Extremely stretchable strain sensors with ultra-high sensitivity based on carbon nanotubes and graphene for human motion detection

Flexible strain sensors have attracted great attention in the field of human health monitoring. Carbon nanotubes (CNTs) and graphene with outstanding electrical conductivity and nanoscale flexibility are often used in the field of stretchable strain sensor. Nevertheless, the combination of high sensitivity and a wide sensing range for stretchable strain sensors seems to be a dilemma. Here, a highly stretchable and sensitive strain sensor was prepared by simply dripping CNTs/graphene conductive composite on a pre-stretching silicon-containing elastomer. Pre-stretching is the key to enhancing the gauge factor (GF) and stretchability of the strain sensor. Compared with the CNTs/graphene coated elastomer without pre-stretching (GF = 4377.23), the GF of the CNTs/graphene coated elastomer with pre-stretching are significantly improved. GF of 28,752.95 (at strain of 23%) is achieved without sacrificing the stretchability at a prestrain coefficient (ε_pre) of 60%. graphene sheets are introduced as the conducting bridge among the adjacent CNTs to significantly improve the stability of the conductive network, thus forming a structure of line-to-plane electrical conduction pathway to provide the sensor with sufficient flexibility. The strain sensor exhibits excellent tensile properties (up to 400% strain) and ultra-high relative resistance change (ΔR/R₀ = 14,719.41) over a wide sensing range (approximately 100% strain) with high durability and repeatability. The pre-stretching CNTs/graphene coated elastomer was then assembled at human joints for detection. The result shows that the strain sensor demonstrates potential applications in wearable electronic products.