Piezoresistive and Mechanical Characteristics of Graphene Foam Nanocomposites

We report the piezoresistive and mechanical characteristics of three-dimensional (3D) graphene foam (GF)-polydimethylsiloxane (PDMS) nanocomposites processed by a facile two-step approach. A polyurethane (PU) foam with graphene embedded (and aligned) in the pore walls is pyrolyzed and then impregnated with PDMS to form a GF-PDMS nanocomposite, resulting in a slitlike network of graphene embedded in the viscoelastic PDMS matrix. The interconnected graphene network not only imparts excellent electrical conductivity (up to 2.85 S m^-1, the conductivity of PDMS is 0.25 × 10^-13 S m^-1) to the composite but also enables ultrasensitive piezoresistive behavior. For an applied compressive strain of 10% we report a 99.94% reduction in resistance, with an initial gauge factor of 178, and note that this value is significantly higher than those reported in the literature. Cyclic compression-release tests conducted at different strain amplitudes demonstrate that both the mechanical and piezoresistive responses of the GF-PDMS are fully reversible up to a maximum strain amplitude of 30%. The facile processing, recoverable, and reversible response over 1000 cycles, good hysteresis performance over a range of strain rates, and energy absorption characteristics open new opportunities for GF-PDMS nanocomposites in various applications such as soft robots and human-machine interface technologies.