High performance dielectric composites by latex compounding of graphene oxide-encapsulated carbon nanosphere hybrids with XNBR

A novel dielectric composite with high dielectric constant (k), low dielectric loss, low elastic modulus and large actuated strain at a low electric field was prepared by a simple, low-cost and efficient method. The graphene oxide nanosheet (GO)-encapsulated carbon nanosphere (GO@CNS) hybrids were fabricated for the first time via π-π interaction and hydrogen bonding interaction by simply mixing the CNS and GO suspension. The assembly of GO@CNS hybrids around rubber latex particles was realized by hydrogen bonding interaction between carboxylated nitrile rubber (XNBR) and GO@CNS hybrids during latex compounding. The thermally reduced GO (RGO)@CNS/XNBR composites were then obtained from GO@CNS/XNBR by vulcanization and in situ thermal reduction, resulting in the formation of a segregated filler network. The results showed that k at 10³ Hz obviously increased from 28 for pure XNBR to 400 for the composite with 0.75 vol% of the hybrids because of the formation of a segregated filler network and the increased interfacial polarization ability of the hybrids after in situ partial thermal reduction. Meanwhile, the composite with 0.75 vol% of the hybrids retained low conductivity (10^-7 S m^-1), resulting in low dielectric loss (<0.65 at 10³ Hz). In addition, the elastic modulus only mildly increased with the addition of 0.75 vol% of the hybrids, retaining the good flexibility of the composites. More interestingly, the actuated strain at 7 kV mm^-1 obviously increased from 2.69% for pure XNBR to 5.68% for the composite with 0.5 vol% of RGO@CNS, and the actuated strain at a lower electric field (2 kV mm ^-1) largely increased from 0.23% for pure XNBR to 3.06% for the composite with 0.75 vol% of RGO@CNS, which is much higher than that of other dielectric elastomers reported in previous studies, facilitating the application of the dielectric elastomer in biological and medical fields, where a low electric field is required.