Tough and Strain-Sensitive Organohydrogels Based on MXene and PEDOT/PSS and Their Effects on Mechanical Properties and Strain-Sensing Performance.

Conductive hydrogels have shown promising application prospects in the field of flexible sensors, but they often suffer from poor mechanical properties, low sensitivity, and lack of frost resistance. Herein, we report a tough, highly sensitive, and antifreeze strain sensor assembled from a conductive organohydrogel composed of a dual-cross-linked polyacrylamide and poly(vinyl alcohol) (PVA) network, as well as MXene nanosheets as nanofillers and poly(3,4-ethylenedioxythiophene)-doped poly(styrenesulfonate) (PEDOT/PSS) as the main conducting component (PPMP-OH organohydrogel). The tensile strength and toughness of PPMP-OH had been greatly enhanced by MXene nanosheets due to the mechanical reinforcement of MXene nanosheets, as well as various strong noncovalent interactions formed in the organohydrogels. The PPM1P-OH organohydrogels showed a tensile strength of 1.48 MPa at 772% and a toughness of 5.59 MJ/m3. Moreover, the conductivity and strain-sensing performance of PPMP-OH were significantly improved by PEDOT/PSS, which can form hydrogen bonds with PVA and electrostatic interactions with MXene. This was greatly beneficial for constructing a uniformly distributed and stable 3D conductive network and helped to obtain strain-dependent resistance of PPMP-OH. The strain sensors assembled from PPMP1-OH exhibited a high sensitivity of 5.16, a wide range of detectable strains up to 500%, and a short response time of 122 ms, which can effectively detect various physiological activities of the human body with high stability. In addition, the corresponding pressure sensor array also showed high sensitivity in identifying pressure magnitude and position.

Highly conductive and tough polyacrylamide/sodium alginate hydrogel with uniformly distributed polypyrrole nanospheres for wearable strain sensors.

Conductive hydrogels have attracted widespread attention because of their integrated characteristics of being stretchable, deformable, adhesive, self-healable, and conductive. Herein, we report a highly conductive and tough double-network hydrogel based on a double cross-linked polyacrylamide (PAAM) and sodium alginate (SA) network with conducting polypyrrole nanospheres (PPy NSs) uniformly distributed in the network (PAAM-SA-PPy NSs). SA was employed as a soft template for synthesis of PPy NSs and distribution of PPy NSs uniformly in the hydrogel matrix to construct SA-PPy conductive network. The PAAM-SA-PPy NS hydrogel exhibited both high electrical conductivity (6.44 S/m) and excellent mechanical properties (tensile strength of 560 kPa at 870 %), as along as high toughness, high biocompatibility, good self-healing and adhesion properties. The assembled strain sensors showed high sensitivity and a wide sensing range (a gauge factor of 1.89 for 0-400 % strain and 4.53 for 400-800 % strain, respectively), as well as fast responsiveness and reliable stability. When used as a wearable strain sensor, it was able to monitor a series of physical signals from human large-scale joint motions and subtle muscle movements. This work provides a new strategy for the development of electronic skins and flexible strain sensors.

A facile one-step approach for the fabrication of polypyrrole nanowire/carbon fiber hybrid electrodes for flexible high performance solid-state supercapacitors.

Wearable electronics are in high demand, requiring that all the components are flexible. Here we report a facile approach for the fabrication of flexible polypyrrole nanowire (NPPy)/carbon fiber (CF) hybrid electrodes with high electrochemical activity using a low-cost, one-step electrodeposition method. The structure of the NPPy/CF electrodes can be easily controlled by the applied electrical potential and electrodeposition time. Our NPPy/CF-based electrodes showed high flexibility, conductivity, and stability, making them ideal for flexible all-solid-state fiber supercapacitors. The resulting NPPy/CF-based supercapacitors provided a high specific capacitance of 148.4 F g-1 at 0.128 A g-1, which is much higher than for supercapacitors based on polypyrrole film/CF (38.3 F g-1) and pure CF (0.6 F g-1) under the same conditions. The NPPy/CF-based supercapacitors also showed high bending and cycling stability, retaining 84% of the initial capacitance after 500 bending cycles, and 91% of the initial capacitance after 5000 charge/discharge cycles.

The consortium of heterogeneous cobalt phthalocyanine catalyst and bicarbonate ion as a novel platform for contaminants elimination based on peroxymonosulfate activation.

The design of catalytic oxidation processes with high efficiency has attracted considerable attention for a long while in environmental catalysis. In this work, a novel oxidation system, CFs-CoPc/PMS, was developed by coupling cellulosic fibers-bonded cobalt phthalocyanine (CFs-CoPc) with peroxymonosulfate (PMS). CFs-CoPc/PMS system could effectively decolorize azo dyes such as Acid Red 1 (AR1) with almost 100% decolorization efficiency in 35 min, suggesting that the CFs-CoPc/PMS system was a highly efficient oxidation process. In addition, bicarbonate ion (HCO3(-)) was further introduced to CFs-CoPc/PMS to construct a combined system, CFs-CoPc/PMS/HCO3(-). Remarkably, this system turned the negative effect of HCO3(-) observed in most reported Co/PMS systems into a positive one, which enhanced the AR1 decolorization with over 2-fold increase of the rate constant. The main factor responsible for the enhancement was high-valent cobalt-oxo intermediates (PcCo(IV)=O), which was presumably generated via the heterolytic cleavage of the PMS OO bond by CoPc-HCO3(-) complex. It is noteworthy that high-valent cobalt-oxo intermediates as the major active species is different from most reported mechanisms in Co/PMS systems, in which hydroxyl and sulfate radicals are recognized as the dominant active species. This study paves an avenue for developing highly efficient catalytic oxidation technology for wastewater remediation.

Extremely enhanced contaminant decomposition catalyzed by hemin via the coupling of persistent free radicals and ascorbic acid.

Persistent free radicals (PFRs) have mainly been reported as negative species. Here we report a positive role of PFRs in enhancing reactive oxygen species (ROS) generation for an extreme rate enhancement in environmental pollutant decomposition.

Chromatic polydiacetylene with novel sensitivity.

Conjugated polymers have been investigated for a number of applications in optoelectronics and sensing due to their important electronic and optical properties. For instance, polydiacetylene (PDA) may change color in response to external stimuli and has been extensively explored as a material for chromatic sensors. However, the practical applications of PDA materials have been largely hampered by their irreversible chromatic transitions under limited stimuli such as temperature, pH, and chemical. As a result, much effort has been paid to improve the chromatic reversibility and increase the scope of external stimuli for PDA. In this tutorial review, the recent development of PDA materials which show reversible chromatic transition and respond to new stimuli including light and electrical current has been described.

UV-induced chromatism of polydiacetylenic assemblies.

Highly ordered lamellar polydiacetylene nanocomposites are synthesized by assembling polydiacetylene and azobenzene through a ready solution process. The trans-to-cis transition of azobenzene under UV light induces a conformational change of polydiacetylene with a color change from blue to red.

Stimuli-sensitive assemblies of homopolymers.

Two homopolymers assemble into nanoparitcles in a common solvent of water through ionic complexation. These nanoparticles reversibly and rapidly respond to both pH and temperature, and are particularly promising as intelligent systems.

Nanowire-based polypyrrole hierarchical structures synthesized by a two-step electrochemical method.

A simple two-step electrochemical method is proposed for the synthesis of nanowire-based polypyrrole hierarchical structures. In the first step, microstructured polypyrrole films are prepared by electropolymerization. Then, polypyrrole nanowires are electrodeposited on the surface of the as-synthesized microstructured polypyrrole films. As a result, hierarchical structures of polypyrrole nanowires on polypyrrole microstructures are obtained. The surface wettabilities of the resulting nanowire-based polypyrrole hierarchical structures are examined. It is expected that this two-step method can be developed into a versatile route to produce nanowire-based polypyrrole hierarchical structures with different morphologies and surface properties.