Vertically aligned carbon nanotubes/graphene/cellulose nanofiber networks for enhancing electrical conductivity and piezoresistivity of silicone rubber composites

The directional arrangement of a conductive filler is an effective method to improve electrical conductivity of composites. In this paper, aqueous dispersions of carbon nanotubes and graphene were prepared by high-pressure microfluidization technology. After mixing cellulose nanofiber into these dispersions, vertically aligned carbon nanotubes/graphene network foams were prepared using an ice-template assembly method, to which liquid silicone rubber was filled to obtain carbon nanotubes/graphene/silicone rubber composites. Polymethylhydrosiloxane was grafted with 3-(trimethoxysilyl) propyl methacrylate and the resultant copolymer was used as a coupling agent to improve interface interaction between silicone rubber and filler. With increasing carbon nanotubes content, the electrical conductivities of the foams and composites increased. The composite prepared with 4 g CNT and 1 g graphene aqueous dispersions had the conductive percolation threshold of 0.08% and exhibited high conductivity at low filler content. The addition of the copolymer increased the compressive strength of the composites. The composite prepared with 1 g CNT and 4 g graphene aqueous dispersions was encapsulated in an insole as a piezoresistor to effectively detect the number of pedestrian steps, and had a stable output of electrical signal. This work provides a method for preparing conductive silicone rubber composites with low conductive percolation threshold and excellent piezoresistivity.