Rapid-Response, Widely Stretchable Sensor of Aligned MWCNT/Elastomer Composites for Human Motion Detection

Abstract

We studied the use of carbon-nanotube-(CNT)-based strain sensors as components of a textilebased, wearable sensing system for real-time motion detection. In the stretchable sensor, millimeter-long multiwalled CNTs (MWCNTs) are unidirectionally aligned and sandwiched between elastomer layers. We synthesized urethane resin to make the elastomer, which exhibits low elasticity and an affinity for human skin. The aligned CNT layer was formed by stacking CNT webs drawn from a spinnable CNT forest. The stretchable sensor can be stretched up to 200% and exhibits a short sensing delay of less than 15 ms. The gauge factor exceeds 10, which indicates high sensitivity. Moreover, the device is thin and as soft as human skin. The demonstrated flexibility and conformable nature make this material ideally suited for wearable sensors, specifically for a textile-based, wearable, real-time, human body motion-sensing application.

Stretchable sensors for environmental monitoring

“…One-dimensional nanomaterials, such as CNTs 46 and Ag NWs, 47,48 are probably the most prevalent constituent materials for stretchable environmental sensors. Because of the high aspect ratio of these 1D materials, when either randomly or deterministically dispersed and embedded in an elastomeric polymer matrix, they form a stretchable conductive network that can reconfigure its shape under mechanical loading.…”

“…In these nanocomposites, the network paths are rearranged when strain is applied to retain the electrical continuity. Nanomaterial dopants such as graphene, carbon nanotubes (CNTs), 46 and metallic and semiconducting nanowires (NWs) [47][48][49][50] could be used in these applications.…”

Carbon Nanotubes for Mechanical Sensor Applications

“…Macroscopic approaches are not capable of testing structures of single CNTs; instead, they focus on the creation of macroscopic structures as films, dog bones, or yarns which are tested using macroscopic tensile testing devices Besides this, substrate bending (as shown in Figure ) and three‐ or four‐point bending setups are discussed as alternatives. Besides such classical approaches, studies are presented in which CNT compounds are directly attached to the human body to sense the action of knees, fingers, and facial muscles—which also strains or bends the substrate. Films and foils are fabricated, e.g., using spraying of CNT compounds on polydimethylsiloxane or polyethylene terephthalate, coating rubber by hand, by drying CNTs in suspension, or by dispensing CNTs on carrier foils .…”

“…Dog bones are created by embedding CNTs in polymers based on polysulfone, polyurethane, polyvinylidene fluoride, polymethyl methacrylate, polyimide, or epoxy to name only some, which are then cut into appropriate shapes and characterized. Finally, yarns are spun, e.g., using manually processed CNT arrays, dry‐spinning processes, by piston spinning of CNT‐polycarbonate yarns, or by processing CNT forests grown on a Si wafer …”

“…In a similar way, CNT ropes can serve as electronic force sensors, whereas CNT films are used as strain gauges to sense the movement of a piece of human skin or the body . Here, the morphology of the particular CNT solid governs the possibilities to intentionally alter the electronic properties of the CNT material by materials engineering (e.g., covalent and noncovalent functionalization of CNT sidewalls in external grooves) or in the context of sensoric function (e.g., adsorption of gas molecules in interstitial channels, cf.…”