4 research outputs found
Biaxially Stretchable, Integrated Array of High Performance Microsupercapacitors
We report on the fabrication of a biaxially stretchable array of high performance microsupercapacitors (MSCs) on a deformable substrate. The deformable substrate is designed to suppress local strain applied to active devices by locally implanting pieces of stiff polyethylene terephthalate (PET) films within the soft elastomer of Ecoflex. A strain suppressed region is formed on the top surface of the deformable substrate, below which PET films are implanted. Active devices placed within this region can be isolated from the strain. Analysis of strain distribution by finite element method confirms that the maximum strain applied to MSC in the strain suppressed region is smaller than 0.02%, while that on the Ecoflex film is larger than 250% under both uniaxial strain of 70% and biaxial strain of 50%. The all-solid-state planar MSCs, fabricated with layer-by-layer deposited multiwalled carbon nanotube electrodes and patterned ionogel electrolyte of poly(ethylene glycol) diacrylate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide having high-potential windows, are dry-transferred onto the deformable substrate and electrically connected in series and parallel <i>via</i> embedded liquid metal interconnection and Ag nanowire contacts. Liquid metal interconnection, formed by injecting liquid metal into the microchannel embedded within the substrate, can endure severe strains and requires no additional encapsulation process. This formed MSC array exhibits high energy and power density of 25 mWh/cm<sup>3</sup> and 32 W/cm<sup>3</sup>, and stable electrochemical performance up to 100% uniaxial and 50% biaxial stretching. The high output voltage of the MSC array is used to light micro-light-emitting diode (μ-LED) arrays, even under strain conditions. This work demonstrates the potential application of our stretchable MSC arrays to wearable and bioimplantable electronics with a self-powered system
Stretchable Array of Highly Sensitive Pressure Sensors Consisting of Polyaniline Nanofibers and Au-Coated Polydimethylsiloxane Micropillars
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<sup>–1</sup> 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
Fabrication of High-Sensitivity Skin-Attachable Temperature Sensors with Bioinspired Microstructured Adhesive
In
this study, we demonstrate the fabrication of a highly sensitive flexible
temperature sensor with a bioinspired octopus-mimicking adhesive.
A resistor-type temperature sensor consisting of a composite of polyÂ(<i>N</i>-isopropylacrylamide) (pNIPAM)-temperature sensitive hydrogel,
polyÂ(3,4-ethylenedioxythiophene) polystyrene sulfonate, and carbon
nanotubes exhibits a very high thermal sensitivity of 2.6%·°C<sup>–1</sup> between 25 and 40 °C so that the change in skin
temperature of 0.5 °C can be accurately detected. At the same
time, the polydimethylsiloxane adhesive layer of octopus-mimicking
rim structure coated with pNIPAM is fabricated through the formation
of a single mold by utilizing undercut phenomenon in photolithography.
The fabricated sensor shows stable and reproducible detection of skin
temperature under repeated attachment/detachment cycles onto skin
without any skin irritation for a long time. This work suggests a
high potential application of our skin-attachable temperature sensor
to wearable devices for medical and health-care monitoring
Wire-Shaped Supercapacitors with Organic Electrolytes Fabricated via Layer-by-Layer Assembly
A wire-shaped supercapacitor
(WSS) has structural advantages of
high flexibility and ease of incorporation into conventional textile
substrates. In this work, we report a thin reproducible WSS fabricated
via layer-by-layer (LbL) assembly of multiwalled carbon nanotubes
(MWCNTs), combined with an organic electrolyte of propylene carbonate
(PC)–acetonitrile (ACN)–lithium perchlorate (LiClO<sub>4</sub>)–polyÂ(methyl methacrylate) (PMMA) that extends the
voltage window to 1.6 V. The MWCNTs were uniformly deposited on a
curved surface of a thin Au wire using an LbL assembly technique,
resulting in linearly increased areal capacitance of the fabricated
WSS. Vanadium oxide was coated on the LbL-assembled MWCNT electrode
to induce pseudocapacitance, hence enhancing the overall capacitance
of the fabricated WSS. Both the cyclic stability of the WSS and the
viscosity of the electrolyte could be optimized by controlling the
mixing ratio of PC to ACN. As a result, the fabricated WSS exhibits
an areal capacitance of 5.23 mF cm<sup>–2</sup> at 0.2 mA cm<sup>–2</sup>, an energy density of 1.86 μ W h cm<sup>–2</sup>, and a power density of 8.5 mW cm<sup>–2</sup>, in addition
to a high cyclic stability with a 94% capacitance retention after
10 000 galvanostatic charge–discharge cycles. This work
demonstrates a great potential of the fabricated scalable WSS in the
application to high-performance textile electronics as an integrated
energy storage device