Lightweight conductive graphene/thermoplastic polyurethane foams exhibited stable piezoresistive sensing signals at a strain of up to 90%.

Strain sensors with high sensitivity are reported in the thermoplastic polyurethane nanocomposites with ultralow graphene loading.

Thermoplastic polyurethane (TPU) based conductive polymer composites (CPCs) with a reduced percolation threshold and tunable resistance-strain sensing behavior were obtained through the addition of synergistic carbon nanotubes (CNT) and graphene bifillers. The percolation threshold of graphene was about 0.006 vol% when the CNT content was fixed at 0.255 vol% that is below the percolation threshold of CNT/TPU nanocomposites. The synergistic effect between graphene and CNT was identified using the excluded volume theory. Graphene acted as a 'spacer' to separate the entangled CNTs from each other and the CNT bridged the broad gap between individual graphene sheets, which was beneficial for the dispersion of CNT and formation of effective conductive paths, leading to better electrical conductivity at a lower conductive filler content. Compared with the dual-peak response pattern of the CNT/TPU based strain sensors, the CPCs with hybrid conductive fillers displayed single-peak response patterns under small strain, indicating good tunability with the synergistic effect of CNT and graphene. Under larger strain, prestraining was adopted to regulate the conductive network, and better tunable single-peak response patterns were also obtained. The CPCs also showed good reversibility and reproductivity under cyclic extension. This study paves the way for the fabrication of CPC based strain sensors with good tunability.

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Conductive hydrogels (CHs) have been highlighted in the design of flexible strain sensors and stretchable triboelectric nanogenerators (TENGs) on the basis of their excellent physicochemical properties such as large stretchability and high conductivity. Nevertheless, the incident freezing and drying behaviors of CHs by using water solvent as the dispersion medium limit their application scopes significantly. Herein, an environment tolerant and ultrastretchable organohydrogel is demonstrated by a simple solvent‐replacement strategy, in which the partial water in the as‐synthesized polyacrylamide/montmorillonite/carbon nanotubes hydrogel is replaced with the glycerol, leading to excellent temperature toleration (−60 to 60 °C) and good stability (30 days under normal environment) without sacrificing the stretchability and conductivity. The organohydrogel exhibits an ultrawide strain sensing range (0–4196%) with a high sensitivity of 8.5, enabling effective detection and discrimination of human activities that are gentle or drastic under various conditions. Furthermore, the organohydrogel is assembled in a single‐electrode TENG, which displays excellent energy harvesting ability even under a stretchability of 500% and robustness to directly power wearable electronics in harsh cold conditions. This work inspires a simple route for multifunctional organohydrogel and promises the practical application of flexible and self‐powered wearable devices in extreme environments.

Highly conductive and stretchable electrospun thermoplastic polyurethane yarns with multi-walled and single-walled CNTs were prepared.

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Flexible strain sensors have attracted tremendous interest due to their potential application as intelligent wearable sensing devices. Among them, crack-based flexible strain sensors have been studied extensively owing to their ultrahigh sensitivity. Nevertheless, the detection range of a crack-based sensor is quite narrow, limiting its application. In this work, a stretchable strain sensor based on a designed crack structure was fabricated by spray-coating carbon nanotube (CNT) ink onto an electrospun thermoplastic polyurethane (TPU) fibrous mat and prestretching treatment to overcome the trade-off relationship. Our sensor exhibited combined features of high sensitivity in a greatly widened workable sensing range [a gauge factor of 428.5 within 100% strain, 9268.8 for a strain of 100–220%, and larger than 83982.8 for a strain of 220–300%], a fast response time (about 70 ms), superior durability (>10 000 stretching–releasing cycles), and excellent response toward bending. The microstructural evolution of CNT branches extending from two edges of the cracks and the excellent stretchability of TPU fibrous mats are mainly related to the remarkable sensing properties. Our sensor is then assembled to detect various human motions and physical vibrational signals, demonstrating its potential applications in intelligent devices, electronic skins, and wearable healthcare monitors.