Abstract
Flexible pressure sensors have attracted tremendous research interests due to their wide applications in wearable electronics and smart robots. The easy-to-obtain fabrication and stable signal output are meaningful for the practical application of flexible pressure sensors. The graphene/polyurethane foam composites are prepared to develop a convenient method for piezo-resistive devices with simple structure and outstanding sensing performance. Graphene oxide was prepared through the modified Hummers method. Polyurethane foam was kept to soak in the obtained graphene oxide aqueous solution and then dried. After that, reduced graphene oxide/polyurethane composite foam has been fabricated under air phase reduction by hydrazine hydrate vapor. The chemical components and micro morphologies of the prepared samples have been observed by using FT-IR and scanning electron microscopy (SEM). The results predicted that the graphene is tightly adhered to the bare surface of the pores. The pressure sensing performance has been also evaluated by measuring the sensitivity, durability, and response time. The results indicate that the value of sensitivity under the range of 0–6 kPa and 6–25 kPa are 0.17 kPa−1 and 0.005 kPa−1, respectively. Cycling stability test has been performed 30 times under three varying pressures. The signal output just exhibits slight fluctuations, which represents the good cycling stability of the pressure sensor. At the same stage, the response time of loading and unloading of 20 g weight turned out to be about 300 ms. These consequences showed the superiority of graphene/polyurethane composite foam while applied in piezo-resistive devices including wide sensitive pressure range, high sensitivity, outstanding durability, and fast response.
Highlights
With the rapid development of the information technology, flexible pressure sensors have been extremely concerned due to their potential in human machine interface, flexible robots, wearing electronic equipment, and flexible electronic skin [1–15]
The chemical structure as well as the micro morphologies were observed with Fourier Transform infrared spectroscopy (FTIR) and Scanning electronic microscope (SEM)
The pressure sensing performance such as sensitivity, recognition ability to different pressures, cycling stability, and response time were systematically investigated by using the electrochemical workstation, RLC digital electric bridge, digital display force gauge, and relative tension and compression testing bench
Summary
With the rapid development of the information technology, flexible pressure sensors have been extremely concerned due to their potential in human machine interface, flexible robots, wearing electronic equipment, and flexible electronic skin [1–15]. A typical method to prepare the flexible pressure sensors is to construct a composite with elastomer material as the matrix and the conductive filling materials. The piezo-resistive materials were mainly fabricated with conductive particles filled with elastomer composites. The deformation of the elastomer would force the conductive particles to form another electrical conductive network. The deformations of these solid materials required overcoming strong energy to move the molecular chains, which seriously restricts the sensitivity of the manufactured piezo-resistive materials [24–26]. Substrate with lower Young’s modulus possesses stronger deformation ability which significantly contributes the sensitivity. Polyurethane (PU) foam, which is an elastic material with large amount of through-pore structures and exhibiting low Young’s modulus and high resilience, is an ideal candidate for high performance substrate for piezo-resistive sensors
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