Reversible Variation Research Articles

Wettability of graphene: from influencing factors and reversible conversions to potential applications.

As a member of the carbon material family, graphene has long been the focus of research on account of its abundant excellent properties. Nevertheless, many previous research works have attached much importance to its mechanical capacity and electrical properties, and not to its surface wetting properties with respect to water. In this review, a series of methods are put forward for characterization of the water contact angle of graphene, such as experimental measurements, classic molecular dynamics simulations, and formula calculations. A series of factors that affect the wettability of graphene, including defects, controllable atmosphere, doping, and electric field, are also discussed in detail, and have rarely have been covered in other review articles before. Finally, with the developments of smart surfaces, a reversible wettability variation of graphene from hydrophobic to hydrophilic is important in the presence of external stimulation and is discussed in detail herein. It is anticipated that graphene could serve as a tunable wettability coating for further developments in electronic devices and brings a new perspective to the construction of smart material surfaces.

Preparation of Smart Poly(SPAA‐co‐MMA) Film Materials for Regulating Wettability and Humidity by Electrospinning

Smart photoresponsive structured films with tunable wettability and ambient humidity were developed from acrylamino spiropyran–methyl methacrylate copolymer by electrospinning in this work. The wettability of the electrospun materials and ambient humidity can be reversibly regulated by the simple change of UV–Vis light irradiation due to the photoisomerization mechanism of spiropyran chromophore. Under UV light irradiation, the spiropyran molecules exhibit a colored polar open‐ring status which is hydrophilic, whereas under visible light irradiation it is colorless, nonpolar, and hydrophobic. As a promising and efficient method to produce surfaces with appropriate roughness, electrospinning was used to control the morphology of the copolymer surface, and significantly it is found that the roughness of the surface can strongly influence the reversible variation range of the water contact angle and humidity. POLYM. ENG. SCI., 59:E279–E286, 2019. © 2018 Society of Plastics Engineers

Inkjet-printed metal oxide nanoparticles on elastomer for strain-adaptive transmissive electrochromic energy storage systems

ABSTRACTThe emergence of soft energy devices provides new possibilities for various applications, it also creates significant challenges in the selection of structural design and material compatibility. Herein, we demonstrate a stretchable transmissive electrochromic energy storage device by inkjet-printing single layer of WO3 nanoparticles on an elastomeric transparent conductor. Such hybrid electrode is highly conductive and deformable, making it an excellent candidate for the application: large optical modulation of 40%, fast switching speed (<4.5 s), high coloration efficiency (75.5 cm2 C−1), good stability and high specific capacity (32.3 mAh g−1 and 44.8 mAh cm−3). The device consists of WO3-based hybrid electrode and polyaniline/carbon nanotubes composite electrode. It maintains excellent electrochromic and energy storage performance even when stretched up to 50%, and achieves a maximum areal energy density of 0.61 μWh cm−2 and power density of 0.83 mW cm−2, which is one of the highest values in stretchable transparent energy storage devices. A device featuring stretchable transparent nanowires based electrode is illustrated as an energy indicator in which the stored energy can be monitored via reversible color variation. This high performance and multifunctional electrochromic energy storage device is a promising candidate for deformable and wearable electronics.

Local Control of Exchange Bias by Resistive Switching

The local modulation of exchange bias in resistive switching structure Co/CoOx/HfOx/Pt is reported, where CoOx/HfOx serves as the storage medium and Co behaves as the bottom (positive) electrode. The stack shows the exchange bias effect for the coupling at the Co/CoOx interface at the high resistance state. The formation of metallic Co or Co‐rich CoOx conductive filaments in the CoOx layer at the low resistance state leads to the bi‐hysteresis loops, reflecting the manipulation of exchange bias at local positions, where the formation of Co‐based filaments and the Co layer just below the filaments have no pinning effect. Besides, an oxidation–reduction process occurs in the Co layer, producing the reversible variation of saturated magnetization for the high/low resistance states. The electrochemical mechanism accounts for both local manipulation of exchange bias and changeable saturated magnetization. This work provides a different avenue for designable memories and magneto‐electric coupling devices.

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo, acetate, and halo ligands

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X⋅0.5H2O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN2O2X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.

Facile, rapid synthesis of N,P-dual-doped carbon dots as a label-free multifunctional nanosensor for Mn(VII) detection, temperature sensing and cellular imaging

We rapidly synthesized N,P-dual-doped carbon dots (N,P-CDs) via the acid-base neutralization spontaneous heat using a simple blend of phthalic acid, 1,2-ethylenediamine, and concentrated phosphoric acid. The approach is automatic without external heat treatment to speedily produce dozens of N,P-CDs, which refrain high temperature, sophisticated manipulations, and long reaction times. As-fabricated N,P-CDs with excellent luminescent properties, superior biocompatibility and respectable fluorescence quantum yield (QY) of 15% have been employed for the development of a label-free multifunctional fluorescence sensing platform for the detection of Mn(VII), temperature sensing and cellular imaging. Mn(VII) is able to effectively quench the fluorescence of N,P-CDs based on inner filter effect (IFE) because the absorption bands of Mn(VII) can perfectly overlap the emission and excitation wavelengths of N,P-CDs. The system had high selectivity toward Mn(VII) and the detection limit was 48.3 nM in the broad linear span from 10 μM to 200μM. Moreover, the N,P-CDs were extended for sensing Mn(VII) in living cell due to favorable biocompatibility and negligible cytotoxicity. Furthermore, the sensors showed a linear and reversible variation of emission intensity for a temperature range from 25℃ to 80℃, with a sensitivity of −1.79% per ℃. The practical implications of N,P-CDs for Mn(VII) detection have been demonstrated in Teas leaves and Medicinal herbs samples with satisfactory results.

Influence of environmental parameters on the seismic velocity changes in a clayey mudflow (Pont-Bourquin Landslide, Switzerland)

An earthflow/mudflow of a few thousand cubic metres occurred at the toe of the Pont-Bourquin Landslide (PBL, Swiss Alps) in late August 2010. This event was preceded by a drop of about 6% in surface wave velocity (dV/V) determined from ambient vibration records. A seismic monitoring system made of three pairs of sensors was re-installed across the transportation and accumulation zones of the landslide in October 2011, allowing daily relative changes in seismic velocity to be measured for a period of 4.5 years. No similar drop in dV/V was observed during this period, consistently with the lack of significant landslide acceleration or earthflow/mudflow events. However, the three dV/V time series showed periodic and reversible variations in a range − 2% to 2%, suggesting a probable influence of seasonal parameters. They were cross-correlated to daily environmental (temperature and rainfall) and surface displacement time series. In the long term (yearly scale), dV/V variations are mainly driven by the temperature with short delays (30 to 50 days) indicating that the shallow layer (first 2 m) controls the dV/V variations. In the short term, the landslide response to precipitations exhibits a small decrease in dV/V with a delay of 2 to 5 days, in contrast with the displacement rate that almost instantaneously responds to the rainfall. The continuous seismic monitoring of PBL using ambient vibrations has proved to be a robust method for getting information at depth, with no data gap even during winters. The seasonal reversible seismic velocity variations turned out to be in a range lower than the drop observed before the August 2010 earthflow/mudflow, highlighting the interest of incorporating the dV/V technique in monitoring systems.

Effects of dietary manipulation on compensatory growth of juvenile genetically improved farmed tilapia (Oreochromis niloticus).

A 40-day feeding trial was conducted to investigate whether feeding a low-protein diet (25%) once daily for either 10 (L10H30) or 20 (L20H20) days then re-feeding a high-protein diet (35%) thrice daily elicit compensatory growth (CG) in genetically improved farmed tilapia (GIFT), Oreochromis niloticus (11.02 ± 0.05g). Fish on the control treatment were fed 35% protein diet over 40days (H40). Fish were stocked into nine 100-L tanks (30 fish per tank) with 3 replicate tanks for each group. Growth performance, feed utilization, proximate composition of body compartment, serum biochemical parameters, and hepatopancreatic histology and expressions of some genes related to inflammatory cytokine were evaluated every 10days. Growth of L10H30 fish were similar to the control, whereas the weight of L20H20 fish were lower (P < 0.05) at day 20, but this significant difference disappeared at the end of the experiment. During 20-30days, specific growth rate and feed intake were significantly higher (P < 0.05) and feed efficiency was lower (P < 0.05) in L20H20 fish than those in H40 fish. Dietary manipulations did not affect (P > 0.05) viscerosomatic and hepatosomatic indices, condition factors, serum biochemical parameters, and hepatopancreatic histology. Significant differences (P < 0.05) in proximate composition were observed only in viscera and muscle between L20H20 fish and H40 fish at day 20. The mRNA expressions of heat shock protein 70kDa, tumor necrosis factor-α and interleukin (IL)-1β were higher (P < 0.05) in L10H30 and L20H20 fish at day 10, while IL-1β mRNA expression was lower (P < 0.05) in L20H20 fish at day 30 than those in H40 fish. Our results indicated that L20H20 fish elicited a complete CG and induced reversible physiological variations in juvenile GIFT.

Outdoor performance monitoring of perovskite solar cell mini-modules: Diurnal performance, observance of reversible degradation and variation with climatic performance

The outdoor performance monitoring of two types of perovskite solar cell (PSC) mini-modules based on two different absorbers - CH3NH3PbI3 (MAPI) and Cs0.05FA0.83MA0.17PbI(0.87Br0.13)3 (FMC) is reported. PSC modules displayed markedly different outdoor performance characteristics to other PV technologies owing to the reversible diurnal changes in efficiency, difference in temperature coefficient between absorber layers and response under low light conditions. Examination of diurnal performance parameters on a sunny day showed that whereas the FMC modules maintained their efficiency throughout the day, the MAPI modules peaked in performance during the morning and afternoon, with a strong decrease around midday. Overall, the MAPI modules showed a strongly negative temperature coefficient (TC) for PCE, whereas the FMC modules showed a moderate positive temperature coefficient performance as a function of temperature due to the increase in JSC and FF. Outdoor monitoring of the MAPI modules over several days highlighted that the reduced over the course of the day but recovered overnight. In contrast the FMC modules improved slightly during the daytime although this was too reversed overnight. This paper provides insight into how PSC modules perform under real-life conditions and consider some of the unique characteristics that are observed in this solar cell technology.

Stretchable Optomechanical Fiber Sensors for Pressure Determination in Compressive Medical Textiles.

Medical textiles are widely used to exert pressure on human tissues during treatment of post-surgical hematoma, burn-related wounds, chronic venous ulceration, and other maladies. However, the inability to dynamically sense and adjust the applied pressure often leads to suboptimal pressure application, prolonging treatment or resulting in poor patient outcomes. Here, a simple strategy for measuring sub-bandage pressure by integrating stretchable optomechanical fibers into elastic bandages is demonstrated. Specifically, these fibers possess an elastomeric photonic multilayer cladding that surrounds an extruded stretchable core filament. They can sustain repetitive strains of over 100%, and respond to deformation with a predictable and reversible color variation. Integrated into elastic textiles, which apply pressure as a function of their strain, these fibers can provide instantaneous and localized pressure feedback. These colorimetric fiber sensors are well suited for medical textiles, athletic apparel, and other smart wearable technologies, especially when repetitive, large deformations are required.

Reversible Negative Resistive Switching in an Individual Fe@Al2O3 Hybrid Nanotube for Nonvolatile Memory.

Hybrid nanostructures can show enormous potential in different areas because of their unique structural configurations. Herein, Fe@Al2O3 hybrid nanotubes are constructed via a homogeneous coprecipitation method followed by subsequent annealing in a reducing atmosphere. The introduction of zero band gap Fe nanocrystals in the wall of ultrawide band gap Al2O3 insulator nanotubes results in the formation of charge trap centers, and correspondingly a single hybrid nanotube-based two-terminal device can show reversible negative resistive switching (RS) characteristics with symmetrical negative differential resistance (NDR) at relatively high operation bias voltages. At a large bias voltage, holes and electrons can be injected into traps at two ends from electrodes, respectively, and then captured. The bias voltage dependence of asymmetrical filling of charges can lead to a reversible variation of built-in electromotive force, and therefore the symmetrical negative RS with NDR arises from two reversible back-to-back series bipolar RS. At a low readout voltage, the single Fe@Al2O3 hybrid nanotube can show an excellent nonvolatile memory feature with a relatively large switching ratio of ∼30. The bias-governed reversible negative RS with superior stability, reversibility, nondestructive readout, and remarkable cycle performance makes it a potential candidate in next-generation erasable nonvolatile resistive random access memories.

Transition of Magnetic Field Due to Geometry of Magneto-Active Elastomer Microactuator With Nonlinear Deformation

Magneto-active elastomer is widely used for microactuator/microsensor application. For optimization of the actuation performance of the magneto-active elastomer, it is crucial to characterize its magnetic field distribution and mechanical behavior. By a novel multiphysics model, this paper thus investigates the transition between the uniform and non-uniform magnetic fields and the field-induced nonlinear deformation, due to reversible variation of the geometric size of the magneto-active elastomer from infinite to finite one. In this paper, both the elastomer and its surrounding medium are covered in the computational domain, where the Maxwell stress over the elastomer-surrounding interface is considered as an additional mechanical boundary, and the nonlinear magnetization included in a proposed free energy density. After validation of the present model with both the published theoretical and experimental works, it is concluded that increasing the geometric size of the magneto-active elastomer leads to a more uniform magnetic field, and thus the elastomer undergoes the transition from the non-uniform to uniform magnetic fields, if its size increases to a critical point, such as aspect ratio of 12.4 for the present cylindrical magneto-active elastomer. [2017-0232]

Electrochemical promotion of nanodispersed Ru-Co catalysts for the hydrogenation of CO2

Electrochemical promotion of the CO2 hydrogenation to CH4 and CO on a nanodispersed Ru-Co catalyst has been achieved via slurry deposition of the nanodispersed catalyst on an interlayer Ru film deposited on a BZY (BaZr0.85Y0.15O3) proton conducting solid electrolyte disc. The effect of current is nonFaradaic, with Faradaic efficiency values as high as 60 and leads to a reversible variation of the selectivity to CH4 between 16% and 41%. Due to thermal spillover of protons on the Ru-Co catalyst surface, the open circuit selectivity to CO is quite high, i.e. up to 84% and similar values are obtained via negative potential application, i.e. proton supply to the Ru catalyst film deposited on BZY before the deposition of the nanodispersed catalyst. These results underline the similarity between electrochemical promotion and metal support interactions when using proton conducting supports. They also show the usefulness of electrochemical promotion for mechanistic investigations. The electrochemical promotion of nanodispersed catalysts is a promising step for the practical utilization of electrochemical promotion.

Efficient synthesis of tungsten oxide hydrate-based nanocomposites for applications in bifunctional electrochromic-energy storage devices

In this work, we realized the large-scale synthesis of WO3 · H2O nanoflakes (NFs), g-C3N4/WO3 · H2O nanocomposite (NC) and graphene (G)/WO3 · H2O NC via a sonochemical process with tungsten salt as the precursor, g-C3N4 or G sheets as the supports, and distilled water as the solvent. Both the g-C3N4/WO3 · H2O NC and G/WO3 · H2O NC exhibited much better electrochromic (EC) performance (higher coloration efficiencies and faster response times) than that of the WO3 · H2O NFs. Using the WO3 · H2O-based materials as electrode materials, EC batteries that integrate the energy storage and EC functions in one device have been assembled. The energy status of the EC batteries could be visually indicated by the reversible color variations. Compared with the plain WO3 · H2O-based EC batteries, the NC-based EC batteries possessed a lower color contrast between the charged and discharged conditions but much longer discharge durations. The EC batteries could be quickly charged in a few seconds by adding H2O2, and the charged batteries exhibited significantly-enhanced discharging durations in comparison with the initial ones. The g-C3N4/WO3 · H2O NC-EC batteries charged by a small amount of H2O2 could produce a long discharging duration up to 760 min.

Reduction and oxidation annealing effects on Cu K-edge XAFS for electron-doped cuprate superconductors

Reduction and oxidation annealing effects on the electronic states around the copper sites for Pr2-xCexCuO4 and Nd2-xCexCuO4 with x = 0 and x = 0.15 were investigated by Cu K-edge x-ray absorption measurements. Cu K near-edge spectra were changed by the reduction annealing in a manner similar to the case of Ce substitution for both x = 0 and x = 0.15. This means an increase of electron density at the copper sites, indicating the aspect of electron doping in the reduction annealing. This reduction annealing effect on the near-edge spectra are reverted by the additional oxidation annealing. The amount of electron density around the copper sites is varied by the reduction and oxidation annealing, reversibly, corresponding to the reversible variation of the physical property from insulating to superconductivity.

Numerical prediction of circular tunnel seismic behaviour using hypoplastic soil constitutive model

Numerical simulation of the centrifuge experiment with dynamic loading on a small scale circular tunnel model surrounded by dry Buzzard sand is being presented. Considering soil dynamic behaviour properly, analyses were performed using an advanced hypoplastic constitutive model for sands considering the intergranular strain. The results include: settlement, lining forces time histories and peak acceleration in normalized model depth, were in good agreement with experimental data. Additional numerical modelling have been performed using hardening soil model with small-strain stiffness (HSS) and Mohr–Coulomb criteria (MC), then the results compared in detail with the hypoplastic (HP) model. The finite element predictions of settlement time histories and the internal forces mobilized in the tunnel lining were compared and the results declared that although settlements were underestimated by all models, HP has shown better responses in following the experimental trend. Also, internal forces obtained by the HP model showed smaller reversible variations.

Microfluidic preparation of flexible micro-grippers with precise delivery function.

We used microfluidic technology for preparing gas-liquid Janus emulsions; we firstly proposed a one-step preparation method of micro-grippers and then characterized the function of oriented and precise delivery behavior. Because of the enrichment of Fe3O4 nanoparticles, the micro-gripper can reach a speed of 1.5 mm s-1 driven by a magnetic field. The micro-gripper's body is made of a poly(N-isopropylacrylamide) hydrogel, a reversible temperature-responsive polymer. The thermo-sensitivity of hydrogels offers the function of grasping, to closely integrate with the target carried, ensuring the stability of the carrying process. The reversible variation of the hydrogel allows the micro-gripper to be reusable and have a long shelf life.

Electricity on Rubber Surfaces: A New Energy Conversion Effect.

This work describes the conversion of mechanical energy to electricity, by periodically stretching rubber tubing and allowing it to relax. The rubber surface shows periodic and reversible electrostatic potential variations, in phase with the tubing length. The potential change depends on the elastomer used: silicone loses charge when stretched and becomes strongly negative when relaxed, whereas the stretched natural rubber is positive, becoming negative when relaxed. Every other elastomeric material that was tested also showed periodic potential but followed different patterns. When the motion stops, the potential on the resting samples decreases quickly to zero. The potential oscillation amplitude decreases when the relative humidity decreases from 65 to 27%, but it is negligible when the rubber tubing is previously swollen with water or paraffin oil. Elastomer charging patterns do not present the well-known characteristics of piezo-, flexo-, or triboelectricity, and they are discussed considering rubber rheology, wear, and surface properties, including the possibility of surface piezoelectricity. The following mechanism is suggested: rubber stretching provokes chemical and morphology changes in its surface, followed by a change in the surface concentration of H+ and OH– ions adsorbed along with water. The possibility of the occurrence of similar variations in other systems (both inert and biological) is discussed, together with its implications for energy scavenging from the environment.

Structural and Conformational Chemistry from Electrochemical Molecular Machines. Replicating Biological Functions. A Review.

Each constitutive chain of a conducting polymer electrode acts as a reversible multi-step electrochemical molecular motor: reversible reactions drive reversible conformational movements of the chain. The reaction-driven cooperative actuation of those molecular machines generates, or destroys, inside the film the free volume required to lodge/expel balancing counterions and solvent: reactions drive reversible film volume variations, which basic structural components are here identified and quantified from electrochemical responses. The content of the reactive dense gel (chemical molecular machines, ions and water) mimics that of the intracellular matrix in living functional cells. Reaction-driven properties (composition-dependent properties) and devices replicate biological functions and organs. An emerging technological world of soft, wet, reaction-driven, multifunctional and biomimetic devices and the concomitant zoomorphic or anthropomorphic robots is presented.

Novel preparation of ITO nanocrystalline films with plasmon electrochromic properties by the sol-gel method using benzoylacetone as a chemical modifier

In this paper, benzoylacetone (BzAcH) was introduced as a chelating agent to the sol-gel technique to fabricate indium tin oxide (ITO) nanocrystalline films. BzAcH was found to decrease the grain size of the ITO film, and the growth of ITO nanocrystals was controlled by varying the BzAcH content. ITO nanocrystalline films prepared by this method showed significant localized surface plasmon resonance (LSPR) absorption features that could be manipulated electrically by electrochemical doping. Plasmonic electrochromism realized in ITO films indicated a strongly reversible and persistent variation of the film transmittance in the near-infrared region (NIR). Furthermore, the plasmon electrochromic mechanism of ITO nanocrystals is discussed in this paper.