Gui-Wen Huang

Enhanced Microwave Absorption Performance of Coated Carbon Nanotubes by Optimizing the Fe3O4 Nanocoating Structure

It is well accepted that the microwave absorption performance (MAP) of carbon nanotubes (CNTs) can be enhanced via coating magnetic nanoparticles on their surfaces. However, it is still unclear if the magnetic coating structure has a significant influence on the microwave absorption behavior. In this work, nano-Fe3O4 compact-coated CNTs (FCCs) and Fe3O4 loose-coated CNTs (FLCs) are prepared using a simple solvothermal method. The MAP of the Fe3O4-coated CNTs is shown to be adjustable via controlling the Fe3O4 nanocoating structure. The results reveal that the overall MAP of coated CNTs strongly depends on the magnetic coating structure. In addition, the FCCs show a much better MAP than the FLCs. It is shown that the microwave absorption difference between the FLCs and FCCs is due to the disparate complementarities between the dielectric loss and the magnetic loss, which are related to the coverage density of Fe3O4 nanoparticles on the surfaces of CNTs. For FCCs, the mass ratio of CNTs to Fe3+ is then optimized to maximize the effective complementarities between the dielectric loss and the magnetic loss. Finally, a comparison is made with the literature on Fe3O4-carbon-based composites. The FCCs at the optimized CNT to Fe3+ ratio in the present work show the most effective specific RLmin (28.7 dB·mm-1) and the widest effective bandwidth (RL < -10 dB) (8.3 GHz). The excellent MAP of the as-prepared FCC sample is demonstrated to result from the consequent dielectric relaxation process and the improved magnetic loss. Consequently, the structure-property relationship revealed is significant for the design and preparation of CNT-based materials with effective microwave absorption.

Wearable Electronics of Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing.

Wearable electronics used in smart clothing for healthcare monitoring or personalized identification is a new and fast-growing research topic. The challenge is that the electronics has to be simultaneously highly stretchable, mechanically robust and water-washable, which is unreachable for traditional electronics or previously reported stretchable electronics. Herein we report the wearable electronics of sliver nanowire (Ag-NW)/poly(dimethylsiloxane) (PDMS) nanocomposite which can meet the above multiple requirements. The electronics of Ag-NW/PDMS nanocomposite films is successfully fabricated by an original pre-straining and post-embedding (PSPE) process. The composite film shows a very high conductivity of 1.52 × 104 S cm−1 and an excellent electrical stability with a small resistance fluctuation under a large stretching strain. Meanwhile, it shows a robust adhesion between the Ag-NWs and the PDMS substrate and can be directly machine-washed. These advantages make it a competitive candidate as wearable electronics for smart clothing applications.

Ternary Ag/epoxy adhesive with excellent overall performance.

Excellent electrical conductivity (EC) generally conflicts with high lap shear strength (LSS) for electrically conductive adhesives (ECAs) since EC increases while LSS decreases with increasing conductive filler content. In this work, the ECAs with the excellent overall performance are developed based on the ternary hybrid of Ag microflakes (Ag-MFs), Ag nanospheres (Ag-NSs), and Ag nanowires (Ag-NWs). First, a low silver content adhesive system is determined. Then, the effects of the relative contents of Ag fillers on the EC and the LSS are studied. It is shown that a small amount of Ag-NSs or Ag-NWs can dramatically improve the EC for the Ag-MF/epoxy adhesives. The Ag-NSs and Ag-NWs with appropriate contents have a synergistic effect in improving the EC. Meanwhile, the LSS of the as-prepared adhesive with the appropriate Ag contents reaches an optimal value. Both the EC and the LSS of the as-prepared ternary hybrid ECA with a low content of 40 wt % Ag are higher than those of the commercial ECAs filled with the Ag-MF content over 60 wt %. Finally, the ternary hybrid ECA with the optimal formulation is shown to be promising for printing the radio frequency identification tag antennas as an immediate application example.

Electrical Switch for Smart pH Self-Adjusting System Based on Silver Nanowire/Polyaniline Nanocomposite Film

A sensitive pH-triggered electrical switch is demonstrated by using a layer-structured silver nanowire/polyaniline nanocomposite film fabricated via an easy vertical spinning method. The as-prepared nanocomposite film shows the high electrical conductivity of 1.03 × 10(4) S cm(-1) at the Ag-NW areal density of 0.84 mg cm(-2) and a good cycling stability. Particularly, because of the layered structure, the switch achieves a very high contrast ratio of ca. 9 × 10(8), which is 2-6 orders higher than that reported previously. The high electrical conductivity and the high switching ratio make the layer-structured nanocomposite film a sensitive switch candidate for pH-responsive systems. Finally, a smart pH self-adjusting switching system is successfully designed using the as-prepared layer-structured nanocomposite film.

Controllable fabrication and magnetic-field assisted alignment of Fe3O4-coated Ag nanowires via a facile co-precipitation method

In order to further improve their properties and functions and extend their applications in various technology fields, it is desired to decorate Ag NWs with foreign magnetic materials. In this work, silver nanowires (Ag NWs) decorated with magnetite nanoparticles have been fabricated by a facile co-precipitation method, which was conducted in de-ionized water with iron ions and Ag NWs as starting materials. The as-prepared Fe3O4-coated Ag NWs are well characterized by XRD, XPS, FT-IR, SEM and TEM techniques. The amount of magnetite nanoparticles decorated on the Ag NWs can be controlled by adjusting the initial mass ratio of iron ions to Ag NWs. The Fe3O4-coated Ag NWs show good electrical and ferromagnetic properties at room temperature and their electrical and magnetic properties depend on the amount of magnetite nanoparticles decorated on the Ag NWs. The Fe3O4-coated Ag NWs can be highly aligned by an external magnetic field. The results suggest that the alignment of the decorated Ag NWs displays significant dependences on the amount of magnetite nanoparticles.

Rapid Laser Printing of Paper-Based Multilayer Circuits

Laser printing has been widely used in daily life, and the fabricating process is highly efficient and mask-free. Here we propose a laser printing process for the rapid fabrication of paper-based multilayer circuits. It does not require wetting of the paper, which is more competitive in manufacturing paper-based circuits compared to conventional liquid printing process. In the laser printed circuits, silver nanowires (Ag-NWs) are used as conducting material for their excellent electrical and mechanical properties. By repeating the printing process, multilayer three-dimensional (3D) structured circuits can be obtained, which is quite significant for complex circuit applications. In particular, the performance of the printed circuits can be exactly controlled by varying the process parameters including Ag-NW content and laminating temperature, which offers a great opportunity for rapid prototyping of customized products with designed properties. A paper-based high-frequency radio frequency identification (RFID) label with optimized performance is successfully demonstrated. By adjusting the laminating temperature to 180 °C and the top-layer Ag-NW areal density to 0.3 mg cm(-2), the printed RFID antenna can be conjugately matched with the chip, and a big reading range of ∼12.3 cm with about 2.0 cm over that of the commercial etched Al antenna is achieved. This work provides a promising approach for fast and quality-controlled fabrication of multilayer circuits on common paper and may be enlightening for development of paper-based devices.

Novel vertical spinning preparation of free-standing carbon nanotube–polyaniline composite films with high electrical conductivity

A novel vertical spinning (VS) process is reported for fabricating free-standing carbon nanotube (CNT)–polyaniline (PANI) composite films with high electrical conductivity (EC). In the VS process, a high centrifugal force is exerted on the PANI solution containing CNTs to achieve a uniform dispersion of CNTs in the composites; meanwhile, the high aspect ratio of CNTs is greatly maintained to a high degree (75%). These contribute to the high EC of the CNT–PANI films since the EC benefits from both the good dispersion and the high aspect ratio of CNTs. The EC of the as-prepared composite film with the 10 wt% CNTs has a value above 150 S cm−1, which is much higher than that at the same CNT content reported previously in the literature. For the purpose of comparison, the CNT–PANI composite films were prepared via the commonly used plane casting process. Moreover, the sandwich-structured PANI–CNT–PANI composite films were synthesized via the VS process to illustrate another advantage of this process in manipulating the distribution of fillers in the composites. The CNT–PANI composite films prepared by the VS process show the highest EC. The sandwiched structure shows a reasonably high conductivity and a relatively low percolation threshold among the three composite films.

Electrical anisotropy and multidimensional pressure sensor of aligned Fe3O4@silver nanowire/polyaniline composite films under an extremely low magnetic field

A low magnetic field is preferred in preparing aligned composites since a high magnetic field may be harmful to human health. In this study, fine-sized Fe3O4 nanoparticles with diameters of several nanometers are decorated on the surface of Ag-NWs (Fe3O4@Ag-NWs). Controllably aligned Fe3O4@Ag nanowire (Ag-NW)/polyaniline (PANI) composite films are then prepared under an extremely low magnetic field of 26–42 mT, which is much lower than those reported previously (0.1–10 T). As a result, the as-prepared Fe3O4@Ag-NW/PANI composite films show an excellent electrical conductivity from 5.5 × 102 to 4.1 × 103 S cm−1 and a controllable electrical conductivity anisotropy from 1.1 to 6.7. Furthermore, the anisotropic responsive behavior of the Fe3O4@Ag-NW/PANI composite film makes it an ideal candidate for the fabrication of multidimensional pressure sensors. In most studies, conventional strain sensors are fabricated because they are only capable of detecting strains in one single direction due to a strongly coupled electrical conductance change. Finally, the fabrication of a multidimensional pressure sensor based on the as-prepared Fe3O4@Ag-NW/PANI composite film is demonstrated for the first time and a unique anisotropic pressure sensitivity is reported.

Reduced Graphene Oxide Coating with Anti-corrosion and Electrochemical Property Enhancing Effects Applied in Hydrogen Storage System.

Low-capacity retention is the most prominent problem of the magnesium nickel alloy (Mg2Ni), which prevents it from being commercially applied. Here, we propose a practical method for enhancing the cycle stability of the Mg2Ni alloy. Reduced graphene oxide (rGO) possesses a graphene-based structure, which could provide high-quality barriers that block the hydroxyl in the aqueous electrolyte; it also possesses good hydrophilicity. rGO has been successfully coated on the amorphous-structured Mg2Ni alloy via electrostatic assembly to form the rGO-encapsulated Mg2Ni alloy composite (rGO/Mg2Ni). The experimental results show that ζ potentials of rGO and the modified Mg2Ni alloy are totally opposite in water, with values of -11.0 and +22.4 mV, respectively. The crumpled structure of rGO sheets and the contents of the carbon element on the surface of the alloy are measured using scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometry. The Tafel polarization test indicates that the rGO/Mg2Ni system exhibits a much higher anticorrosion ability against the alkaline solution during charging/discharging. As a result, high-capacity retentions of 94% (557 mAh g-1) at the 10th cycle and 60% (358 mAh g-1) at the 50th cycle have been achieved, which are much higher than the results on Mg2Ni capacity retention combined with the absolute value reported so far to our knowledge. In addition, both the charge-transfer reaction rate and the hydrogen diffusion rate are proven to be boosted with the rGO encapsulation. Overall, this work demonstrates the effective anticorrosion and electrochemical property-enhancing effects of rGO coating and shows its applicability in the Mg-based hydrogen storage system.

A Novel Type of Battery–Supercapacitor Hybrid Device with Highly Switchable Dual Performances Based on a Carbon Skeleton/Mg2Ni Free-Standing Hydrogen Storage Electrode

The sharp proliferation of high power electronics and electrical vehicles has promoted growing demands for power sources with both high energy and power densities. Under these circumstances, battery-supercapacitor hybrid devices are attracting considerable attention as they combine the advantages of both batteries and supercapacitors. Here, a novel type of hybrid device based on a carbon skeleton/Mg2Ni free-standing electrode without the traditional nickel foam current collector is reported, which has been designed and fabricated through a dispersing-freeze-drying method by employing reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) as a hybrid skeleton. As a result, the Mg2Ni alloy is able to deliver a high discharge capacity of 644 mAh g-1 and, more importantly, a high cycling stability with a retention of over 78% after 50 charge/discharge cycles have been achieved, which exceeds almost all the results ever reported on the Mg2Ni alloy. Simultaneously, the electrode could also exhibit excellent supercapacitor performances including high specific capacities (296 F g-1) and outstanding cycling stability (100% retention after 100 cycles). Moreover, the hybrid device can switch between battery and supercapacitor modes immediately as needed during application. These features make the C skeleton/alloy electrode a highly promising candidate for battery-supercapacitor hybrid devices with high power/energy density and favorable cycling stability.