A flexible yet electronically active composite that mimics mechanoreceptor neurons in the human skin is synthesized, generating voltage oscillations whose frequency increases with pressure. By encoding pressure into frequency, the sensor achieves a high pressure sensitivity (<10 Pa). The ability to sense pressure and to amplify signals arises from the robust negative differential resistance of functionalized graphitic flakes in silicone.

A novel type of negative differential resistance (NDR) is demonstrated in composites incorporating graphite nanoparticles in a silicone matrix. The NDR occurs as the electric field breaks the π‐band of graphite, initiating a semimetal‐to‐insulator transition. The current peak is robust and tunable with the graphite concentration. This material can produce flexible electronic amplifiers for bioelectronic applications

We report and systematically study large amplitude piezoresistance spikes in thin composite films under stress. These spikes are characterized by a unique double exponential decay which we demonstrate to be the signature of transient tunnelling currents. We establish an expression that predicts the dynamic conductivity of the composite with only three material parameters and use it to infer the magnitude of applied stress from resistance spikes, thus achieving quasi-instantaneous readout unhindered by viscoelastic relaxation. We demonstrate the proof of principle of ultrafast mechanoreceptors based on this effect by making a sensor array which images pressure at close to cinematic speeds with a sensitivity of 50 Pa.

We report the chemical exfoliation of grapheneoxide from graphite and its subsequent reduction to graphene nanosheets (GN) to obtain highly conducting composites of graphene sheets in a polymer matrix. The effect of using graphite nanoparticles or flakes as precursors, and different drying methods, was investigated to obtain multilayer graphene sheets of atomically controlled thickness, which was essential to optimizing their dispersion in a polystyrene (PS) polymer matrix. In situ emulsion polymerization of the styrene monomer in the presence of GN was performed to obtain thin composite films with highly uniform dispersion and fewer graphene layers when GN were obtained from graphite flakes then freeze drying. The highest electrical conductivity of PS-GN composites was $0.01 S/m for a graphene filling fraction of 2%. The piezoresistance of the PS-GN composites was evaluated and used in pressure sensor arrays with pressure field imaging capability.

No abstract