Broadband Acoustoelectric Conversion Based on Oriented Polyacrylonitrile Nanofibers and Slit Electrodes for Generating Power from Airborne Noise.

Electrospun nanofiber acoustoelectric devices typically have a bandwidth in the range of 100-400 Hz, which limits their applications. This study demonstrates a novel device structure with tunable acoustoelectric bandwidth based on oriented electrospun polyacrylonitrile (PAN) nanofibers and slit electrodes. When the PAN nanofibers were arranged perpendicular to the slits, the devices had a much wider bandwidth than their parallel counterparts, while the latter had a bandwidth similar to that of randomly oriented nanofibers. In all devices, the electrical outputs follow a similar trend with the slit aspect ratio. However, the slit number only affected the electrical output without changing the bandwidth characteristic. We further showed that both the slit electrode and the oriented nanofiber membranes played a role in tuning the frequency response. Under sound, the vibration of the electrode caused the slit to be misaligned on both sides. The anisotropic tensile properties of the oriented nanofiber membranes allowed the fibers to stretch differently depending on their angle of alignment with the slits. Those perpendicular to the slits received more intense stretching, contributing to a wider bandwidth. The wider bandwidth increases the electrical output, especially when harvesting multifrequency sound. A 4 × 3 cm2 device made of five-slit electrodes (slit width × length, 2 mm × 30 mm) with PAN nanofibers perpendicular to the slits showed a bandwidth of 100-900 Hz and electrical outputs of 39.85 ± 1.34 V (current output 6.25 ± 0.18 µA) under 115 dB sound conditions, which is sufficient to power electromagnetic wireless transmitters. When one such slit device was used as a power supply and another as a sound sensor, they formed a completely self-powered wireless system that could detect sounds from various scenarios, such as high-speed trains, airports, highway traffic, and manufacturing industries. The energy can also be stored in lithium-ion batteries and capacitors. We hope that such novel devices will contribute to the development of highly efficient acoustoelectric technology for generating electrical energy from airborne noise.

Molecularly Resonant Metamaterials for Broad-Band Electromagnetic Stealth.

Electromagnetic (EM) metamaterial is a composite material with EM stealth properties, which is constructed by artificially reverse engineering metal split resonance rings (SRR). However, the greatest limitation of EM metamaterials is that they can only stealth at a fixed and lower frequency of EM waves, and modern processing techniques still cannot meet the accuracy requirements to fabric nano-size structural unit. Nano-sized and even ultra-small SRR at molecular level are promising arrays to realize the ability of EM stealth function at a higher frequency, although it has proven challenging to synthesize long, straight, connected molecular SRR, and also difficult to arrange those molecular SRR into a strict array. Here, the study overcomes this challenge and demonstrates that the fabric of polypyrrole molecular SRR achieves an ultra-small inner diameter of 2.49 Å and realizes the arrays arrangement at molecular level. Furthermore, the study exploits the EM stealth function and verifies that such arrays of molecular SRR with 2.49 Å have the ability to reach high-performance EM stealth in the range of 106 -1016 Hz. This design concept opens a pathway for developing new metamaterials with broadband EM wave stealth and also serves the wider range of new applications.

Structural Analysis of Oxidized Sucrose and Its Application as a Crease-Resistant Crosslinking Agent.

Oxidized sucrose is a non-formaldehyde crosslinking agent with many applications in polymer crosslinking and modification, such as in the preparation of starch films and protein films. However, research on the structure of oxidized sucrose is lacking. In this paper, oxidized sucrose was synthesized through selective oxidation of sodium periodate. By LC-MS, FTIR, TGA, NMR, and HRMS analyses, it was shown that oxidized sucrose existed in the form of a hydrate, and the tetraaldehyde oxidized sucrose could isomerize into the form of two six-membered hemiacetal rings. The structure of oxidized sucrose was also verified by theoretical calculations. Furthermore, the diffusional properties of oxidized sucrose were investigated by the rolling-film method. Finally, it was found that oxidized sucrose used as a crosslinking agent could effectively improve the wrinkle recovery performance of cotton fabrics.

Research of a Novel Ag Temperature Sensor Based on Fabric Substrate Fabricated by Magnetron Sputtering.

TPU-coated polyester fabric was used as the substrate of a flexible temperature sensor and Ag nanoparticles were deposited on its surface as the temperature sensing layer by the magnetron sputtering method. The effects of sputtering powers and heat treatment on properties of the sensing layers, such as the temperature coefficient of resistance (TCR), linearity, hysteresis, drift, reliability, and bending resistance, were mainly studied. The results showed that the TCR (0.00234 °C-1) was the highest when sputtering power was 90 W and sputtering pressure was 0.8 Pa. The crystallinity of Ag particles would improve, as the TCR was improved to 0.00262 °C-1 under heat treatment condition at 160°. The Ag layer obtained excellent linearity, lower hysteresis and drift value, as well as good reliability and bending resistance when the sputtering power was 90 W. The flexible temperature sensor based on the coated polyester fabric improved the softness and comfortableness of sensor, which can be further applied in intelligent wearable products.

Recent Progress in Magnetron Sputtering Technology Used on Fabrics.

The applications of magnetron sputtering technology on the surface coating of fabrics have attracted more and more attention from researchers. Over the past 15 years, researches on magnetron sputtering coated fabrics have been mainly focused on electromagnetic shielding, bacterial resistance, hydrophilic and hydrophobic properties and structural color etc. In this review, recent progress of the technology is discussed in detail, and the common target materials, technologies and functions and characterization of coated fabrics are summarized and analyzed. Finally, the existing problems and future prospects of this developing field are briefly proposed and discussed.

TiO2 seeded on nitrogen-doped porous carbon nanofibers for superior electrochemical performance as freestanding anodes of lithium-ion batteries.

Fibrous mats piled by nitrogen-doped porous carbon nanofibers with seeded TiO2 are fabricated and punched directly into circles as lithium-ion battery anodes. The seeding structure is composed of semi-wrapped TiO2 nanoparticles on carbon nanofibers (CNFs) coated with a thin layer of carbon. Synchronously, pores with various widths are formed on CNFs. As a freestanding anode, an initial discharge capacity of 615 mAh g-1 with a coulombic efficiency of 56% is reached, and 322 mAh g-1 is obtained after 100 cycles at a current density of 100 mA g-1. This is assigned to the increasing number of active sites for the lithium ion from pores with various widths and improved conductivity originating from nitrogen doping. Superior rate performance (179 mAh g-1 at the current density of 2000 mA g-1) under various current densities compared with that of other counterparts is attributed to the structural stability originating from the seeding structure with the help of the C-O-Ti bond. An additional 800 cycles are displayed at the current density of 2000 mA g-1, and superior stability is also exhibited.

Eco-Friendly and Highly Efficient Enzyme-Based Wool Shrinkproofing Finishing by Multiple Padding Techniques.

Wool fibers usually need shrinkproofing finishing. The enzyme process is an eco-friendly technology but the traditional exhaustion treatment usually takes excessive time. This study developed a novel multiple padding shrinkproofing process of wool with Savinase 16L and an organic phosphine compound {[HO(CH2)n]3P, n ∈ (1, 10)}. SEM and XPS analyses were employed to compare the wool treated respectively by exhaustion and by padding to reveal the effect of multiple padding. The results showed that treated wool fiber achieved the requirement of machine-washable (area shrinkage less than 8% according to standard TM 31 5 × 5A) in 2.5 min by the padding process. The padding process can control the adsorbance of enzyme on wool, which makes treatment more uniform and avoids strong damage of the wool. Also, the removal efficiency of the disulfide bond was about 15 times as much as in the exhaustion treatment in 2.5 min. The average catalytic rate of the padding process was 14 times faster than the exhaustion process, and the process time (2.5 min) decreased by 32.5 min compared with the exhaustion process (35 min). Multiple padding techniques can achieve continuous production and replace the environmentally harmful chlorination process. Our results provide the underlying insights needed to guide the research of the enzyme process application.

Effects of Graphene Oxide on the Structure and Properties of Regenerated Wool Keratin Films.

Much research has focused on improvement of the structural and mechanical properties of regenerated keratin materials by physical or chemical methods in recent years. In this research, regenerated keratin materials were modified with graphene oxide (GO). The properties of modified keratin films and the mechanism of interaction between GO and keratin macromolecules were studied. The SEM and XRD test results showed that the orientation of keratin macromolecules could be effectively improved by GO, which favored improvement of the keratin material's crystallinity and made the films more uniform and compact. The thermal stability and mechanical properties of GO-modified keratin films were also improved significantly. At the same time, the reaction mechanism between keratin and GO materials was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), FT-IR, and Raman spectroscopy. It was shown that there was no chemical reaction between GO and keratin molecules, and the interaction between them was mainly via hydrogen bonding and van der Waals forces.