The Design, Preparation And Electromechanical Property Of Graphene Dielectric Elastomer Composites

Dielectric elastomer (DE) is a kind of electroactive polymer, which can induce electric field and convert electrical energy into mechanical energy. However, the key issue to develop DE is to improve the dielectric constant and keep low dielectric loss and elastic modulus simultaneously. A key limitation for the practical application of dielectric elastomer actuators (DEAs) is the requirement of high operating electric field, which could be harmful to humans and damage equipment, particularly in biological and medical fields. Getting a large actuated strain at a low electric field is the biggest challenge for DEAs.The graphene oxide nanosheets (GO)-encapsulated carbon nanosphere (GO@CNS) hybrids were fabricated for the first time via π-π interaction and hydrogen bonding interaction. CNS@GO hybrids as dielectric fillers were blended with carboxylated nitrile rubber (XNBR) through latex mixing. The directional distribution of GO@CNS hybrids around carboxylated nitrile rubber (XNBR) latex particles was realized during latex compounding. The thermally reduced GO (RGO)@CNS/XNBR composites with high performance were then obtained from GO@CNS/XNBR by vulcanization and in situ thermal reduction. The filling effect of CNS and the formation of the segregated filler network of GO@CNS decreased the addition of GO and the percolation threshold, and thus decreased the elastic modulus of the composites. In situ thermal reduction of GO@CNS/XNBR composites was required to restore the graphite structure of GO and increase the interfacial polarization ability of GO@CNS, and thus improved the dielectric performance of the composites. The results showed that k at103Hz obviously increased from28for pure XNBR to400for the composite with0.75vol.%of RGO@CNS hybrids. Meanwhile, the composite with0.75vol.%of RGO@CNS hybrids retained low dielectric loss (<0.65at103Hz). In addition, the elastic modulus only mildly increased with the addition of0.75vol.%of the hybrids, retaining good flexibility of the composites. More interestingly, the actuated strain at7kV/mm obviously increased from2.69%for pure XNBR to5.68%for the composite with0.5vol.%of RGO@CNS, and the actuated strain at a lower electric field (2kV/mm) largely increased from0.23%for pure XNBR to3.06%for the composite with0.75vol.%of RGO@CNS, much higher than that of other DEs reported in previous studies.Poly(dopamine) encapsulated graphene oxide (GO-PDA) nanosheet was synthesized by means of self-polymerization of dopamine on GO surface. GO-PDA as dielectric filler was blended with XNBR through latex mixing, and then the GO-PDA/XNBR composites with controllable dielectric and actuated performance were prepared by regulating the concentration of dopamine. The introduction of PDA on the surface of GO prevented the restack of GO nanosheets in the matrix. The PDA shell thickness could be controlled accurately when the concentration of dopamine was below0.75g/L. As a result, with the increase of thickness of PDA shell, the insulating property and breakdown strength of GO-PDA/XNBR composites were improved, and dielectric loss and elastic modulus decreased obviously. The GO-PDA/XNBR composite has good integrated performance containing dielectric property, insulating property and actuation performance, when the concentration of dopamine is within0.5g/LThe preparation of RGO@CNS/XNBR dielectric elastomer composite with high dielectric constant, low dielectric loss, low elastic modulus and large actuated strain at a low electric filed and GO-PDA/XNBR dielectric elastomer composite with controllable dielectric and actuated performance facilitates the application and development of dielectric elastomer in biological and medical fields, where a low electric field is required.