Heterogeneous Configuration of a Ag Nanowire/Polymer Composite Structure for Selectively Stretchable Transparent Electrodes

One of the most important aspects that we need to consider in the design of intrinsically stretchable electrodes is that most electronic devices that can be formed on them are not stretchable themselves. This discrepancy can induce severe stress singularities at the interfaces between stiff devices and stretchable electrodes, leading to catastrophic device delamination when the substrate is stretched. Here, we suggest a novel solution to this challenge which involves introducing a photolithography-based rigid-island approach to fabricate the heterogeneous configuration of a silver nanowire (AgNW)/polymer composite structure. For this, we designed two new transparent polymers: a photopatternable polymer that is rigid yet flexible, and a stretchable polymer, both of which have identical acrylate functional groups. Patterning of the rigid polymer and subsequent overcoating of the soft polymer formed rigid island disks embedded in the soft polymer, resulting in a selectively stretchable transparent film. Strong covalent bonds instead of weak physical interactions between the polymers strengthened the cohesive force at the interface of the rigid/soft polymers. Inverted-layer processing with a percolated AgNW network was used to form a heterogeneous AgNW/polymer composite structure that can be used as a selectively stretchable transparent electrode. An optimized structural configuration prevented the resistance of the rigid electrode from varying up to a lateral strain of 70%. A repeated stretch/release test with 60% strain for 5000 cycles did not cause any severe damage to the structure, revealing that the fabricated structure was mechanically stable and reliable

Fabrication of Free-Standing ZnMn₂O₄ Mesoscale Tubular Arrays for Lithium-Ion Anodes with Highly Reversible Lithium Storage Properties

In this paper, ZnMn₂O₄ mesoscale tubular arrays on current collectors were successfully synthesized using a reactive template route combined with a postcalcination process through the shape-preserving conversion of ZnO nanorod arrays in aqueous solutions at room temperature. On the basis of the experimental analyses, including X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy, a plausible formation mechanism of ZnMn₂O₄ tubular arrays was proposed in which solid ZnO nanorods are gradually transformed to ZnMn₂O₄ tubules via a simple cation exchange process between Zn²⁺ and Mn²⁺, followed by a postannealing process. Moreover, the lithium storage properties of the as-prepared ZnMn₂O₄ tubular structures were investigated by applying the structures as an active electrode material without auxiliary additives. The ZnMn₂O₄ array electrodes showed an excellent discharge capacity of ca. 1198.3 mAh g^–1 on the first cycle and exhibited outstanding cycling durability, rate capability, and Coulombic efficiency. These results indicate that the free-standing tubular array architectures of ZnMn₂O₄ prepared directly on the current collector can be powerful candidates for a highly reversible lithium storage electrode platform

Highly Stretchable and Waterproof Electroluminescence Device Based on Superstable Stretchable Transparent Electrode

Realization of devices with enhanced stretchability and waterproof properties will significantly expand the reach of electronics. To this end, we herein fabricate an elastic transparent conductor that comprises silver nanowires (AgNWs) on a hydroxylated polydimethylsiloxane (PDMS) substrate covered by polyurethane urea (PUU), which is fully compatible with both materials. Carboxylic acid groups of PUU was designed to form hydrogen bonds with the carbonyl groups of poly­(vinylpyrrolidone) on the AgNW surface, resulting in an enhanced affinity of AgNWs for PUU. Exceptionally strong hydrogen bonds between PUU and the hydroxylated PDMS thus facilitate the achievement of water sealable, mechanically stable, and stretchable transparent electrodes. To fabricate stretchable electroluminescence (EL) devices, ZnS particles were mixed with PUU, and the mixture was coated onto the AgNWs/hydroxylated PDMS, followed by a face-to-face lamination with another identical electrode. The devices could be stretched up to 150% without a severe reduction in the emission intensity, and they survived 5000 cycles of 100% stretch–release testing. The high adhesion between PUU and PDMS even in water is responsible for the good waterproof characteristics of the EL devices. These results pave the way for realization of fully stretchable and waterproof electronic devices

Highly Stretchable and Mechanically Stable Transparent Electrode Based on Composite of Silver Nanowires and Polyurethane–Urea

Transparent electrodes based on conventional indium–tin oxide (ITO) can hardly meet the requirements of future generations of stretchable electronic devices, including artificial skins, stretchable displays, sensors, and actuators, because they cannot retain high conductivity under substantial stretching and bending deformation. Here we suggest a new approach for fabricating highly stretchable and transparent electrodes with good stability in environments where they would be stretched repeatedly. We designed polyurethane–urea (PUU), a urethane-based polymer, to enhance the adhesion between Ag nanowires (AgNWs) and poly­(dimethylsiloxane) (PDMS). The adhesion could be further improved when irradiated by intense pulsed light (IPL). After delicate optimization of the layered AgNW/PUU/PDMS structure, we fabricated a stretchable transparent electrode that could withstand 100 cycles of 50% stretching–releasing, with exceptionally high stability and reversibility. This newly developed electrode is therefore expected to be directly applicable to a wide range of high-performance, low-cost, stretchable electronic devices

Media 2: Integral imaging using a color filter pinhole array on a display panel

Originally published in Optics Express on 13 August 2012 (oe-20-17-18744

Media 1: Integral imaging using a color filter pinhole array on a display panel

Originally published in Optics Express on 13 August 2012 (oe-20-17-18744

Chromophore-Removal-Induced Conformational Change in Photoactive Yellow Protein Determined through Spectroscopic and X‑ray Solution Scattering Studies

Photoactive yellow protein (PYP) induces negative phototaxis in <i>Halorhodospira halophila</i> via photoactivation triggered by light-mediated chromophore isomerization. Chromophore isomerization proceeds via a volume-conserving isomerization mechanism due to the hydrogen-bond network and steric constraints inside the protein, and causes significant conformational changes accompanied by N-terminal protrusion. However, it is unclear how the structural change of the chromophore affects the remote N-terminal domain. To understand photocycle-related structural changes, we investigated the structural aspect of chromophore removal in PYP because it possesses a disrupted hydrogen-bond network similar to that in photocycle intermediates. A comparison of the structural aspects with those observed in the photocycle would give a clue related to the structural change mechanism in the photocycle_. Chromophore removal effects were assessed via UV–vis spectroscopy, circular dichroism, and X-ray solution scattering. Molecular shape reconstruction and an experiment-restrained rigid-body molecular dynamics simulation based on the scattering data were performed to determine protein shape, size, and conformational changes upon PYP bleaching. Data show that chromophore removal disrupted the holo-PYP structure, resulting in a small N-terminal protrusion, but the extent of conformational changes was markedly less than those in the photocycle. This indicates that disruption of the hydrogen-bond network alone in bleached PYP does not induce the large conformational change observed in the photocycle, which thus must result from the organized structural transition around the chromophore triggered by chromophore photoisomerization along with disruption of the hydrogen-bond network between the chromophore and the PYP core

Mechanically Robust and Healable Transparent Electrode Fabricated via Vapor-Assisted Solution Process

A mechanically robust, transparent, and healable electrode was successfully developed by embedding Ag nanowires (AgNWs) on the surface of polydimethylsiloxane-based polyurethane (PDMS-CPU) cross-linked by Diels–Alder (DA) adducts. The reversibility of the DA reaction enabled the heated dimethylformamide (DMF) vapor to induce de-cross-linking of the PDMS-CPU preformed as a substrate. A combination of the retro-DA reaction and the plasticizer effect softened the polymer surface, embedding the coated AgNWs on the surface of the polymer. With this simple postprocessing, the surface roughness and mechanical stability of the electrode were largely enhanced. Even with a 55 μm bending radius, which corresponds to a strain of 90%, the resistance of the electrode after 10 min of vapor treatment increased by 2.1% for inward bending and 5.3% for outward bending. This result shows a great potential of the proposed method, as it can also be used to fabricate various mechanically deformable transparent electrode. Furthermore, swelling of the PDMS-CPU film owing to the DMF vapor facilitated the healing properties of the scratched electrodes

Bifunctional Hybrid Catalysts with Perovskite LaCo_0.8Fe_0.2O₃ Nanowires and Reduced Graphene Oxide Sheets for an Efficient Li–O₂ Battery Cathode

In this paper, bifunctional catalysts consisting of perovskite LaCo_0.8Fe_0.2O₃ nanowires (LCFO NWs) with reduced graphene oxide (rGO) sheets were prepared for use in lithium–oxygen (Li–O₂) battery cathodes. The prepared LCFO@rGO composite was explored as a cathode catalyst for Li–O₂ batteries, resulting in an outstanding discharge capacity (ca. 7088.2 mAh g^–1) at the first cycle. Moreover, a high stability of the O₂-cathode with the LCFO@rGO catalyst was achieved over 56 cycles under the capacity limit of 500 mAh g^–1 with a rate of 200 mA g^–1, as compared to the Ketjenblack carbon and LCFO NWs. The enhanced electrochemical performance suggests that these hybrid composites of perovskite LCFO NWs with rGO nanosheets could be a perspective bifunctional catalyst for the cathode oxygen reduction and oxygen evolution reactions in the development of next-generation Li–O₂ battery cathodes

Length and Charge of the N‑terminus Regulate the Lifetime of the Signaling State of Photoactive Yellow Protein

Photoactive yellow protein (PYP) is one of the most extensively studied photoreceptors. Nevertheless, the role of the N-terminus in the photocycle and structural transitions is still elusive. Here, we attached additional amino acids to the N-terminus of PYP and investigated the effect of the length and charge of additional N-terminal residues using circular dichroism, two-dimensional nuclear magnetic resonance (2D-NMR), transient absorption (TA), and transient grating (TG) spectroscopic techniques. TA experiments showed that, except for negatively charged residues (5D-PYP), additional N-terminal residues of PYP generally enable faster dark recovery from the putative signaling state (pB2) to the ground state (pG). TG data showed that although the degree of structural changes can be controlled by adjusting specific amino acid residues in the extended N-terminus of N-terminal extended PYPs (NE-PYPs), the dark recovery times of wt-PYP and NE-PYPs, except for 5D-PYP, are independent of the structural differences between pG and pB2 states. These results demonstrate that the recovery time and the degree of structural change can be regulated by controlling the length and sequence of N-terminal residues of PYP. The findings in this study emphasize the need for careful attention to the remaining amino acid residues when designing recombinant proteins for genetic engineering purposes