT sheet and composite film were investigated. Resulted from unique performances of the modified CNT sheet and strong interfacial polarization process, the sandwich composite film possesses excellent dielectric and mechanical properties, where dielectric permittivity of 32, dielectric loss of 0.08, tensile strength of 90 MPa and modulus of 3 GPa are shown for optimized chlorine-doping duration time and composite composition. Such composite material and structure have potential applications in hybrid capacitors due to high permittivity, low dielectric loss, good flexibility and ease of processability.