The surface of water provides an excellent environment for gliding movement, in both nature and modern technology, from surface living animals such as the water strider, to LangmuirBlodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. In this method, namely, the pseudo free-standing tensile test, all specimen preparation and testing procedures are performed on the water surface, resulting in easy handling and almost frictionless sliding without specimen damage or substrate effects. We further utilize van der Waals adhesion for the damage-free gripping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging twodimensional materials.

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Carbon-nanotube (CNT)-based textile supercapacitors with MnO2 nanoparticles have excellent power and energy densities, but MnO2 nanoparticles can be delaminated during charge-discharge cycles, which results in significant degradation in capacitance. In this study, polypyrrole conductive polymer was coated on top of MnO2 nanoparticles that are deposited on CNT textile supercapacitor to prevent delamination of MnO2 nanoparticles. An increase of 38% in electrochemical energy capacity to 461 F/g was observed, while cyclic reliability also improved, as 93.8% of energy capacity was retained over 10 000 cycles. Energy density and power density were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in situ electrochemical-mechanical study revealed that polypyrrole-MnO2-coated CNT textile supercapacitor can retain 98.5% of its initial energy capacity upon application of 21% tensile strain and showed no observable energy storage capacity change upon application of 13% bending strain. After imposing cyclic bending of 750 000 cycles, the capacitance was retained to 96.3%. Therefore, the results from this study confirmed for the first time that the polypyrrole-MnO2-coated CNT textile can reliably operate with high energy and power densities with in situ application of both tensile and bending strains.

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO -composite electrode that is capable of undergoing "smart" reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm C and electrochemical performance with specific capacitance of 406.0 F g , energy/power densities of 40.6-47.8 Wh kg and 6.8-16.9 kW kg . The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge-discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.

more attention due to their low resistance and relatively high ductility. One of the main methods used previously to fabricate transparent and stretchable conductors with metal nanomaterials is to create buckling confi gurations of metal nanowires on stretchable polymers, which can be classifi ed as in-plane or out-of-plane buckling (wavy) confi gurations. [ 25,26 ] For example, Ho et al. reported the fabrication of transparent and stretchable conductors based on buckled Ag nanowire fi lms with in-plane or out-of-plane buckling confi gurations. [ 25 ] In a similar approach, it was also demonstrated that the prestrain mode (e.g., uniaxial or biaxial prestrain), extent of prestrain ( ε pre ), and adhesion between metal nanowires and a stretchable substrate are important factors that affect the stretchability of such conductors. [ 26 ] Another approach is to obtain fl exibility or stretchability by making nanowire-based networks or one-body mesh structures. [23][24][25][26][27][28][30][31][32][33][34][35] Most studies concerning one-body mesh structures have reported their applications for fl exible conductors, rather than stretchable ones, with only a few exceptions. [ 30,34 ] For example, Jang et al. reported stretchable conductors made from one-body Pt nanomesh. [ 30 ] Although their Pt nanomesh maintained its conductive properties at as much as 16% strain, its stretchability does not seem to be high enough for it to be used in true wearable electronic devices. This limited stretchability is probably due to the rigid nature of its tightly connected one-body confi guration. On the other hand, networks of metallic nanowires are rather promising for future use as transparent and stretchable electrodes. [25][26][27][28] In these cases, the sheet resistance of percolated networks of metallic nanowires is critically governed by the aspect ratio, areal density, and size dispersity of nanowires. [ 36 ] Recently, extremely long metal nanofi bers generated via electrospinning techniques have been in the limelight as an alternative to metal nanowires, due to their extremely high aspect ratios as well as the simple and cost-effective fabrication process used to produce them. [37][38][39] In particular, metal nanofi ber networks in the form of nanotroughs [ 37,38 ] and metal/polymer core-shell structures [ 39 ] generated using electrospinning techniques have low strain sensitivities under tensile strains up to 70% due to the high aspect ratio of the nanofi bers and the network structures into which they are arranged. However, combining the above-mentioned buckled and network confi gurations with metallized electrospun nanofi bers has not been investigated for the fabrication of transparent and stretchable conductors.Herein, a novel strategy for obtaining transparent and stretchable conductors is presented, one that employs these two main approaches simultaneously. To the best of our knowledge, this proposed confi guration of a buckled long nanofi ber In the past decade, the fi eld of stretchable electronics has gained importa...