High Strength Flexible E-skin Based On Silicone Composites

Recently,various piezoresistive composites with good flexibility have been developed as sensing materials for flexible strain sensors.External forces will be applied to strain sensors when they are used in some circumstances such as wrist bending,etc.However,conventional flexible composites may fail upon being subjected to external forces since they have low strength and are unable to protect the inner vulnerable structure of flexible sensors.In this paper,the reduced graphene oxide-coated glass fabric(RGO@GF)/silicone composite is fabricated and used to make high-performance structural flexible strain sensors.The composite is not only flexible and sensitive to strain,but also exhibits the high tensile strength needed to maintain the structural integrity of the flexible strain sensor.Silicone resin and GF are employed to provide flexibility and high strength,respectively.By coating RGO on the surface of GF,the nonconductive GF becomes conductive,which renders the piezoresistive behavior and strain-sensing ability to the RGO@GF/silicone composite.The as-prepared structural flexible sensor not only possesses a good strain sensitivity,but can also maintain its structural integrity until the applied external force is over 800 N,while the conventional flexible strain sensor fails upon being subjected to an external force of only 5 N.Moreover,the as-prepared structural flexible strain sensors are applied to monitor wrist movement and breathing to demonstrate its applicability.Although RGO@GF/silicone composite has excellent mechanical properties,but it has poor stretchability,and has a large difference in mechanical properties from human skin,and cannot recognize the location and magnitude of pressure like skin.Besides the prominent tactile sensing ability,human skin is also known with a unique mechanical behavior-the combination of an excellent softness with certain stretch-ability and a strain-limiting effect to prevent damage from excessive strain.In this work,the fabrication of a stretchable e-skin truly mimicking the tactile and mechanical behavior of human skin is demonstrated.Here,high performance carbon fiber with quasi-sinusoidal shape is designed to serve as the electrode materials and reinforcement filler simultaneously,which renders the fabricated e-skin a typical J-shape stress-strain curve similar as human skin.Importantly,the tensile strength and failure strain of the e-skin are controllable in the range of 1.2-6.2 MPa and 10-70% by adjusting the content and shape of the carbon fiber electrode,which match well with those of human skin.At the same time,carbon black/silicone composite with excellent piezo-resistive performance is employed as the mechanical stimuli sensing material,which provides the super softness,large stretch-ability,high strain sensitivity and long-term reliability desired for the e-skin.The e-skin fabricated with 5×5 tactile pixels exhibits the capability for spatiotemporal recognition of the location and magnitude of contact forces,and demonstrates the applicability in dynamic stress distribution monitoring.Considering the super soft but strong characteristics,combined with the spatial tactile sensing ability,the stretchable e-skin is highly promising in robotics and prosthetics,etc.