A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of single‐walled carbon nanotube thin‐film transistors is demonstrated. The integrated temperature sensor ...array gives mechanical stability under biaxial stretching of 30%, and the resultant spatial temperature mapping does not show any mechanical or electrical degradation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The facile fabrication of thin and foldable self‐healing electronics on a poly(vinyl alcohol)/cellulose nanocrystal (PVA/CNC) composite film is reported. The self‐healing property of the PVA/CNC ...nanocomposite film can be activated by spraying water on the film surface, via dynamic formation of hydrogen bonding. The self‐healing efficiency of PVA/CNC is influenced by the content of CNC in the film, pH of the spraying solution, and the temperature. Via vacuum filtration and pattern transfer techniques, both a supercapacitor and a temperature sensor are fabricated on the same PVA/CNC film using gold nanosheet (AuNS) and polyaniline/multiwalled nanotube (PANI/MWCNT) electrodes. The fabricated supercapacitor with a gel‐type electrolyte exhibits a high electrochemical performance, and the thermoresistive temperature sensor shows a linear sensitivity with a fast response. Both devices exhibit superior mechanical stability and self‐healing property over 100 repetitive folding and five repetitive healing cycles, respectively, retaining the device performance owing to the percolated network of the conductive materials. This work demonstrates that our paper‐like thin PVA/CNC film‐based self‐healable devices can serve as highly durable and deformable electronics with longevity.
A paper‐like, thin, foldable, and self‐healable electronic based on poly(vinyl alcohol)/cellulose nanocrystal (PVA/CNC) nanocomposite film shows a water‐stimulated self‐healing property due to dynamic hydrogen bonding formation. A high‐performance planar supercapacitor and thermoresistive temperature sensor fabricated on the PVA/CNC substrate exhibits a high electrical self‐healing property after complete bisection as well as high mechanical stability under repetitive folding deformation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This study reports on the fabrication of pressure/temperature/strain sensors and all‐solid‐state flexible supercapacitors using only polydimethylsiloxane coated microporous polypyrrole/graphene foam ...composite (PDMS/PPy/GF) as a common material. A dual‐mode sensor is designed with PDMS/PPy/GF, which measures pressure and temperature with the changes of current and voltage, respectively, without interference to each other. The fabricated dual‐mode sensor shows high sensitivity, fast response/recovery, and high durability during 10 000 cycles of pressure loading. The pressure is estimated using the thermoelectric voltage induced by simultaneous increase in temperature caused by a finger touch on the sensor. Additionally, a resistor‐type strain sensor fabricated using the same PDMS/PPy/GF could detect the strain up to 50%. Flexible, high performance supercapacitor used as a power supply is fabricated with electrodes of PPy/GF for its high surface area and pseudocapacitance. Furthermore, an integrated system of such fabricated multifunctional sensors and a supercapacitor on a skin‐attachable flexible substrate using liquid–metal interconnections operates well, whereas sensors are driven by the power of the supercapacitor. This study clearly demonstrates that the appropriate choice of a single functional material enables fabrication of active multifunctional sensors for pressure, temperature, and strain, as well as the supercapacitor, that could be used in wirelessly powered wearable devices.
High‐performance solid‐state supercapacitors and multifunctional sensors sensitive to pressure, temperature, and strain are fabricated using a single common active material of microporous polydimethylsiloxane coated microporous polypyrrole/graphene foam composite. Furthermore, these sensors could be wirelessly driven with the integrated supercapacitors on a single flexible and skin‐attachable substrate.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this work, the authors report materials, fabrication strategies, and applications of biodegradable microsupercapacitors (MSCs) built using water‐soluble (i.e., physically transient) metal (W, Fe, ...and Mo) electrodes, a biopolymer, hydrogel electrolyte (agarose gel), and a biodegradable poly(lactic‐co‐glycolic acid) substrate, encapsulated with polyanhydride. During repetitive charge/discharge cycles, the electrochemical performance of these unusual MSCs is dramatically enhanced, following from the role of pseudocapacitance that originates from metal‐oxide coatings generated by electrochemical corrosion at the interface between the water‐soluble metal electrode and the hydrogel electrolyte. Systematic studies reveal the dissolution kinetics/behaviors of each individual component of the MSCs, as well as those of the integrated devices. An encapsulation strategy that involves control over the thickness, chemistry, and molecular weight of the constituent materials provides a versatile means to engineer desired functional lifetimes. Demonstration experiments illustrate potential applications of these biodegradable MSCs as transient sources of power in the operation of light‐emitting diodes and as charging capacitors in integrated circuits for wireless power harvesting.
An entirely biodegradable microsupercapacitor is successfully fabricated using water‐soluble metal electrodes, agarose gel electrolyte, and poly(lactic‐co‐glycolic acid) substrate. The development of biodegradable, high performance supercapacitors represents an important advance in the area of transient electronics, with potentially important consequences in technologies for biomedicine, environmental monitoring, sustainable electronics, and other areas.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is ...fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.
A highly stretchable and sensitive strain sensor based on a composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS) is fabricated in a facile process. The FGF/PDMS sensor demonstrates high stretchability up to 70% and high durability over 10 000 stretching cycles with gauge factor in the range of 15–29 depending on the maximum strain applied and the FGF content.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
As part of increased efforts to develop wearable healthcare devices for monitoring and managing physiological and metabolic information, stretchable electrochemical sweat sensors have been ...investigated. In this study, we report on the fabrication of a stretchable and skin-attachable electrochemical sensor for detecting glucose and pH in sweat. A patterned stretchable electrode was fabricated via layer-by-layer deposition of carbon nanotubes (CNTs) on top of patterned Au nanosheets (AuNS) prepared by filtration onto stretchable substrate. For the detection of glucose and pH, CoWO4/CNT and polyaniline/CNT nanocomposites were coated onto the CNT–AuNS electrodes, respectively. A reference electrode was prepared via chlorination of silver nanowires. Encapsulation of the stretchable sensor with sticky silbione led to a skin-attachable sweat sensor. Our sensor showed high performance with sensitivities of 10.89 μA mM–1 cm–2 and 71.44 mV pH–1 for glucose and pH, respectively, with mechanical stability up to 30% stretching and air stability for 10 days. The sensor also showed good adhesion even to wet skin, allowing the detection of glucose and pH in sweat from running while being attached onto the skin. This work suggests the application of our stretchable and skin-attachable electrochemical sensor to health management as a high-performance healthcare wearable device.
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IJS, KILJ, NUK, PNG, UL, UM
We report on the facile fabrication of a stretchable array of highly sensitive pressure sensors. The proposed pressure sensor consists of the top layer of Au-deposited polydimethylsiloxane (PDMS) ...micropillars and the bottom layer of conductive polyaniline nanofibers on a polyethylene terephthalate substrate. The sensors are operated by the changes in contact resistance between Au-coated micropillars and polyaniline according to the varying pressure. The fabricated pressure sensor exhibits a sensitivity of 2.0 kPa–1 in the pressure range below 0.22 kPa, a low detection limit of 15 Pa, a fast response time of 50 ms, and high stability over 10000 cycles of pressure loading/unloading with a low operating voltage of 1.0 V. The sensor is also capable of noninvasively detecting human-pulse waveforms from carotid and radial artery. A 5 × 5 array of the pressure sensors on the deformable substrate, which consists of PDMS islands for sensors and the mixed thin film of PDMS and Ecoflex with embedded liquid metal interconnections, shows stable sensing of pressure under biaxial stretching by 15%. The strain distribution obtained by the finite element method confirms that the maximum strain applied to the pressure sensor in the strain-suppressed region is less than 0.04% under a 15% biaxial strain of the unit module. This work demonstrates the potential application of our proposed stretchable pressure sensor array for wearable and artificial electronic skin devices.
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IJS, KILJ, NUK, PNG, UL, UM
The fabrication of a skin‐attachable, stretchable array of high‐sensitivity temperature sensors is demonstrated. The temperature sensor consists of a single‐walled carbon nanotube field‐effect ...transistor with a suspended gate electrode of poly(N‐isopropylacrylamide) (PNIPAM)‐coated gold grid/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate and thermochromic leuco dye. The sensor exhibits a very high sensitivity of 6.5% °C−1 at temperatures between 25 and 45 °C. With increasing temperature, the suspended gate electrode bends due to the deswelling of the PNIPAM, resulting in the reduction of the air gap to increase the drain current under a constant gate voltage. At the same time, the leuco dye coated on top of the transparent gate electrode changes color to visualize changes in temperature. The 4 × 6 integrated temperature sensor array integrated using liquid metal interconnections exhibits mechanical and electrical stability under 50% biaxial stretching and allows for the spatial mapping of temperature with visual color display regardless of wrist movement while attached to the skin of the wrist. This work is expected to be widely useful in the development of skin‐attachable electronics for medical and health‐care monitoring.
A high‐sensitivity, skin‐attachable, and stretchable 4 × 6 temperature sensor array of single‐walled carbon nanotube field‐effect transistors with a thermo‐responsive suspended gate and thermochromic display is demonstrated. The integrated temperature sensor array with a high sensitivity of 6.5% °C−1 provides mechanical stability, resulting in no mechanical or electrical degradation under biaxial stretching and wrist movement while attached to the skin of the wrist.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We report a fabrication of a high-performance wire-type supercapacitor through surface modification of carbon fiber with ionic liquid, nanomaterials, and gel electrolyte containing ionic liquid. ...Coating of Au nanoparticles onto carbon fiber increases both surface area and electrical conductivity. Dip-coating of mixture of ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI), carbon nanotubes, and electropolymerization of polypyrrole (Ppy) onto Au coated fiber for pseudocapacitance results in high capacitance. The use of propylene carbonate-poly(methyl methacrylate)-EMIMTFSI gel electrolyte gives high operation voltage. Such wire-type supercapacitor exhibits a high voltage of 2.5 V, an areal capacitance of 38.49 mF cm−2, and a maximum energy and power density of 24.7 μWh cm−2 and 3.52 mW cm−2, respectively. In addition, the cyclic stability of the supercapacitor is dramatically enhanced by using 2-naphthalene sulfonic acid as a dopant in electropolymerization of Ppy. Encapsulation with a thermally shrinkable tube endows the supercapacitor with mechanical stability and waterproof features when it is bent, folded, twisted, even in water. This work demonstrates high potential of such wire-type supercapacitor as a flexible energy-storage device for various applications, especially those that require high voltage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A high‐voltage supercapacitor with shape memory for driving an integrated NO2 gas sensor is fabricated using a Norland Optical Adhesive 63 polymer substrate, which can recover the original shape ...after deformation by short‐time heating. The supercapacitor consists of multiwalled carbon nanotube electrodes and organic electrolyte. By using organic electrolyte consisting of adiponitrile, acetonitrile, and dimethyl carbonate in an optimized volume ratio of 1:1:1, a high operation voltage of 2 V is obtained. Furthermore, asymmetric electrolytes with different redox additives of hydroquinone and 1,4‐dihydroxyanthraquinone to the anode and cathode, respectively, enhance both capacitance and energy density by ≈40 times compared to those of supercapacitor without redox additives. The fabricated supercapacitor on the Norland Optical Adhesive 63 polymer substrate retains 95.8% of its initial capacitance after 1000 repetitive bending cycles at a bending radius of 3.8 mm. Furthermore, the folded supercapacitor recovers its shape upon heating at 70 °C for 20 s. In addition, 90% of the initial capacitance is retained even after the 20th shape recovery from folding. The fabricated supercapacitor is used to drive integrated NO2 gas sensor on the same Norland Optical Adhesive 63 substrate attached onto skin to detect NO2 gas, regardless of deformation due to elbow movement.
The fabrication of a shape memory high‐voltage supercapacitor with asymmetric nonaqueous electrolytes including redox additives for driving an integrated NO2 gas sensor is demonstrated. Using an asymmetric organic electrolyte greatly enhances the performance of the supercapacitor. Furthermore, the supercapacitor and NO2 gas sensor can be driven after several shape recoveries, successfully.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
