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• CB particles were decorated on PDMS foam to fabricate a flexible porous piezoresistive sensor. • The sensor possesses a very high linear working range (up to 91%). • A fast response time (45 ms) and superior durability (>15000 cycles) have both been achieved. • The sensor possess an excellent hydrophobic property (water contact angle up to 149°). • The CB/PDMS foam can also be used for oil/water separation. The achievement of favorable pressure sensor integrated with large linear working range, high sensitivity and excellent response durability is still a great challenge for flexible and wearable piezoresistive materials. In this paper, a facile and scalable strategy is proposed to fabricate a porous foam sensor based on carbon black/polydimethylsiloxane (CB/PDMS). CB particles were decorated onto the surface of the cell walls and some particles were embedded into PDMS matrix after the ultrasonication treatment. The density and porosity of the foam are 0.13 g/cm3 and 76.1%, respectively. A very high linear working range (up to 91%), an excellent response stability, a fast response time (45 ms), and a superior durability (>15000 cycles) are achieved synchronously. Here, the large linear sensing range is mainly related to the nice CB conductive network on the cross-linked PDMS foam and the high modulus and elasticity of the composite material, which ensure the homogeneous deformation of the foam under compression. It is worth noting that the response behavior of CB/PDMS foam is maintained well even in water owing to its excellent hydrophobic property (water contact angle up to 149°), indicating that this material can be used as a waterproof piezoresistive sensor. Our CB/PDMS foam is then assembled as a wearable sensor, and it exhibits nice capability of monitoring human body motions, such as the bending of fingers and elbow, walking, jumping and squatting, etc. The porous foam sensor also has a good oil/water separation ability, showing a multifunctional characteristic. [ABSTRACT FROM AUTHOR]

[Display omitted] • PDA and PPy nanofibers coated foam with narrow orifice structure was developed. • The multi-scale closure mechanism contributed to an ultra-high sensitivity. • The sensor exhibits fast response time, high linearity and excellent stability. • The foam sensor can detect walking, running, yoga postures and sleeping positions. Commercial foam based piezoresistive sensors are promising flexible sensing units for wearable devices, while they suffer from relative low sensitivity, especially in low pressure range. Herein, inspired by scorpion slit organs, multi-scale closure piezoresistive sensors are developed by self-polymerization of a polydopamine (PDA) layer and a polypyrrole nanofibers (PPy NFs) layer on polyurethane (PU) foam, and constructing a macroscopic narrow orifice configuration (NOC), which allows the generation of a great mount of conductive paths at low pressure. The synergetic effects of inner space closure, pore collapse, and PPy NFs contact contributed to an ultra-high sensitivity of 0.8251 kPa−1, which surpasses reported foam-based sensors. The developed NOC foam possesses fast response time and recovery time (120 ms and 100 ms), high linearity, and excellent stability. Moreover, the sensor can be used to precisely detect the human walking, running, and jumping behaviors, and the grabbing force. When integrated into a sensing array, the NOC PPP foams demonstrated excellent potential to be used in human activity monitoring such as yoga postures and sleeping positions. This work provides new thoughts for designing biomimetic highly sensitive piezoresistive sensors and enhancing the foam stability using PPy NFs. [ABSTRACT FROM AUTHOR]

• Enhanced piezoresistive performance of piezoresistive sensor was achieved with the assistance of brittle CNC. • The existence of amphiphilic CNC is beneficial for the dispersion of CNT and the improved compression properties. • The flexible piezoresistive sensor could be applied for human motion detection and artificial electronic skin. Recently, piezoresistive sensors with wide response range and high sensitivity are in great demands with the rapid development of flexible electronic industry. To meet the demands, highly compressible waterborne polyurethane (WPU)/carbon nanotube (CNT) composite foam with enhanced piezoresistive performance was designed through incorporating the brittle cellulose nanocrystal (CNC) during the fabrication process. Here, the homogeneous dispersion of CNT with the assistance of amphiphilic CNC and the good interfacial interaction between CNC and TPU endowed the composite foam with improved compression properties. In addition, the brittle CNC/CNT conductive network is easier to be destructed, generating more significant resistance variation and about as high as 2.5 times the sensitivity of composite foam without CNC. As a piezoresistive sensor, it exhibits good compressibility and stable piezoresistive sensing signal in 80% compression strain range due to the porous structure and good elasticity of WPU. Cyclic piezoresistive sensing tests under different compression strains and rates demonstrate the excellent recoverability and reproducibility of the piezoresistive sensor after the initial stabilization process. More importantly, it also displays a fast response time of about 30 ms and good durability and reproductivity over 1000 compression cycles. Finally, the piezoresistive sensor can be successfully applied to detect various human motions (such as vocal cords/cheeks/fingers/wrists/feet movements) and to fabricate artificial electronic skin. The investigation provides an effective strategy for the fabrication of high-performance piezoresistive sensor. [ABSTRACT FROM AUTHOR]

• A flexible CB/TPU foam with a pinnate-veined aligned porous structure was prepared. • The foam can both serve as a flexible strain sensor and an adsorption material. • The foam sensor has excellent sensing discernibility and high sensitivity. • The sensor exhibits superior response stability in a wide sensing range. In this paper, flexible conductive carbon black (CB)/thermoplastic polyurethane (TPU) foam (CTF) with an intriguing pinnate-veined aligned porous structure was fabricated via a unidirectional freeze-drying process. The density, porosity and average pore size of the composite foam are 0.13 g cm−3, 83.7% and 24.9 μm, respectively. CB particles are uniformly dispersed in the skeleton of the as-prepared foam, resulting in a low percolation threshold of 0.48 vol%. The CTF is capable of distinguishing different compressive strain by change of the relative resistance. Its responsive behaviors towards compressive strain present an excellent linear characteristic with a high gauge factor (GF) up to 1.55. In the piezoresistive tests, the CTF shows a fast response/relaxation time (150/150 ms), fascinating recoverability, excellent response stability within a wide workable detection range up to 80% strain (corresponding pressure of 584.4 kPa) and a superior durability (>10000 cycles), which is mainly related to the pinnate-veined aligned porous structure along the orientation direction. The CTF was then assembled as a wearable sensor to monitor various human motions such as arm bending, squatting, tiptoeing, etc., showing good detection performances. The sensor can also deal with water pollution through oil/water separation, suggesting its multifunctionality and promising prospects in complicated situations. [ABSTRACT FROM AUTHOR]