Reversible Behavior Research Articles

Investigation of Grain Boundary Effects in Sm0.2Ce0.8O2-x Thin Film Memristors.

Cerium-based materials (CeO2-x) are of significant interest in the development of vacancy-modulated resistive switching (RS) memory devices. However, the influence of grain boundaries on the performance of memristors is very limited. To fill this gap, this study explores the influence of grain boundaries in cerium-based thin film resistive random-access memory (RRAM) devices. Sm0.2Ce0.8O2-x (SDC20) thin films were deposited on (100)-oriented Nb-doped SrTiO3 (NSTO) and (110)-oriented NSTO substrates using pulsed laser deposition (PLD). Devices constructed with a Pt/SDC20/NSTO structure exhibited reversible and stable bipolar resistive switching (RS) behavior. The differences in conduction mechanisms between single-crystal and polycrystalline devices were confirmed, with single-crystal devices displaying a larger resistance window and higher stability. Combining the results of XPS and I-V curve fitting, it was confirmed that defects near the grain boundaries in the SDC-based memristors capture electrons, thereby affecting the overall performance of the RRAM devices.

Effect of prior austenite grain size on austenite reversion, bainite transformation and mechanical properties of Fe-2Mn-0.2C steel

To elucidate the response of austenite reversion and subsequent bainite transformation behavior to the prior austenite grain (PAG) size, the transformation kinetics and amount of reverted austenite in the intercritical region, the subsequent bainite transformation kinetics, and the tensile properties were investigated by dilatometers, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and the mechanical tests. The results show that, when annealed at 730 °C, fine-grained specimens exhibit faster reverted austenite transformation rate than coarse-grained specimens due to the presence of more PAG boundaries. As the intercritical temperature rises to 760 °C, more intragranular globular austenite forms in the coarse-grained specimen, which accelerates the reverted austenite transformation rate. Compared to fine-grained specimens, coarse-grained specimens exhibit faster bainite transformation and higher amount of bainitic ferrite. The microstructure after austempering consists of intercritical ferrite, bainitic ferrite, RA and fresh martensite. With increasing the austempering time, more bainitic ferrite is formed and the amount of RA and fresh martensite decreases. With increasing the austempering time, the increase in the amount of bainitic ferrite leads to an increase in the yield strength, while the decrease in the amount of RA leads to a decrease in the elongation. Moreover, compared with coarse-grained specimens, the finer microstructure in fine-grained specimens improves yield and tensile strengths, while higher amount of RA contributes to larger uniform and total elongations.

Green Synthesis of Stable Lignin Nanoparticles with Reversible Swelling Behavior and Enhanced Multifunctional Features

Green Synthesis of Stable Lignin Nanoparticles with Reversible Swelling Behavior and Enhanced Multifunctional Features

High‐entropy configuration strategy boosts excellent rate performance of layered oxide for sodium‐ion batteries

AbstractLayered oxides are considered to be potential cathodes for sodium‐ion batteries based on high theoretical capacity and ease of synthesis. However, the complex phase transition caused by interlayer sliding in layered oxides leads to poor cycling stability, which will hinder their further application. Here, we designed a newly O3‐type layered cathode NaNi0.3Co0.2Cu0.1Mn0.2Ti0.2O2 based on high‐entropy to achieve highly reversible phase transition behavior. It reveals 132 mAh g−1 at 0.2 C within 2–4 V increasing the energy density to 408 Wh kg−1 and it shows an outstanding rate capability of 90 mAh g−1 at 80 C (84.90% capacity retention after 1,500 cycles at 80 C). In‐situ XRD shows that reasonable design of high‐entropy components in layered material can achieve the purpose of delaying the occurrence of phase transition and DFT calculations show that the introduction of Co in transition metal layers can effectively improve the rate performance of the material. This work is of great significance in guiding the design and synthesis of highly stable layered cathode materials for sodium‐ion batteries.

Water-Soluble Reversible Photo-Cross-Linking Polymer Dielectrics.

Effective recycling of mixed materials requires the separation of the different components without the need for toxic solvents. One approach involves utilizing a water-soluble coating with reversible photo-cross-linkers, making it robust until end of life where it can then be dissolved in water after de-cross-linking. Here, a novel coumarin methacrylate monomer and its nitroxide-mediated copolymerization to create poly((methacrylic acid)-co-(styrene sulfonate)-co-(coumarin methacrylate)) for water-soluble thin films are reported. Under exposure to light, the coumarin functional groups produce reversible [2+2] cycloadditions which cross-link the resulting polymer films, making them no longer water soluble. Characterization of reversible cross-linking behavior is reported through changes in contact angle and in situ rheological characterization. The resulting polymers are successfully integrated into metal-insulator-metal capacitors, demonstrating the potential use for water-soluble reversible photo-cross-linkable dielectric materials for organic electronics.

Tetraphenylethene-based mononuclear aggregation-induced emission (AIE)-active mechanofluorochromism gold(I) complexes with different auxiliary ligands

In this study, a series of tetraphenylethene-containing gold(I) complexes with different auxiliary ligands have been synthesized. These complexes were characterized using a variety of techniques including nuclear magnetic resonance spectroscopy, mass spectrometry, and single crystal X-ray diffraction. Their aggregation-induced emission (AIE) behaviors were investigated through ultraviolet/visible and photoluminescence spectrum analyses, and dynamic light scattering measurements. Meanwhile, their mechanofluorochromic properties were also studied via solid-state photoluminescence spectroscopy. Intriguingly, all these mononuclear gold(I) molecules functionalized by tetraphenylethene group demonstrated AIE phenomena. Furthermore, five gold(I) complexes possessing diverse auxiliary ligands exhibited distinct fluorescence changes in response to mechanical grinding. For luminogens 2–5, their solids showed reversible mechanofluorochromic behaviors triggered by the mutual transformation of crystalline and amorphous states, while for luminogen 1, blue-green-cyan three-color solid fluorescence conversion was realized by sequential mechanical grinding and solvent fumigation. Based on this stimuli-responsive tricolored fluorescence feature of 1, an information encryption system was successfully constructed.

Novel coumarin-based ratiometric bifunctional fluorescent probe mimicking a set-reset memorized device

A novel coumarin-based fluorescent sensor CHE, incorporating 2-hydrazinylbenzothiazole and coumarin aldehyde, has been developed that demonstrated a preferential detection of Hg2+ and Ag+ in presence of interferences. Compared to previously prevalent intensity-based fluorescent probes, CHE exhibited a ratiometric fluorescence response to Hg2+ and Ag+, and further accurately differentiated Hg2+ and Ag + using the differential extractive ability of EDTA when interacting with ion-CHE complexes. Sensing mechanism was investigated and elucidated. The chemosensor CHE was successfully applied to detect Hg2+ and Ag+ in six distinct samples with satisfactory results. Additionally, combinatorial logic circuits were constructed utilizing three distinct logic gates (NOT, OR, and INH) based on the sensor's differential output signals in response to Hg2+/Ag+ and other cations. Interestingly, utilizing the reversible and reproducible switching behavior of the EDTA interaction with Hg2+, a conceptual 'Write–Read–Erase–Read' memory function with multi-write capability was proposed, offering a novel perspective for molecular-based memory systems.

Light-Triggered Reversible Swelling of Azobenzene-Containing Block Copolymer Worms via Confined Deformation Prepared by Polymerization-Induced Self-Assembly.

Stimuli-responsive block copolymer nanoparticles (NPs) have received close attention in recent years owing to their tremendous application potential in smart materials. Azobenzene-containing NPs are widely studied due to the advantages of light as a stimulus and fast reversible trans-cis isomerization of azobenzene chromophores. However, the inefficient preparation process and difficult reversible transformation of morphologies limit their development. Herein it is demonstrated that the light-triggered reversible swelling behavior of wormlike NPs with high azobenzene content could be realized via confined deformation. These worms are prepared in large quantities via polymerization-induced self-assembly based on the copolymerization of 11-(4-(4-butylphenylazo)phenoxy)undecyl methacrylate (MAAz) and N-(methacryloxy)succinimide (NMAS) monomers. Upon UV/visible light irradiation, the reversible deformation of worms is achieved when the feed molar ratio of NMAS/MAAz is relatively high or via crosslinking using diamines, which leads to the reduction of the photoisomerization efficiency. The diameter variation of the worms is influenced by the amount and types of crosslinkers. Moreover, the scalability of this strategy is further proved by the fabrication of photo- and reductant-responsive crosslinked worms. It is expected that this study not only provides a new route to affording reversible photoresponsive NPs but also offers a unique insight into the reversible photodeformation mechanism of azobenzene-containing NPs.

Sulfato‐β‐cyclodextrin induced multivalent supramolecular directional aggregation of cyanovinylene derivatives for achieving reversible near‐infrared fluorescence

AbstractMolecular aggregation or supramolecular aggregation‐induced emission is one of the research hotspots in chemistry, biology, and materials. Herein, we report negatively charged sulfato‐β‐cyclodextrin (SCD) induced cyanovinylene derivatives (DPy‐6C) directional aggregation to form regular nanorods (DPy‐6C@SCD) through supramolecular multivalent interactions, not only achieves ultraviolet‐visible absorption redshifted from 453 to 521 nm but also displays near‐infrared (NIR) aggregation‐induced emission with a large spectral redshift of 135 nm. The DPy‐6C monomer presents random nanosheets with weak fluorescence but obtains regular aggregates after assembly with SCD through electrostatic interactions. In the presence of H+, the DPy‐6C@SCD can further aggregate into elliptical nanosheets without fluorescence changes due to the protonation of secondary amines. In contrast, the morphology of DPy‐6C@SCD becomes flexible and sticks together upon the addition of OH− with an emission blue shift of 72 nm and a 90‐fold intensity increase because of disrupting the stacking mode of aggregates, thereby achieving acid‐base regulated reversible fluorescence behaviors that cannot be realized by DPy‐6C monomer. The DPy‐6C@SCD can efficiently select the detection of volatile organic amines both in liquid and gas phases within 5 s at the nanomolar level. Taking advantage of RGB analysis and calculation formula application, the DPy‐6C@SCD has been successfully used to monitor various organic amines on a smartphone, accompanied by naked‐eye visible photoluminescence. Therefore, the present research provides an efficient directional aggregation method through supramolecular multivalent interactions, which not only realizes topological morphology transformation but also achieves reversible NIR luminescent molecular switch and high sensitivity organic amines fluorescent sensing devices.

Investigation of Tl‐Doped Silicon by Low‐Temperature Photoluminescence during Light‐Induced Degradation Treatments

Scientific progress is made in understanding photoluminescence (PL) lines in thallium‐doped silicon. Two PL lines called A and P, which appear after quenching, are found to exhibit irreversible as well as reversible behavior under the application of light‐induced degradation (LID) treatments. The reversible behavior is similar to changes of a P line in indium‐doped silicon due to LID treatments, which have led to the identification of this P line to be caused by an InSi‐Sii‐defect. By exploiting the metastability of defects from the ASi‐Sii category, the experimental findings of this study indicate that the underlying defect for the A and P line in thallium‐doped silicon is the TlSi‐Sii‐defect.

Terminal halogen-containing rod-like liquid crystals: Synthesis, self-assembly, photophysical and mechanochromism properties

Five series of cyanostilbene-based rod-like liquid crystals containing one different terminal atom (H, F, Cl, Br and I) at one end and one terminal aliphatic chain with different numbers of carbon atoms at the other end were reported by Suzuki coupling and Knoevenagel reactions. The influence of terminal halogen atoms and terminal chain length on the self-assembly, AIE behavior, temperature-dependent emission and mechanochromism behavior was explored by POM, DSC, XRD, SEM, absorption spectra and emission spectra. All the compounds are enantiotropic liquid crystals. The lowest non-halogen substituted homologue exhibited solo N phase, but the higher non-halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature. All the lowest halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature and all the higher homologues only exhibited SmA. The distinct mesogenic phase transition could be attributed to the intermolecular interaction produced by terminal halogen and the rigidity of the terminal aliphatic chain. All the non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom) exhibited AIE behaviors, whereas the iodinated compounds exhibited extremely weak emission in solution and aggregated states due to the heavy atoms effect. These compounds also exhibited distinct solid-state emission with blue or cyan fluorescence, which could be quenched by increasing temperature. The reversible mechanochromism behavior was also achieved in all the compounds. The mechanical force induced quench in emission in non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom), whereas enhancement in iodinated compounds. The reversible mechanochromism behavior endowed these compounds with potential applications in rewritable paper and anti-counterfeiting. The interesting properties in these liquid crystals would be attributed to the balance of the halogen-halogen interactions, heavy atom effect, steric-hindrance effect and chain length. These investigations would be helpful to understand the relationship between chemical structures and properties.

Photoinduced Multimodal Motions and Reversible Fluorescence Switching in an Elasto‐Plastic Crystal

AbstractMulti‐stimuli‐responsive materials have received widespread attention in the field of adaptive materials due to their ability to adapt to changes in the environment. However, fabricating multiple stimuli into a single component crystal still remains challenging. In this study, a polymorphic elasto‐plastic Schiff‐based crystal displaying morphology‐dependent photomechanical motions is designed and investigated. Both Form I and Form II of it exhibit dual plasticity and elasto‐plasticity along different facets, which is attributed to the slidable separating layers. Moreover, Form I retains its elastic bending ability even after being plastically twisted, owing to the well‐maintained strong π–π interactions, whereas Form II can not twist without fractures. In addition, the photomechanical motions of Form I including jumping, twisting to bending are realized by adjusting the crystal morphologies, while Form II is lacking in response to ultraviolet light irradiation. Theoretical calculation analysis reveals that lattice deformation induced by photoisomerization of Form I is the driving forces for crystal motions. Furthermore, reversible luminescence switching behaviors are realized in Form I and Form II upon acid‐base fumigation as well as heating. The synergistic multi‐stimuli‐responsive mode based on heat, acid, and solvent stimuli provides an alternative path for multi‐mode information encryption.

Development of a novel sensory material for rapid detection of mercury ions in various water sources: Solution and solid-state analysis

A xanthene propane nitrile-based sensor material was successfully prepared, and an attempt towards the preparation of polymer bead form was made for the sensitive or selective detection of mercury ions (Hg2+) in water. The sensor material in solution as well as in polymeric form showed amazing selectivity over other added metal ions with a naked eye color change, UV visible spectral and fluorescence spectral change, and a rapid and excellent color change from colorless to purple. The 1H NMR study exposed the probable binding site of the probe with the added mercury ion. In this study, the imine nitrogen and the C = O interact with the mercury ion, resulting in the ring opening of lactam with a vivid color change. The EDTA test was done to verify the reversible behavior of the probe and confirmed its reversibility by UV–visible and fluorescence spectral studies. The polymer bead made using this probe can be used as a tool for monitoring mercury ions in real time in different sources of water samples. The sensor molecule itself senses the mercury ion in its solid state by simple grinding and changes its color from pale yellow to deep purple. The sensor color change response is very rapid towards mercury detection, which is confirmed by the prepared test strip.

β-Cyclodextrin-Tethered Butein, a Greener Redox-Active Biomaterial for Electrochemical Enzymatic Sensing of Sialic Acid.

Biocompatible, industrially scalable, and opto/electrochemically active biomaterials are promising for biosensor platform design and application. Herein, cyclic oligosaccharide, β-cyclodextrin (BCD), is conjugated with Butein, a chalcone-type polyphenol, via dehydration reaction of the hydroxyl groups of BCD and the benzoyl ring of Butein. Functional group changes in the conjugated BCD-Butein were comprehensively studied using UV-visible absorbance, Fourier transform-infrared, and X-ray photoelectron spectroscopic techniques. The electrochemical characteristics of BCD-Butein were explored using cyclic voltammetry, showing the reversible redox behavior (2e-/2H+) attributed to the catecholic OH group of Butein. The BCD-Butein-modified electrode exhibits a surface-confined redox process (R2 = 0.99, Ipa and Ipc) at the interface, suitable for external mediatorless sensor studies. An enzymatic biomolecular sensor has been constructed using BCD-Butein-modified glassy carbon and a screen-printed electrode targeting sialic acid as the model clinical biomarker. With the enzyme sialic acid aldolase, BCD-Butein-modified substrate exhibited a selective conversion of sialic acid to N-acetyl-d-mannosamine and pyruvate, with a wide linear detection range (1-100 nM), the lowest detection limit of 0.2 nM, and a quantification limit of 0.69 nM, convenient for clinical threshold diagnosis.

Streamlined electrochemical harvesting of cobalt and nickel from soft cemented carbide scrap for superior supercapacitors

We propose a complete circular economy and sustainability model from soft cemented carbide scrap to supercapacitor application. An enhanced recovery of cobalt and nickel was observed when deep eutectic solvent was used. A comparative in-situ electrochemical deposition of the recovered metals was done on stainless steel (SS), SS/activated carbon (AC), and SS/AC/polyaniline (PANI). The optimization of electrochemical extraction was carried out by varying voltage, time, and temperature. The surface area and conductive polymer's electronic distribution contributed to different surface morphological deposition of specific metals on them. Unique fluffy particle deposition was observed on the surface as fine grain particles with uniform particle size within 1 µm. The fabricated supercapacitors showed the pseudocapacitance behaviour. The presence of metal oxide nanocomposite deposition as the active material is particularly pronounced in the SS/AC/PANI device due to the inclusion of PANI as an active material and its substantial contribution to pseudocapacitance. The higher charge-discharge time of SS/AC/PANI at the same current densities compared to SS/AC may be due to the above-mentioned additional contribution of PANI's quickly reversible redox behavior. Hence, the overall electrochemical extraction from scrap to supercapacitor will undoubtedly lead to achieving the sustainable development goals (SDGs)

Theoretical and experimental study on the trans-critical vibration reduction of flexible shafts by multi-gap limiting ring device considering rub-impact and dry friction

Abstract The flexible shafts in aviation equipment experience severe vibration upon exceeding the critical speed, causing severe damage to the equipment. To address this issue, a novel technique for vibration reduction using a multi-gap limiting ring device is proposed. The coupled effects of rub-impact, dry friction, and limiting are considered in a dynamic model for a multi-gap limiting ring device, and then the dynamic equation for the bending-torsional coupling of the flexible shaft with the limiting ring device is derived. Furthermore, the reverse whirl instability behavior of the shaft and the effect of various parameters on the damper performance are analyzed using a hybrid numerical method. Finally, experiments are conducted to verify the accuracy of the theoretical method. The findings show that the critical speed of the shaft rises due to the increased stiffness from the rub-impact between the limiting ring device and the shaft. The rub-impact point simultaneously causes bending-torsional coupling, which leads to torsional vibration of the shaft. Moreover, the rubbing gap, friction coefficient, preload force, and dry friction gap have a considerable impact on the limiting ring device's ability to reduce vibration. A poor choice of parameters can result in malfunctioning of the limiting ring device. Overall, this study can serve as an effective theoretical guide for the vibration reduction of flexible shafts.

Magnesium vs. sodium alginate as precursors of calcium alginate: Mechanical differences and advantages in the development of functional neuronal networks

Calcium alginate is one of the most widely employed matrices in regenerative medicine. A downside is its heterogeneity, due to the poorly controllable character of the gelation of sodium alginate (NaAlg), i.e. the commonly used alginate salt, with calcium. Here, we have used magnesium alginate (MgAlg) as an alternative precursor of calcium alginate. MgAlg coils, more compact and thus less entangled than those of NaAlg, allow for an easier diffusion of calcium ions, whereas Mg is exchanged with calcium more slowly than Na; this allows for the formation of a material (Ca(Mg)Alg) with a more reversible creep behaviour than Ca(Na)Alg, due to a more homogeneous – albeit lower - density of elastically active cross-links. We also show that Ca(Mg)Alg supports better than Ca(Na)Alg the network development and function of embedded (rat cortical) neurons: they show greater neurite extension and branching at 7 and 21 days (Tubb3 and Map2 immunofluorescence) and better neuronal network functional maturation / more robust and longer-lasting activity, probed by calcium imaging and microelectrode array electrophysiology. Overall, our results unveil the potential of MgAlg as bioactive biomaterial for enabling the formation of functional neuron-based tissue analogues.

Effect of reduced graphene oxide on vulcanization of polydimethylsiloxane composites

AbstractThis research aims to investigate the effect of reduced graphene oxide (rGO) on the kinetics of addition vulcanization in polydimethylsiloxane (PDMS) elastomers. For this purpose, the synthesis of graphene oxide (GO) and silane‐grafted GO followed by chemical reduction of particles was conducted to prepare rGOs with different surface chemistry. Particles were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, x‐ray diffraction, scanning electron microscopy, and energy‐dispersive x‐ray analysis. Composites of PDMS containing these particles were prepared by solution mixing, and vulcanization of composites was investigated using differential scanning calorimetry. Results showed that the rate and degree of vulcanization reaction increase up to a critical concentration of particles and then decrease afterward. This behavior was attributed to the catalytic effect of chemical groups on the surface of rGOs, whereas the reverse behavior above the critical concentration was correlated to the immobilization of trapped rubber in the network of particles. Grafting graphene oxide by a long alkyl‐chain silane covered these chemical groups, suppressed the catalytic effect, improved the dispersion of particles, and shifted the critical concentration lower. The critical concentration was correlated to the electrical percolation threshold of particles and confirmed by the solvent swelling method. It was also shown that rGO can itself act as the catalyst for the vulcanization of PDMS with no need for platinum. As the dynamic‐mechanical‐thermal analysis showed, the PDMS composites containing 0.75 wt% of particles did not vulcanize properly. However, composites containing fewer particles were vulcanized.Highlights Reduced graphene oxide affects additional vulcanization of PDMS. Below a critical loading, rGO accelerates vulcanization by a catalytic effect. Above critical loading, rGO decelerates vulcanization by a networking effect. Surface groups of rGO control catalytic and networking mechanisms. Silane modification of rGO affects interfacial behavior, thus critical loading.

Photocycloaddition of Zero-Dimensional Metal Halide Hybrids with Reversible Photochromism.

In this work, two zero-dimensional (0D) metal halide hybrids L2ZnBr4 [1, L = (E)-4-(2-(1H-pyrrol-3-yl)vinyl)-1-methylpyridin-1-ium] and L6Pb3Br12 (2) were prepared, which demonstrated photochromism and photoinduced cracking. Upon irradiation at 450 nm, a single crystal-to-single crystal transformation occurred as a result of the [2 + 2] photocycloaddition of L. Interestingly, compared to the complete photocycloaddition of L in 1, only two-thirds of L monomers could be photodimerized in 2 because of the difference in L orientation. 1 shows reversible photochromic behavior including rapid response time, few cracks, high conversion rate, and good reaction reversibility, while 2 exhibits no significant color change but distinct photoinduced cracking because of the large local lattice strain induced by inhomogeneous and anisotropic deformation. Moreover, the photocycloaddition of L results in the distinct shift of photoluminescence of 1 and 2, attributed to the variation in conjugation of π electrons and distortion of metal halide clusters. As a proof-of-concept, reversible optical writing is demonstrated for 1. These findings provide new insights into the design of stimuli-responsive multifunctional materials.

Reversible shape memory behavior of knitting-fabric reinforced polymer matrix composites

Reversible self-shaping behavior has been occurred with chemically crosslinked polymers and multi-layer structures while this behavior is difficultly realized for the fabric reinforced polymeric composites. In this work, a thin weft plain knitted fabric reinforced shape memory polymer composites (SMPCs) with reversible shape memory effect were developed. The effect of sizes, knitting densities and actuated temperatures on reversible shape memory behavior of SMPC was investigated. The results show that the maximum self-bending curvature of SMPCs is 35.8 m-1 and the shape recovery ratio reaches 82.2 %. A simplified finite element model was established to simulate and analyze the process of self-bending with heating and self-recovery with cooling of SMPC. Interestingly, the SMPC in wale direction (90°) has the inverse self-bending curvature of −18.4 m-1 as compared with that of SMPC in course direction (0°). The complex double curvature self-bending behavior of SMPC was also demonstrated. This work helps to broaden the development and research of reversible shape memory composites.