Display form factors such as size and shape have been conventionally determined in consideration of usability and portability. The recent trends requiring wearability and convergence of various smart ...devices demand innovations in display form factors to realize deformability and large screens. Expandable displays that are foldable, multi-foldable, slidable, or rollable have been commercialized or on the edge of product launches. Beyond such two-dimensional (2D) expansion of displays, efforts have been made to develop three dimensional (3D) free-form displays that can be stretched and crumpled for use in realistic tactile sensation, artificial skin for robots, and on-skin or implantable displays. This review article analyzes the current state of the 2D and 3D deformable displays and discusses the technological challenges to be achieved for industrial commercialization.
Human cutaneous tactile receptors are deformable, and can distinguish touch, strain, relative moving distance, and relative moving velocity. In addition, the tactile potential is self-activated when ...external stimulation is exerted and the potential is transmitted to the nerve system, resembling the wake-up function in electronic devices. In this study, we mimic such characteristics of the human tactile receptors. We designed a stretchable triboelectric nanogenerator (TENG) for the stimuli-responsive potential generator. The TENG device has a multilayer structure independently recognizing lateral strain by the sliding mode, touch by the contact mode, the relative moving distance, and the relative moving velocity. In addition, the device design allows simultaneous sensing of strain and touch without signal interference. The self-triggered potentials generated by various body motions such as touching, joint bending, and the combinations turn on a sleeping microcontroller unit (MCU) and are used as the distinct motion signals. This study demonstrates a wearable low-power remote tactile interface that controls the 3D movements of a mobile device (drone) by the body motions.
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•The TENG sensor can distinguish pressure, strain, distance, velocity.•The sensor can extract information from random dynamic motions.•The integrated wearable haptic interface can control complex 3-D movement of a drone.•The wake-up function is turned on or off by the sensor signal itself.
In this work, we developed highly flexible transparent film heaters (f-TFHs) composed of Ag nanowire networks (AgNWs) and aluminum zinc oxide (AZO). Uniform AgNWs were roll-to-roll coated on ...polyethylene terephthalate (PET) substrates using the Mayer rod method, and AZO was sputter-deposited atop the AgNWs at room temperature. The sheet resistance (R s) and transparency (T opt) of the AZO-coated AgNWs changed only slightly compared with the uncoated AgNWs. AZO is thermally less conductive than the heat pipes, but increases the thermal efficiency of the heaters blocking the heat convection through the air. Based on Joule heating, a higher average film temperature (T ave) is attained at a fixed electric potential drop between electrodes () as the R s of the film decreases. Our experimental results revealed that T ave of the hybrid f-TFH is higher than AgNWs when the ratio of the area coverage of AgNWs to AZO is over a certain value. When a as low as 3V/cm was applied to 5cm5cm f-TFHs, the maximum temperature of the hybrid film was over 100 degree C, which is greater than that of AgNWs by more than 30 degree C. Furthermore, uniform heating throughout the surfaces is achieved in the hybrid films while heating begins in small areas where densities of the nanowires (NWs) are the highest in the bare network. The non-uniform heating decreases the lifetime of f-TFHs by forming hot spots. Cyclic bending test results indicated that the hybrid films were as flexible as the AgNWs, and the R s of the hybrid films changes only slightly until 5000cycles. Combined with the high-throughput coating technology presented here, the hybrid films will provide a robust and scalable strategy for large-area f-TFHs with highly enhanced performance.
Soft ionic sensors have emerged as a promising device form to accommodate various future electronic applications. One of the hurdles in ionic sensors is that the sensing signals by mechanical ...deformation and other stimuli are mixed up. Although the performance of the ionic sensors is highly dependent on the structure of electrodes, systematic investigation of purposive electrode design has been rarely explored. This study proposes a simple strategy for designing stretchable composite electrodes which make the ionic sensor strain‐negative, strain‐neutral, and strain‐positive. This study reveals that such strain‐responses can be obtained by adjusting the surface coverage of the electrically‐effective conductive fillers. On the basis of the concept, deposition of a Au film on an elastomer composite and crack formation of the Au film are presented for the practical fabrication of a highly reproducible strain‐neutral ionic sensor. A completely strain‐independent temperature sensor is demonstrated by using the Au crack‐based ionic sensor. In addition, this study demonstrates a two‐terminal shear sensor capable of recognizing shear directions by combining the strain‐positive and strain‐negative electrodes.
This work investigates the influence of the electrically‐effective surface area of the composite electrode on the strain responses in the ion‐gel tactile sensors. It demonstrates facile designs of the composite electrodes to obtain strain‐negative, strain‐neutral, and strain‐positive impedance responses to external stretching.
Buckling patterns of polymer thin films on plasma-treated poly(dimethylsiloxane) (PDMS) substrates were sensitively affected by the thickness of the substrate in addition to the substrate modulus. On ...highly crosslinked PDMS substrates, the buckling wavelength of polymer thin films sharply increased as the thickness of the substrates were raised and approached a plateau value when the substrate was 2.5 mm-thick. On weakly crosslinked PDMS substrates, the wavelength still increased even when the substrate was thicker than 20 mm. The high dependence of the buckling on the substrate thickness has not been reported before and is unexpected from the current predictions.
Well-defined ordered arrays of plasmonic nanostructures were fabricated on stretchable substrates and tunable plasmon-coupling-based sensing properties were comprehensively demonstrated upon ...extension and contraction. Regular nanoprism patterns consisting of Ag, Au and Ag/Au bilayers were constructed on the stretchable polydimethylsiloxane substrate. The nanoprisms had the same orientation over the entire substrate (3 × 3 cm
) via metal deposition on a single-crystal microparticle monolayer assembly. The plasmonic sensor based on the Ag/Au bilayer showed a 6-fold enhanced surface enhanced Raman scattering signal under 20% uniaxial extension, whereas a 3-fold increase was observed upon 6% contraction, compared with the Au nanoprism arrays. The sensory behaviors were corroborated by finite-difference time-domain simulation, demonstrating the tunable electromagnetic field enhancement effect via the localized surface plasmon resonance coupling. The advanced flexible plasmonic-coupling-based devices with tunable and quantifiable performance herein suggested are expected to unlock promising potential in practical bio-sensing, biotechnological applications and optical devices.
Abstract Deformable and miniaturized energy storage devices are essential for powering soft electronics. Herein, we fabricate deformable micro supercapacitors (MSCs) based on eutectic gallium-indium ...liquid metal (EGaIn) current collectors with integrated graphene. The well-define interdigitated electrode patterning with controlled gap is successfully realized by using the laser ablation because of a strong laser absorption of graphene and EGaIn. By judicious control of gap size between neighboring interdigitated electrodes and mass loading of graphene, we achieve a high areal capacitance (1336 µF cm −2 ) with reliable rate performance. In addition, owing to the intrinsic liquid characteristics of EGaIn current collector, the areal capacitance of fabricated MSC retains 90% of original value even after repetitive folding and 20% stretching up to 1000 cycles. Finally, we successfully integrate deformable MSC with a commercial light-emitting diode to demonstrate the feasibility of MSC as a deformable power source. The fabricated MSCs operate stably under various mechanical deformations, including stretching, folding, twisting, and wrinkling.
This study demonstrates the growth of long triisopropylsilyethynyl pentacene (TIPS‐PEN) nanofibrils in a thin film of a crystalline polymer, poly(ε‐caprolactone) (PCL). During spin‐coating, TIPS‐PEN ...molecules are locally extracted around the PCL grain boundaries and they crystallize into 010 direction forming long nanofibrils. Molecular weight of PCL and weight fraction (α) of TIPS‐PEN in PCL matrix are key factors to the growth of nanofibrils. Long high‐quality TIPS‐PEN nanofibrils are obtained with high‐molecular‐weight PCL and at the α values in the range of 0.03–0.1. The long nanofibrils are used as an active layer in a field‐effect organic transistor.
Long (>30 μm) TIPS‐PEN nanofibrils are generated in a thin film of crystalline polymer, poly(ε‐caprolactone), during spin‐coating. The long nanofibrils are used as an active layer of a field‐effect organic transistor.
Spherical polymeric core−shell microcapsules in uniform size were produced by electrospraying with a coaxial nozzle setup. Contrary to the usual coaxial setup, the inner nozzle was slightly bent to ...touch the inside wall of the outer nozzle. A polymer solution for the core was introduced through the outer nozzle, and the other solution for the shell was supplied through the inner nozzle. The setup greatly increased reproduction of the same results. As a proof of the concept, core−shell microcapsules consisting of a PS or PMMA core and a PCL shell (PS@PCL, PMMA@PCL) were produced. When the volumetric feed rate of the shell-forming PCL solution was higher than that of the core-forming PS or PMMA solution the core−shell structures in uniform size were readily obtained. In contrast, irregular morphologies were observed when the feed rate of the PCL solution was slower or equal to that of the PS or PMMA solution. The size of the colloid was dependent on the relative feed ratio between the polymer solutions as well as the magnitude of applied voltage.
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