Fabrication of junction-free Cu nanowire networks via Ru-catalyzed electroless deposition and their application to transparent conducting electrodes.

Over the past few years, metal nanowire networks have attracted attention as an alternative to transparent conducting oxide materials such as indium tin oxide for transparent conducting electrode applications. Recently, electrodeposition of metal on nanoscale template is widely used for formation of metal network. In the present work, junctionless Cu nanowire networks were simply fabricated on a substrate by forming a nanostructured Ru with 80 nm width as a seed layer, followed by direct electroless deposition of Cu. By controlling the density of Ru nanowires or the electroless deposition time, we readily achieve desired transmittance and sheet resistance values ranging from ∼1 kΩ sq-1at 99% to 9 Ω sq-1at 89%. After being transferred to flexible substrates, the nanowire networks exhibited no obvious increase in resistance during 8000 cycles of a bending test to a radius of 2.5 mm. The durability was verified by evaluation of its heating performance. The maximum temperature was greater than 180 °C at 3 V and remained constant after three repeated cycles and for 10 min. Transmission electron microscopy and x-ray diffraction studies revealed that the adhesion between the electrolessly deposited Cu and the seed Ru nanowires strongly influenced the durability of the core-shell structured nanowire-based heaters.

All-Organic, Solution-Processed, Extremely Conformal, Mechanically Biocompatible, and Breathable Epidermal Electrodes.

Conformal integration of an epidermal device with the skin, as well as sweat and air permeability, are crucial to reduce stress on biological tissues. Nanofiber-based porous mesh structures (breathable devices) are commonly utilized to prevent skin problems. Noble metals are normally deposited on nanomesh substrates to form breathable electrodes. However, these are expensive and require high-vacuum processes involving time-consuming multistep procedures. Organic materials are suitable alternatives that can be simply processed in solution. We report a simple, cost-effective, mechanically biocompatible, and breathable organic epidermal electrode for biometric devices. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is sprayed on a nanofiber-mesh structure, treated using only heat and water to enhance its biocompatibility and conductivity, and used as the electrode. The treatment is accomplished using an autoclave, simultaneously reducing the electrical resistance and sterilizing the electrode for practical use. This research can lead to affordable and biocompatible epidermal electrodes with improved suitability for various biomedical applications.

Recent Advances on Nanofiber Fabrications: Unconventional State-of-the-Art Spinning Techniques.

In this review, we describe recent relevant advances in the fabrication of polymeric nanofibers to address challenges in conventional approaches such as electrospinning, namely low throughput and productivity with low size uniformity, assembly with a regulated structure and even architecture, and location with desired alignments and orientations. The efforts discussed have mainly been devoted to realize novel apparatus designed to resolve individual issues that have arisen, i.e., eliminating ejection tips of spinnerets in a simple electrospinning system by effective control of an applied electric field and by using mechanical force, introducing a uniquely designed spinning apparatus including a solution ejection system and a collection system, and employing particular processes using a ferroelectric material and reactive precursors for atomic layer deposition. The impact of these advances to ultimately attain a fabrication technique to solve all the issues simultaneously is highlighted with regard to manufacturing high-quality nanofibers with high- throughput and eventually, practically implementing the nanofibers in cutting-edge applications on an industrial scale.

A Highly Porous Nonwoven Thermoplastic Polyurethane/Polypropylene-Based Triboelectric Nanogenerator for Energy Harvesting by Human Walking.

: A highly porous nonwoven thermoplastic polyurethane (TPU)/Polypropylene (PP) triboelectric nanogenerator (N-TENG) was developed. To fabricate the triboelectric layers, the TPU nanofiber was directly electrospun onto the nonwoven PP at different basis weights (15, 30, and 50 g/m2). The surface morphologies and porosities of the nonwoven PP and TPU nanofiber mats were characterized by field-emission scanning electron microscopy and porosimetry. The triboelectric performance of the nonwoven TPU/PP based TENG was found to improve with an increase in the basis weight of nonwoven PP. The maximum output voltage and current of the TPU/PP N-TENG with 50% PP basis weight reached 110.18 ± 6.06 V and 7.28 ± 0.67 µA, respectively, due to high air volume of nonwoven without spacers. In order to demonstrate its practical application as a generator, a TPU/PP N-TENG-attached insole for footwear was fabricated. The N-TENG was used as a power source to turn on 57 light-emitting diodes through human-walking, without any charging system. Thus, owing to its excellent energy-conversion performance, simple fabrication process, and low cost, the breathable and wearable nonwoven fiber-based TENG is suitable for large-scale production, to be used in wearable devices.

Nano- And Microfiber-Based Fully Fabric Triboelectric Nanogenerator For Wearable Devices.

The combination of the triboelectric effect and static electricity as a triboelectric nanogenerator (TENG) has been extensively studied. TENGs using nanofibers have advantages such as high surface roughness, porous structure, and ease of production by electrospinning; however, their shortcomings include high-cost, limited yield, and poor mechanical properties. Microfibers are produced on mass scale at low cost; they are solvent-free, their thickness can be easily controlled, and they have relatively better mechanical properties than nanofiber webs. Herein, a nano- and micro-fiber-based TENG (NMF-TENG) was fabricated using a nylon 6 nanofiber mat and melt blown nonwoven polypropylene (PP) as triboelectric layers. Hence, the advantages of nanofibers and microfibers are maintained and mutually complemented. The NMF-TENG was manufactured by electrospinning nylon 6 on the nonwoven PP, and then attaching Ni coated fabric electrodes on the top and bottom of the triboelectric layers. The morphology, porosity, pore size distribution, and fiber diameters of the triboelectric layers were investigated. The triboelectric output performances were confirmed by controlling the pressure area and basis weight of the nonwoven PP. This study proposes a low-cost fabrication process of NMF-TENGs with high air-permeability, durability, and productivity, which makes them applicable to a variety of wearable electronics.

Breathable Nanomesh Humidity Sensor for Real-Time Skin Humidity Monitoring.

The importance of monitoring the condition of skin is increasing as its relevance to health is becoming more well understood. Inappropriate humidity levels can cause atopic dermatitis or hair loss. However, conventional film substrates used in electronic skin monitoring devices cause accumulation of sweat or gas between the device and biological tissue, leading to negative effects in long-term humidity measurements. Thus, real-time measurements of skin humidity over long periods are difficult using conventional film devices. Here, a breathable nanomesh humidity sensor that can monitor skin humidity for a long time is developed by using biocompatible materials such as gold, poly(vinyl alcohol), and Parylene C. The sensor presents excellent gas and sweat permeability and precisely detects the humidity level of an object for a long time. This study demonstrates the successful real-time detection of the humidity level from human skin and also detects the relative humidity of a plant surface over a prolonged period. This sensor is expected to have wide applicability for cultivating delicate plants as well as to reveal correlations between skin humidity and disease for biomedical applications.

Effect of Carbonation on Abrasion Resistance of Alkali-Activated Slag with Various Activators.

The effect of carbonation on the abrasion resistance of alkali-activated slag (AAS) was investigated. Various activator sets were selected for synthesizing AAS specimens, and the compressive strength was measured before and after carbonation. The abrasion resistance of the specimens was measured in accordance with the ASTM C944 test method. The relationship between the mass loss caused by abrasion and compressive strength was analyzed to understand the effect of matrix strength on abrasion resistance. Test results showed that the decrease in compressive strength of AAS specimens by carbonation reduced their abrasion resistance. In addition, the abrasion resistance of AAS before and after carbonation was sensitively influenced by activator type. It can be concluded that additional caution is required when using AAS where abrasion may have occurred.

Sound Absorption and Insulation Properties of a Polyurethane Foam Mixed with Electrospun Nylon-6 and Polyurethane Nanofibre Mats.

In recent years, noise has become a serious hazard and can have permanent biological and psychological effects on humans and other organisms in nature. Textile materials are commonly used as absorbent acoustic materials for noise reduction. This work examines the use of electrospun nylon-6 and polyurethane nanofibres (PU NFs) to improve the sound absorption and sound insulation properties of polyurethane foam. In this work, nylon-6 and polyurethane nanofibres were prepared by an electrospinning technique and were glued to a polyurethane foam. The sound absorption coefficient of the materials was measured by the impedance tube method. An impedance tube was used to measure the sound absorption and airborne sound insulation. The results showed decreased sound absorption properties, whereas the sound insulation was highly enhanced when polyurethane/nanofibre hybrids were used, as compared to the pristine polyurethane foam. Furthermore, the sound insulation properties of polyurethane foam were highly enhanced when the foam was combined with nylon-6 NFs, compared with the polyurethane foam with PU NFs. Therefore, by investigating the acoustic characteristics of electrospun nylon-6 and PU nanofibres, we believe that this study can broaden the application of electrospun nanofibres for sound pollution control.

Functional neuroanatomy associated with natural and urban scenic views in the human brain: 3.0T functional MR imaging.

OBJECTIVE: By using a functional magnetic resonance imaging (fMRI) technique we assessed brain activation patterns while subjects were viewing the living environments representing natural and urban scenery. MATERIALS AND METHODS: A total of 28 healthy right-handed subjects underwent an fMRI on a 3.0 Tesla MRI scanner. The stimulation paradigm consisted of three times the rest condition and two times the activation condition, each of which lasted for 30 and 120 seconds, respectively. During the activation period, each subject viewed natural and urban scenery, respectively. RESULTS: The predominant brain activation areas observed following exposure to natural scenic views in contrast with urban views included the superior and middle frontal gyri, superior parietal gyrus, precuneus, basal ganglia, superior occipital gyrus, anterior cingulate gyrus, superior temporal gyrus, and insula. On the other hand, the predominant brain activation areas following exposure to urban scenic views in contrast with natural scenes included the middle and inferior occipital gyri, parahippocampal gyrus, hippocampus, amygdala, anterior temporal pole, and inferior frontal gyrus. CONCLUSION: Our findings support the idea that the differential functional neuroanatomies for each scenic view are presumably related with subjects' emotional responses to the natural and urban environment, and thus the differential functional neuroanatomy can be utilized as a neural index for the evaluation of friendliness in ecological housing.

Human brain activation in response to visual stimulation with rural and urban scenery pictures: a functional magnetic resonance imaging study.

Human brain activation was assessed in terms of eco-friendliness while viewing still photographs depicting rural and urban surrounding environments with the use of a functional magnetic resonance imaging technique. A total of 30 subjects who had both rural and urban life experiences participated in this study. In order to explore the common and differential activation maps yielded by viewing two extreme types of scenery, random effect group analysis was performed with the use of one-sample and two-sample t-tests. Activation of the anterior cingulate gyrus, globus pallidus, putamen and head of the caudate nucleus was dominant during rural scenery viewing, whereas activation of the hippocampus, parahippocamus and amygdala was dominant during urban scenery viewing (p<0.01). These findings allow better characterization of neural activation, suggesting an inherent preference towards nature-friendly living. Such a theoretical acquisition may have an important practical impact in view of potential applications for bio-housing and the development of environmental psychology-related areas.