A reduced graphene oxide-borate compound-loaded melamine sponge/silicone rubber composite with ultra-high dielectric constant.

Herein, at first, graphene oxide (GO) was prepared by a modified Hummers' method, compounded with borates and then loaded onto a melamine sponge (MS) skeleton by an impregnation-reduction method to obtain a reduced graphene oxide (rGO)-borate compound (rGB)-loaded MS. Then, MS/rGB/silicone rubber (SR) composites were prepared by a vacuum infusion process. Moreover, the microstructures, electrical conductivity, and dielectric properties of the composites were investigated. The results showed that rGO presented a sheet-like structure, compounding with borates produced during the reduction of GO by sodium borohydride. rGB was co-loaded onto the MS skeleton, and a three-dimensional percolation network was successfully constructed in the MS/rGB/SR composite. In addition, there was an efficient synergistic effect between rGO and borates, which significantly improved the dielectric constant of the composites. At the rGO volume fraction of 1.89 vol%, the composite had the volume resistivity of 6.57 × 10 Ω cm, the ultra-high dielectric constant of 2.71 × 10 with the dielectric loss of 1.36 at 1 kHz, and the relatively low percolation threshold of 0.815 vol%. Furthermore, the composite exhibited high compression sensitivity at low compressive strains.