Sodium alginate reinforced polyacrylamide/xanthan gum double network ionic hydrogels for stress sensing and self-powered wearable device applications.

Strong and ductile sodium alginate (SA) reinforced polyacrylamide (PAM)/xanthan gum (XG) double network ionic hydrogels were constructed for stress sensing and self-powered wearable device applications. In the designed network of PXS-Mn+/LiCl (short for PAM/XG/SA-Mn+/LiCl, where Mn+ stands for Fe3+, Cu2+ or Zn2+), PAM acts as a flexible hydrophilic skeleton, and XG functions as a ductile second network. The macromolecule SA interacts with metal ion Mn+ to form a unique complex structure, significantly improving the mechanical strength of the hydrogel. The addition of inorganic salt LiCl endows the hydrogel with high electrical conductivity, and meanwhile reduces the freezing point and prevents water loss of the hydrogel. PXS-Mn+/LiCl exhibits excellent mechanical properties and ultra-high ductility (a fracture tensile strength up to 0.65 MPa and a fracture strain up to 1800%), and high stress-sensing performance (a high GF up to 4.56 and pressure sensitivity of 0.122). Moreover, a self-powered device with a dual-power-supply mode, i.e., PXS-Mn+/LiCl-based primary battery and TENG, and a capacitor as the energy storage component was constructed, which shows promising prospects for self-powered wearable electronics.

Solution-Processable Conductive Composite Hydrogels with Multiple Synergetic Networks toward Wearable Pressure/Strain Sensors.

A biocompatible, flexible, yet robust conductive composite hydrogel (CCH) for wearable pressure/strain sensors has been achieved by an all-solution-based approach. The CCH is rationally constructed by in situ polymerization of aniline (An) monomers in the polyvinyl alcohol (PVA) matrix, followed by the cross-linking of PVA with glutaraldehyde (GA) as the cross-linker. The unique multiple synergetic networks in the CCH including strong chemical covalent bonds and abundance of weak physical cross-links, i.e., hydrogen bondings and electrostatic interactions, impart excellent mechanical strength (a fracture tensile strength of 1200 kPa), superior compressibility (ε = 80%@400 kPa), outstanding stretchability (a fracture strain of 670%), high sensitivity (0.62 kPa-1 at a pressure range of 0-1.0 kPa for pressure sensing and a gauge factor of 3.4 at a strain range of 0-300% for strain sensing, respectively), and prominent fatigue resistance (1500 cycling). As the flexible wearable sensor, the CCH is able to monitor different types of human motion and diagnostically distinguish speaking. As a proof of concept, a sensing device has been designed for the real-time detection of 2D distribution of weight or pressure, suggesting its promising potentials for electronic skin, human-machine interaction, and soft robot applications.

Controllable organic magnetoresistance in polyaniline coated poly(p-phenylene-2,6-benzobisoxazole) short fibers.

Herein, we first report a tunable organic magnetoresistance (OMAR) effect in polyaniline (PANI) coated acid treated poly(p-phenylene-2,6-benzobisoxazole) (t-PBO) short fibers. This unique OMAR is interpreted using the paramagnetic nature of PBO molecules combined with the localization length a0 calculated from the wave-function shrinkage model and forward interference model.

Strengthened Magnetoresistive Epoxy Nanocomposite Papers Derived from Synergistic Nanomagnetite-Carbon Nanofiber Nanohybrids.

Novel papers based on epoxy nanocomposites with magnetite and carbon nanofiber (CNF) nanohybrids, without any surface modification to the nanofillers, show combined conductive, magnetic, and magnetoresistive properties. Negative magnetoresistance (MR) is observed in synthesized epoxy nanohybrid papers for the first time. These papers have potential applications for flexible electronics, magnetoresistive sensors, and the printing industry.

Electrically conductive polypropylene nanocomposites with negative permittivity at low carbon nanotube loading levels.

Polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites were prepared by coating CNTs on the surface of gelated/swollen soft PP pellets. The electrical conductivity (σ) studies revealed a percolation threshold of only 0.3 wt %, and the electrical conductivity mechanism followed a 3-d variable range hopping (VRH) behavior. At lower processing temperature, the CNTs formed the network structure more easily, resulting in a higher σ. The fraction of γ-phase PP increased with increasing the pressing temperature. The CNTs at lower loading (0.1 wt %) served as nucleating sites and promoted the crystallization of PP. The CNTs favored the disentanglement of polymer chains and thus caused an even lower melt viscosity of nanocomposites than that of pure PP. The calculated optical band gap of CNTs was observed to increase with increasing the processing temperature, i.e., 1.55 eV for nanocomposites prepared at 120 °C and 1.70 eV prepared at 160 and 180 °C. Both the Drude model and interband transition phenomenon have been used for theoretical analysis of the real permittivity of the nanocomposites.

Optimal Electrocatalytic Pd/MWNTs Nanocatalysts toward Formic Acid Oxidation.

The operating conditions such as composition of electrolyte and temperature can greatly influence the formic acid (HCOOH) oxidation reaction (FAOR). Palladium decorated multi-walled carbon nanotubes (Pd/MWNTs) were successfully synthesized and employed as nanocatalysts to explore the effects of formic acid, sulfuric acid (H2SO4) concentration and temperature on FAOR. Both the hydrogen adsorption in low potential range and the oxidation of poisoning species during the high potential range in cyclic voltammetry were demonstrated to contribute to the enhanced electroactivity of Pd/MWNTs. The as-synthesized Pd/MWNTs gave the best performance under a condition with balanced adsorptions of HCOOH and H2SO4 molecules. The dominant dehydrogenation pathway on Pd/MWNTs can be largely depressed by the increased dehydration pathway, leading to an increased charge transfer resistance (Rct ). Increasing HCOOH concentration could directly increase the dehydration process proportion and cause the production of COads species. H2SO4 as donor of H+ greatly facilitated the onset oxidation of HCOOH in the beginning process but it largely depressed the HCOOH oxidation with excess amount of H+. Enhanced ion mobility with increasing the temperature was mainly responsible for the increased current densities, improved tolerance stabilities and reduced Rct values, while dehydration process was also increased simultaneously.

Multifunctional Carbon Nanostructures for Advanced Energy Storage Applications.

Carbon nanostructures-including graphene, fullerenes, etc.-have found applications in a number of areas synergistically with a number of other materials. These multifunctional carbon nanostructures have recently attracted tremendous interest for energy storage applications due to their large aspect ratios, specific surface areas, and electrical conductivity. This succinct review aims to report on the recent advances in energy storage applications involving these multifunctional carbon nanostructures. The advanced design and testing of multifunctional carbon nanostructures for energy storage applications-specifically, electrochemical capacitors, lithium ion batteries, and fuel cells-are emphasized with comprehensive examples.

Electrochemical energy storage by polyaniline nanofibers: high gravity assisted oxidative polymerization vs. rapid mixing chemical oxidative polymerization.

Polyaniline (PANI) nanofibers prepared by high gravity chemical oxidative polymerization in a rotating packed bed (RPB) have demonstrated a much higher specific capacitance of 667.6 F g(-1) than 375.9 F g(-1) of the nanofibers produced by a stirred tank reactor (STR) at a gravimetric current of 10 A g(-1). Meanwhile, the cycling stability of the electrode is 62.2 and 65.9% for the nanofibers from RPB and STR after 500 cycles, respectively.

An overview of the magnetoresistance phenomenon in molecular systems.

In this review, the classification of magnetoresistance effects, the electrical conduction mechanisms without and with magnetic field, and the spintronics are briefly summarized. The magnetoresistance effect in the molecular systems including small organic molecules, carbon nanotubes, graphene, conductive polymers and their nanocomposites is critically reviewed. The four normally used models are elaborated to disclose the mechanisms of organic magnetoresistance (OMAR) in the organic systems. The most current applications of these molecular systems are also summarized. These molecular systems are envisioned to create next-generation spintronic and electronic devices for flexible applications.

Giant magnetoresistance in non-magnetic phosphoric acid doped polyaniline silicon nanocomposites with higher magnetic field sensing sensitivity.

Phosphoric acid doped conductive polyaniline (PANI) polymer nanocomposites (PNCs) reinforced with silicon nanopowders have been successfully synthesized using a facile surface initiated polymerization (SIP) method. The chemical structures of the nanocomposites are characterized using Fourier transform infrared (FT-IR) spectroscopy. The enhanced thermal stability of the silicon-PANI PNCs compared with pure PANI is obtained using thermogravimetric analysis (TGA). The obtained optical band gap of the PNCs using Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) decreases with increasing silicon loading. The dielectric properties of the PNCs are strongly related to the silicon loading level. Temperature dependent resistivity analysis reveals a quasi 3-D variable range hopping (VRH) electrical conduction mechanism for the synthesized PNCs. Room temperature giant magnetoresistance (GMR) is observed in the synthesized non-magnetic nanocomposites and analyzed using the wave-function shrinkage model.