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The microstructural changes caused by the addition of the ionic liquid (IL) 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide to polydimethylsiloxane (PDMS) elastomer composites filled with carbon black (CB) are analyzed to explain the electrical, mechanical, rheological, and optical properties of IL‐containing precursors and composites. Swelling experiments and optical analysis indicate a limited solubility of the IL in the PDMS matrix that reduces the cross‐linking density of PDMS both globally and locally, which reduces the Young's moduli of the composites. A rheological analysis of the precursor mixture shows that the IL reduces the strength of carbon–carbon and carbon–PDMS interactions, thus lowering the filler–matrix coupling and increasing the elongation at break. Electromechanical testing reveals a combination of reversible and irreversible piezoresistive responses that is consistent with the presence of IL at microscopic carbon–carbon interfaces, where it enables re‐established electrical connections after stress release but reduces the absolute conductivity. [ABSTRACT FROM AUTHOR]

For thermoplastic material extrusion 3D‐printing functional filaments with electrically conductive, piezoresistive, piezoelectric, capacitive or magnetic properties are developed. The functional filaments result in piezoresisitve static/quasi‐static sensors; however, these 3D‐printed sensors are manufactured in several processes, for example, the creation of highly conductive paths using embedded copper wires or by silver inking. The multi‐process 3D printing of sensors presents an obstacle to smart functional 3D‐printed structures where the sensory element is in situ printed at the location and orientation of use, including the electrical paths. This research introduces a three axial piezoresistive accelerometer where the whole sensor, including highly conductive electrical paths, is printed in the same process of thermoplastic material extrusion. The structural components of the sensor are printed with a non‐conductive polylactide material, the sensory element with a conductive material that has a relatively high resistivity, and the electrical paths with a conductive material that has a relatively low resistivity. As discussed in the manuscript with single‐process sensors, the functional tuning of sensors is as easy as changing the design. The design and manufacturing solutions researched for the triaxial accelerometer can be applied to other 3D‐printed sensors, for example, force sensors and opens up the possibility of a single‐process 3D‐printed smart structure. [ABSTRACT FROM AUTHOR]

Stretchable and soft piezoresistive composites are appealing for application to tactile sensors, artificial skin, and wearable electronics. The ability of the composites to deform the geometries when they are strained can allow the electrical behavior of the composites to be manipulated. Although rigid metal and semiconductor inclusions have been utilized to create piezoresistive composites, they limit the degree of mechanical deformation. Here, liquid metal (gallium, melting point ≈ 29.7 °C) inclusion into elastomeric foam substrate with 3D open cell morphologies is utilized. Gallium is a fluidic conductor, thus it is possible to infiltrate the liquid metal into the 3D interconnected pore, resulting in soft, stretchable, and shape reconfigurable conductive composites that can change shape and function in response to external stimuli. Applying strain can enable deformation of the liquid metal, generating changes of electrical resistance. Interestingly, it is found that this piezoresistivity of the composite can be positively and negatively manipulated by adjusting the geometries of the liquid metal in the foam. Furthermore, the liquid metal in the elastomeric foam can be reversibly actuated by applying compressive force, resulting in manipulation of the restorative electrical activity of the composites. [ABSTRACT FROM AUTHOR]

Abstract: Flexible force sensors based on graphene/polymer nanocomposites have attracted tremendous attention owing to their remarkable sensitivity and ease of fabrication. In the present study, nanocomposites consisting of graphene as conducting fillers in a polyimide matrix are prepared, and an electrical breakdown method is used to endow the nanocomposite with a high piezoresistivity. Electromechanical tests and theoretical models confirm that the piezoresistivity of the nanocomposite originates from the cracks in the carbonized polymers induced by electrical breakdown. The fabricated force sensor exhibits a broad working range of 0–495 kPa, ultrafast response (2.12 ms), and excellent stability (>2000 compression–release cycles). In addition, the sensitivities of the force sensor can be tuned by varying the applied current in the electrical breakdown process. Thus, the electrical breakdown method allows highly facile fabrication of piezoresistive force sensors with tunable sensitivities. [ABSTRACT FROM AUTHOR]

The design and fabrication of various types of flexible, portable, and foldable devices have received immense interest owing to the remarkable potential in impacting peoples' lives including real‐time health monitoring, point‐of‐care diagnosis, and athletic training. In this work, the authors present 3D graphite as the key sensing element of polymer composite strain sensors that offers ultrahigh sensitivity and durability in the detection of fine motions. The graphite–polymer sensors in this work provide high bending sensitivities that are reproducible within 3% signal shift after 11 000 bending cycles and exhibit gauge factors of 100 and 52 at tensile strains of 80% and 100%, respectively. The sensing mechanism is modeled, and correlated with experimental studies. The high strain sensitivity compared to graphene based devices is analyzed and understood with respect to levels of defect in materials. Such graphite–polymer sensors are able to detect fine features of human pulses, respiration rates, and throat vibration in real time and are also applied in the detection of posture correctness of musical instrument learners for the first time. [ABSTRACT FROM AUTHOR]

Copper nanowires (CuNWs) are highly conductive yet low‐cost nanostructures for constructing piezoresistive pressure sensors. Rational design and controllable fabrication are essential steps toward high‐performance CuNW‐based sensors, and the oxidation tendency of CuNWs must be inhibited. Conducting and flexible CuNW@graphene (CuNW@G) core–shell aerogels are fabricated with tunable microstructures via a simple assembly followed by thermal annealing, in which the aerogel bulk density, surface wettability, Young's modulus, and electrical conductivity can be adjusted accordingly by varying the initial CuNW dispersion concentration. In particular, these core–shell aerogels convert from hydrophobic to superhydrophobic at higher CuNW concentration with reduced adhesion to water. In the range of investigated CuNW dispersion concentration, the chemical constituent and structure of as‐produced graphene shell is nearly the same, as is the aerogel's antioxidation stability. Based on the piezoresistivity of the core–shell aerogels, flexible pressure sensors operated at a bias voltage of 0.1 V are demonstrated, which can detect compressive stress as low as 640 Pa and exhibit fast response time less than 16 ms. Furthermore, polydimethylsiloxane‐encapsulated CuNW@G aerogels show an enhanced response and higher reversibility. A general and scalable strategy for developing aerogel‐typed piezoresistive pressure sensors with stable performance and low cost is presented. [ABSTRACT FROM AUTHOR]

Highly sensitive tactile sensors with long‐term stability and low power consumption are one of the key components for flexible electronics. Here, for the first time, the fabrication of VO2 nanomembrane tactile sensors by epitaxial liftoff from ZnO sacrificial layer is reported. The wafer‐scale nanomembranes inherit the structural and electrical properties of the as‐grown films, and the wet transfer generates negligible influence on the quality of VO2. Most importantly, giant electrical responses to external strains are found due to the release of substrate clamping, and a high gauge factor up to ≈1100 is derived. Furthermore, the electrical properties show no deterioration after repeatedly bending the nanomembranes for 10 000 times at a radius of 1 cm. The VO2 nanomembrane sensors are utilized to monitor the radial artery pulse, and totally reproducible waveforms with ultrahigh sensitivity to the tactile stimuli are observed. Moreover, the power dissipation of the VO2 tactile sensors can be lowered down to the picowatt level, allowing for the future construction of self‐powered sensing systems together with nanogenerators. This study provides a substantial step toward large‐scale preparation of oxide nanomembranes and therefore paves a promising way for flexible oxide electronics. [ABSTRACT FROM AUTHOR]

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