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•Low-pressure-oxygen plasma was introduced to the preparation of conductive foams.•Skeleton of plasma-treated foams have better affinity with conductive layer.•The as-prepared foams ...exhibit excellent compressive sensitivity and durability.
Rapid development of artificial intelligence and wearable electronics facilitate the demand for high performance piezoresistive sensors. Not only high sensitivity but also good mechanical property as well as long-term usage are critical parameters to value piezoresistive sensors performance. In this work, a flexible, highly sensitive and versatile piezoresistive sensor with 3D porous structures, based on commercially available polyurethane (PU) foams coated with cellulose nanofiber @ carbon black (CNF@CB) conductive layer, was fabricated. We are particularly interested in the effect of interaction between the conductive filler and PU foam on the sensor performance. Thus, low-pressure oxygen plasma treatment was innovatively adopted to modify and activate PU scaffold to enhance the affinity between PU framework and CNF@CB conductive layer. Strong interfacial interaction is not only contributed to the sensitivity but also to the mechanical reinforcement of conductive foams, which is helpful to the long-term usage. The as-prepared PU/CNF@CB conductive foams exhibit very high compressive sensitivity of 0.35 kPa−1 (about 100% increase compared with the untreated ones), along with good mechanical property (29 kPa at 50% compressive strain, about 27% increase compared with the untreated ones) and electrical property (0.047 S/m). In addition, good stability and durability are demonstrated for the prepared PU/CNF@CB conductive foams especially under micro-pressure or micro-strain which is a huge challenge for bulk piezoresistive sensors. Such a kind of sensitive material combined with low-cost, flexibility, high sensitivity, duration, is very attractive in high-tech area.
•Fabrication of 3D graphene-based wearable piezoresistive sensors are summarized.•Mechanism and application of 3D graphene-based piezoresistive sensors are combed.•Challenge and prospect of 3D ...graphene-based piezoresistive sensors are discussed.
Three-dimensional (3D) graphene based wearable piezoresistive sensors are considered as promising flexible sensors due to their facile preparation, simple read-out mechanism, low power consumption and convenient signal acquisition. After nearly two decades of rapid development, 3D graphene based piezoresistive sensors have shown excellent application potential in human motion detection, heath monitoring, electronic skin, etc., which are envisioned as the critical technologies in future artificial intelligence system. In this review, the rapid development of 3D graphene based piezoresistive sensors are focused and analyzed. Various preparation methods of graphene and the complex fabrication process of multilevel 3D graphene structure are summarized, followed by the analyzing of different working mechanisms of 3D graphene-based piezoresistive sensors, which are illustrated by examples. The challenges and prospects of 3D graphene-based piezoresistive pressure sensors are discussed.
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Flexible pressure sensors still face a great challenge to combine fast frequency response, wide pressure range, multiple detection modes, satisfactory mechanical and environmental ...stability, and simple fabrication process into a sensor. Herein, flexible piezoresistive pressure sensors are fabricated by treating the backbone of polyurethane (PU) sponge with chitosan (CS) to obtain positively charged CS@PU sponge, followed by dip-coating of negatively charged Ti3C2Tx MXene sheets. The resulting MXene@CS@PU sponge-based sensor provides a versatile sensing platform with potentials for detecting both small and large pressure signals. Due to the highly compressive resilience of the PU sponge and its polar interaction with the MXene sheets, the MXene@CS@PU sensor has high compressibility and stable piezoresistive response for compressive strains of up to 85% with a stress of 245.7 kPa, and it also exhibits a satisfactory reproducibility for 5000 compression-release cycles. Even after washing in water for 1 h, the sensor still shows good performances. With a rapid response time of only 19 ms and a low detection limit of 30 μN corresponding to a pressure of 9 Pa, the MXene sponge sensor is promising for detecting human physiological signals and insect movements. In addition to the contact mode detection, the sponge sensor could detect voices and human breaths by a non-contact detection mode.
•Flexible and compressible conductive hybrid aerogels of PEDOT:PSS/PI were fabricated.•The hybrid displayed well-ordered “layer-strut” porous structure linked with fibrils.•The hybrid aerogel ...exhibited stable and linearly piezoresistive responses.•It retained good compressive sensitivity and durable stability in severe environments.
The construction of flexible all-polymer-based conductive aerogels for piezoresistive pressure sensors is often hindered by a trade-off between robust mechanical properties and elastic-responsive conductivity. Here, a highly flexible and compressible conductive aerogel was fabricated by integrating poly(3,4-thylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with polyimide (PI) through facile strategies of freeze-drying and thermal annealing. With a controlled ratio of the two components, the composite demonstrates a well-ordered and interconnected porous structure composed of “layer-strut” skeletons with linked fibrils. Benefiting from the unique structure and synergistic effects between the two polymers, the PEDOT:PSS/PI aerogel exhibits excellent compressibility, stable and linear piezoresistive responses at various compressive strains and good reproducibility over 200 cycles. Furthermore, the hybrid can retain good compression sensitivity and durable stability in severe environments, such as at high and low temperatures and under acidic conditions, demonstrating its great potential for a wide range of pressure sensor applications in harsh environments.
•Novel manufacturing method was introduced to disperse nano fillers.•Piezoresistive sensing characteristics of the composites were observed.•Incorporation of CIP into the composites improved sensing ...capabilities.
The electrical and piezoresistive sensing characteristics of polymeric composites incorporating carbon nanotube (CNT) and carbonyl iron powder (CIP) were investigated in this study. A novel manufacturing method was introduced to effectively and uniformly disperse CNT and CIP into polymeric composites. Five different CNT proportions and three different CIP proportions were considered to explore the synergistic effects of CNT and CIP incorporation on the electrical and the piezoresistive sensing characteristics of the composites. Piezoresistive sensing characteristics (e.g., electrical resistance changes, time-based peak shifts, R-square values) of the composites were observed, and the effect of the magnetization on their piezoresistive sensing characteristics was also examined. The incorporation of CIP into CNT-embedded polymeric composites was shown to improve the piezoresistive sensing characteristics of the polymeric composites under cyclic tensile strain loads.
•An ultrasensitive bionic sensor was rationally designed and realized.•The flexible bionic sensor was fabricated by molding and spraying methods.•A layer of PVA fiber was fabricated by the ...electrospinning method to further enhance the sensitivity of the bionic sensor.•The bionic sensor displays ultrahigh sensitivity of 403.46 kPa−1.•The bionic sensor possesses great potential applications in physiological signal test field.
An ultrasensitive bionic MXene based piezoresistive pressure sensor was rationally designed and realized by molding the microstructure of the ginkgo leaf. Specifically, the core deformation part of the sensor under the applied force has been fabricated by imprinting the array-like microscopic shapes of the ginkgo leaves. The MXene-based pressure sensor was prepared by spraying the MXene onto the polydimethylsiloxane (PDMS) model film with the ginkgo leaf structure. To further enhance the sensitivity, a layer of polyvinyl alcohol (PVA) fiber fabricated by the electrospinning method was weaved between the MXene-based element and the electrodes in the sensor. Then, the obtained pressure sensor demonstrated ultrahigh sensitivity of 403.46 kPa−1, short response time of 99.3 ms and extraordinary durability with 12,000 loading–unloading cycles. Furthermore, the microstructure change of the sensor under applied pressure was observed through the in-situ scanning electron microscope (SEM) experiment. Meanwhile, the pressure sensor also displays great potential applications ranging from the physiological signal test to the human–computer interaction field.
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•Simple and effective MXene-based composite aerogel preparation method.•Excellent mechanical property and compressive strength is up to 16 kPa.•Sensitivity can as high as 114.55 kPa−1 ...in the wide pressure range up to 21.78 kPa.•Durability of the sensor can withstand more than 24,000 cycles of compression.•High-performance wearable pressure sensor for wireless signal transmission.
The emerging wearable electronics promote the rapid development of flexible piezoresistive sensors. However, it remains a big challenge to develop a high-performance piezoresistive sensor with high sensitivity, wide pressure range, and stable output. Here, an lightweight (17.33 mg cm−3) cellulose acetate nanofiber/sodium alginate synergistically enhanced MXene composite aerogel is fabricated through a liquid nitrogen-assisted unidirectional-freezing strategy. The conductive MXene-based aerogel possesses excellent mechanical performance and high compressive strength (16 kPa). Importantly, the unique synergies endow the aerogel assembled piezoresistive sensor with an ultra-high sensitivity up to 114.55 kPa−1 in a wide pressure range up to 21.78 kPa, and it can withstand more than 24,000 cycles of compression. More interestingly, the prepared sensor can be used to realize real-time monitoring of various human activities and developed as a wireless device to transmit information. The unparalleled sensing performance endows the MXene composite aerogel with a broad application prospect in the field of flexible intelligent wearable devices.
•Development of a theoretical analysis model by considering pore wall deformation, pore closure, and pore wall cracking.•Mechanism of negative piezoresistivity at low porosity and positive ...piezoresistivity at high porosity.•Explanation of high rebound resistance by considering pore wall deformation, pore closure, and pore wall cracking.•Establishment of OC model based on densely packed structures for piezoresistive mechanism under small deformations.
Piezoresistive porous elastomers (PPEs) are gaining attention in the field of flexible electronics due to their unique properties including ultra softness, ultra lightness, and high sensitivity. These properties can be precisely adjusted through advanced material synthesis and micro/nanofabrication technologies that control the size, shape, and composition of the functional nanoparticles. Despite various theoretical models of porous materials developed to advance the design of these materials, issues such as reverse piezoresistive response and resistance overshooting remains to be unsolved. Using principles of elastic mechanics and electrical tunnel effects, the present study introduces an analytical model that considers the effects of multimodal buckling of the pore wall, pore closure, microcracks, and mismatch within the pore wall under large deformation. The proposed model achieves a 99.5 % accuracy rate in describing the piezoresistive response (stress and resistance) under 75 % compression deformation by incorporating electrical tunnel theory into the mechanical model. The study also uncovers the mechanism behind high resistance overshooting and its relevant influences, including factors such as loading speed and application temperature. These findings are expected to drive the development of better porous composites and pave the way for practical applications of PPEs in various fields of smart sensors.
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•F-rGO@CNTs/CS aerogel was simply prepared by freeze-drying and dip-coating.•F-rGO@CNTs/CS aerogel possessed superhydrophobicity, compressibility and resilience.•F-rGO@CNTs/CS aerogel ...based sensor showed high sensitivity, fast response and good repeatability.•The sensor was successfully applied for detecting human motions even under wet environment.
Piezoresistive pressure sensors with high sensitivity, fast response, and simplified signal collection play an important role in a wide variety of fields. However, most of them are water-sensitive and easily attacked by water, leading to serious signal distortion in practical application. Herein, we fabricated a conductive and superhydrophobic 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS) modified reduced graphene oxide@carbon nanotubes/chitosan (F-rGO@CNTs/CS) aerogel for piezoresistive pressure sensor. Benefiting from the porous structure of aerogel and the synergy of CNTs and rGO, the aerogel sensor achieved high sensitivity and fast response. Moreover, the sensor maintained a stable electrical resistance response after 1000 loading-unloading cycles. Importantly, owing to the rough structure constructed by CNTs and multi-pores and the low surface energy of FAS, the sensor possessed superhydrophobic property with a high water contact angle of 154°, and exhibited remarkable water repellency even during compression process. In addition, the sensor was successfully applied for detecting human behaviors from small-scale muscle movements to large-scale body motions. Our findings provide a new direction to fabricate functional and high-performance piezoresistive pressure sensor for various applications even under water or wet environment.
