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Electroreduction of nitrate (NO3−) has emerged as a promising strategy for producing ammonia (NH3) at room temperature in recent years. However, the formation of the less electron-consuming H2 byproduct seriously limits the conversion efficiency of NO3− to NH3. In this study, we identify that N-doped Co3O4 can effectively convert NO3− to NH3 with a high performance (NH3 yield rate: 7.18 ± 0.59 mg h−1 cm−2, faradaic efficiency: 96.7 ± 0.88%), which is significantly higher than that of pure Co3O4 (NH3 yield rate: 4.95 ± 0.54 mg h−1 cm−2) and most reported Co-based catalysts (Table S1, ESI). Density functional theory (DFT) calculations coupled with X-ray absorption near-edge structure (XANES) experiments reveal that N-doping in Co3O4 releases more positive charge on the Co atom site due to charge compensation. This oxidized Co atom site enhances the adsorption of NO3− while weakening the adsorption of H+ through Coulombic interactions, thus improving NO3RR activity. Overall, our study provides an efficient electrocatalyst to avoid the formation of the H2 byproduct to facilitate the conversion of NO3− to NH3, and opens new avenues towards achieving green ammonia production by controlling Coulombic interactions. [ABSTRACT FROM AUTHOR]

The estimation of coherent signals in electromagnetic (EM) environments is constrained by a small number of snapshots and low signal-to-noise ratio (SNR). This paper presents an improved off-grid direction of arrival (DOA) estimation algorithm based on sparse Bayesian learning. The algorithm aims to enhance the accuracy of DOA estimation for coherent signals in EM environments with a small number of snapshots and a low SNR. The algorithm first employs a novel dimensionality reduction technique based on singular value decomposition (SVD) to construct a sparse signal representation model. Then, based on sparse Bayesian theory, the expectation–maximization algorithm is used to optimize parameters such as quantization error, noise power, and signal power, thereby improving DOA estimation accuracy. Simulation results demonstrate that, compared to subspace-based and on-grid direction-finding methods, the proposed algorithm achieves higher DOA estimation accuracy under conditions of low SNR, a small number of snapshots, and high signal correlation. Specifically, when the SNR exceeds − 4 dB, the root mean square error of the proposed algorithm is less than 2° in scenarios with a small number of snapshots. Additionally, when the SNR is greater than − 6 dB, the algorithm achieves a direction-finding success rate of over 90%. Furthermore, the algorithm maintains high performance even with correlated and fully coherent signals, demonstrating robustness to variations in the correlation coefficient. [ABSTRACT FROM AUTHOR]

The estimation of coherent signals in electromagnetic (EM) environments is constrained by a small number of snapshots and low signal-to-noise ratio (SNR). This paper presents an improved off-grid direction of arrival (DOA) estimation algorithm based on sparse Bayesian learning. The algorithm aims to enhance the accuracy of DOA estimation for coherent signals in EM environments with a small number of snapshots and a low SNR. The algorithm first employs a novel dimensionality reduction technique based on singular value decomposition (SVD) to construct a sparse signal representation model. Then, based on sparse Bayesian theory, the expectation–maximization algorithm is used to optimize parameters such as quantization error, noise power, and signal power, thereby improving DOA estimation accuracy. Simulation results demonstrate that, compared to subspace-based and on-grid direction-finding methods, the proposed algorithm achieves higher DOA estimation accuracy under conditions of low SNR, a small number of snapshots, and high signal correlation. Specifically, when the SNR exceeds − 4 dB, the root mean square error of the proposed algorithm is less than 2° in scenarios with a small number of snapshots. Additionally, when the SNR is greater than − 6 dB, the algorithm achieves a direction-finding success rate of over 90%. Furthermore, the algorithm maintains high performance even with correlated and fully coherent signals, demonstrating robustness to variations in the correlation coefficient. [ABSTRACT FROM AUTHOR]

LED packaging miniaturization has raised more requirements for LED materials. As a material contacting the LED chip directly, the reliability of LED non-conductive adhesive has also garnered increasing attention. This study optimized the formula for non-conductive adhesives for an imidazole curing system. The optimized composition of the adhesive is 25%wt for the curing agent and 30%wt for the silica. The prepared non-conductive adhesive has a 7-day pot life and 9-month storage stability. The shear strength reached 87 g and 72 g at 25 °C and 160 °C, respectively. The reliability of the LED modules packaged with the non-conductive adhesive was researched. The green and blue light intensity change was 4.7%, 43.7%, respectively, indicating good anti-aging properties. The blue light decay was mainly due to adhesive aging. The non-conductive adhesive effectively prevented "caterpillar" growth. This provides useful and practical guidelines for industry for applications of adhesive in different packages. [ABSTRACT FROM AUTHOR]

Ionically conducting eutectogels have gained popularity as temperature-tolerant and cost-effective substitutes for hydrogels and ionogels in flexible electronic devices. In this study, mechanically robust eutectogels with antibacterial properties were fabricated using a facile one-step process that relied solely on the physical entanglement of polymer chains. At low initiator concentrations, the vinyl monomers underwent radical polymerization in deep eutectic solvents (DESs), forming physically entangled and transparent eutectogels. The eutectogels exhibited excellent mechanical properties (tensile strength, elongation at break, and fracture energy of 8.04 MPa, 620.5%, and 28.69 ± 2.23 MJ m−3, respectively), a strong adhesion force, excellent ionic conductivity (0.43 ± 0.07 S m−1), and remarkable resistance to freezing and drying (−20 to 80 °C). Moreover, the eutectogels possessed superior self-healing abilities at room temperature without the need for external stimuli. As sensors, the fabricated eutectogels exhibited high sensitivity, thereby enabling the precise, real-time, and stable monitoring of human activities. The eutectogels have promising applications in wearable technology, healthcare devices, and human–computer interfaces. [ABSTRACT FROM AUTHOR]

The development of high-performance electromagnetic interference (EMI) shielding materials that minimize reflection is of paramount importance in the electronics industry. This study introduces a novel approach to fabricating multilayered composite films consisting of MXene and Fe3O4 nanosheets (FONS), which exhibit significantly enhanced EMI shielding effectiveness (SE) with reduced reflection characteristics. By leveraging the synergistic properties of highly conductive MXene and the magnetic properties of FONS, the composite films demonstrate a maximum SE of 34.3 dB within the X-band with a mere 0.17 mm thickness and a low filler content of 6.25 wt.%. The FONS contribute to an increased total EMI SE while concurrently suppressing the reflection SE, achieving a minimum reflection of only 4.2 dB. The alternating multilayered structure, characterized by dense distribution of MXene and the impedance matching capabilities of FONS/waterborne polyurethane layers, results in a pronounced interfacial polarization effect, which enhances the polarization loss. [ABSTRACT FROM AUTHOR]

In the realm of electromagnetic wave absorption materials, achieving a combination of broad absorption bandwidth, high absorption intensity, and practical versatility presents both a scientific challenge and an engineering necessity. This study introduces a lightweight, high compressibility poly-(methacrylimide) (PMI) composite foam with enhanced electromagnetic wave absorption properties. The multiwalled carbon nanotubes (MWCNT) and PMI were composited by ultraviolet (UV) photoinitiation prepolymerization, afterward combining the copolymerization curable-hot air method to prepare MWCNT/PMI composite foam. The resulting MWCNT/PMI composite foam with a minimal MWCNT content of less than 4.0 wt % exhibits a remarkable reflection loss of −55.0 dB and an extensive effective absorption bandwidth of 16.0 GHz within the 2–18 GHz range, attributable to its optimized porous structure and elevated dielectric loss. The complete frequency range of 2–18 GHz can be efficiently absorbed by MWCNT/PMI composite foam, making it ideal for broadband wave absorption. Additionally, composite foams all satisfy the requirements for lightweight design and high strength of microwave-absorbing materials due to its lightweight, good compressive strength, and heat resistance, making it more competitive in engineering applications. [ABSTRACT FROM AUTHOR]

Electroreduction of nitric oxide (NO) to NH3 (NORR) has gained extensive attention for the sake of low carbon emission and air pollutant treatment. Unfortunately, NORR is greatly hindered by its sluggish kinetics, especially under low concentrations of NO. Herein, we developed a chlorine (Cl) vacancy strategy to overcome this limitation over FeOCl nanosheets (FeOCl‐VCl). Density functional theory (DFT) calculations revealed that the Cl vacancy resulted in defective Fe with sharp d‐states characteristics in FeOCl‐VCl to enhance the absorption and activation of NO. In situ X‐ray absorption near‐edge structure (XANES) and attenuated total reflection‐infrared spectroscopy (ATR‐IR) verified the lower average oxidation state of defective Fe to enhance the electron transfer for NO adsorption/activation and facilitate the generation of key NHO and NHx intermediates. As a result, the FeOCl‐VCl exhibited superior NORR activities with the NH3 Faradaic efficiency up to 91.1 % while maintaining a high NH3 yield rate of 455.4 μg cm−2 h−1 under 1.0 vol % NO concentration, competitive with those of previously reported literatures under higher NO concentration. Further, the assembled Zn‐NO battery utilizing FeOCl‐VCl as cathode delivered a record peak power density of 6.2 mW cm−2, offering a new route for simultaneous NO removal, NH3 production, and energy supply. [ABSTRACT FROM AUTHOR]

Electroreduction of nitric oxide (NO) to NH3 (NORR) has gained extensive attention for the sake of low carbon emission and air pollutant treatment. Unfortunately, NORR is greatly hindered by its sluggish kinetics, especially under low concentrations of NO. Herein, we developed a chlorine (Cl) vacancy strategy to overcome this limitation over FeOCl nanosheets (FeOCl‐VCl). Density functional theory (DFT) calculations revealed that the Cl vacancy resulted in defective Fe with sharp d‐states characteristics in FeOCl‐VCl to enhance the absorption and activation of NO. In situ X‐ray absorption near‐edge structure (XANES) and attenuated total reflection‐infrared spectroscopy (ATR‐IR) verified the lower average oxidation state of defective Fe to enhance the electron transfer for NO adsorption/activation and facilitate the generation of key NHO and NHx intermediates. As a result, the FeOCl‐VCl exhibited superior NORR activities with the NH3 Faradaic efficiency up to 91.1 % while maintaining a high NH3 yield rate of 455.4 μg cm−2 h−1 under 1.0 vol % NO concentration, competitive with those of previously reported literatures under higher NO concentration. Further, the assembled Zn‐NO battery utilizing FeOCl‐VCl as cathode delivered a record peak power density of 6.2 mW cm−2, offering a new route for simultaneous NO removal, NH3 production, and energy supply. [ABSTRACT FROM AUTHOR]

The effect of the presence of a silane coupling agent containing different functional groups on the reaction kinetics and physical properties of epoxy resin generated via cationic thermopolymerization was investigated. The kinetics of cationic polymerization of epoxy resin was studied using a nonisothermal DSC method. The polymerization is propagated by activated chain end (ACE) and activated monomer (AM) processes. With an increase in silane content, the ACE apparent activation energy first decreased and then increased, while the AM apparent activation energy increased. Moreover, the shear strength, coefficient of linear thermal expansion, gelation time, environmental testing of damp heat, and steady state with varied contents of silane coupling agents were evaluated. The results indicated that the presence of a silane coupling agent has more adhesion and lower water absorption than pure EP. The coefficient of linear thermal expansion and gelation time increased with the increase in silane content, while the water absorption decreased with the increase in silane content. Comparing the overall performance of three silane coupling agents used in the research, the curing system obtained by blending with vinyltrimethoxysliane (VTS) is a much better option for practical application as an adhesive. [ABSTRACT FROM AUTHOR]

Field grading composites showing nonlinear conductive performance are usually applied to protection for electrical systems. In this work, polyetherimide (PEI) matrix composite films with field-dependent nonlinear conductive behavior were fabricated by using a typical type of transition metal dichalcogenides, MoS2 as filler. The MoS2 filled PEI composite film showed a nonlinear coefficient of 6.92 at a relatively low filler content of 15 phr, which is the percolation threshold of this kind of composite film. Nonlinear conductive behavior of the MoS2/PEI composites was driven by tunneling effect. Conductivity of the 20 phr of MoS2 filled composite film increased for almost 3 magnitudes within 20 kV/mm. Enhanced dielectric constant was brought to PEI by the MoS2 fillers. The PEI containing 20 phr of MoS2 showed a dielectric constant of 6.1 at 1 kHz with dielectric loss still being low. This work revealed the potential of MoS2 being adopted as filler of field grading composites. [ABSTRACT FROM AUTHOR]

The kinetics of fast thermal curing epoxy resin and the fast-curing ability initiated by 4- hydroxyphenyl dialkyl sulfonium salt cationic curing agent were discussed. The curing reaction is driven by two chain propagation mechanisms. At the initial stage of the polymerization, the propagation is dominated by activated chain end (ACE) mechanism with a faster curing rate. At long time of the polymerization, the propagation is dominated by activated monomer (AM) mechanism with a lower curing rate. With the increase of curing agent content, the activation energy of ACE mechanism reduces, however, the activation energy of AM mechanism decreases first and then increases. In addition, the surface curing test was used to evaluate the fast-curing ability of this epoxy system. By adopting preferred formulation and process, this epoxy system could be cured in several seconds. [ABSTRACT FROM AUTHOR]

Accurate remaining useful life (RUL) prediction of lithium-ion battery is very important for the safety of power system of mobile equipment. At present, most of the currently proposed RUL prediction methods for lithium-ion batteries are limited by the length of the training data, and the RUL is also difficult to predict when the predicted dataset is different from the training dataset in terms of the mapping of operating conditions, and the results obtained are difficult to achieve the desired accuracy. To solve this problem, in this work, a new model is proposed. It is a fusion of the long short-term memory (LSTM) network model based on transfer learning and particle filter (PF) model. LSTM based on transfer learning (TL-LSTM) is used for long-term prediction of the lithium-ion battery capacity, which makes the model have the generalization ability to deal with the RUL prediction under different stress. Since LSTM predicts RUL as a single-point prediction, we introduce a PF model to increase the uncertainty representation of RUL prediction. The predicted value from TL-LSTM model is used as observation for the PF prediction model, and the predicted value is continuously adjusted and updated during the iterative process to achieve the uncertainty representation and improve accuracy. The model is validated with the actual tested battery cycle dataset. The experimental results show that the method is effective for the RUL prediction problem of the mapping under different working conditions, and the relative error is less than 5% when the data length is 50%, which proves the application potential of the method. [ABSTRACT FROM AUTHOR]

In this work, core-shell structured polydopamine coated silver nanowires (Ag@PDA NWs) and polydopamine coated BaTiO 3 nanoparticles (BT@PDA NPs) are accurately prepared. Through embedding Ag@PDA NWs and BT@PDA NPs into the P(VDF-HFP) matrix, flexible nanocomposites with high dielectric constant and low dielectric loss are prepared by constructing three-phase structure. The crystal structure, thermal properties and dielectric properties of the nanocomposites are fully investigated. Compared with two-phase nanocomposites, which are composed by Ag@PDA NWs and P(VDF-HFP), the dielectric constant of the three-phase nanocomposites is improved from 28.1 to 67.9. Additionally, owing to the presence of the polydopamine shell, the nanofillers are homogeneously dispersed and the interfacial adhesion between the nanofillers and polymer matrix is also enhanced, leading to the dielectric loss and electric conductivity of three-phase nanocomposites remain relatively low level. Furthermore, the dielectric properties of the three-phase nanocomposites exhibit weak temperature dependence. [ABSTRACT FROM AUTHOR]

Background: Human papillomavirus (HPV) infection is currently the main cause of cervical cancer and precancerous lesions in female patients. By analyzing 6-year patient data from Shanghai Zhoupu Hospital in China, we retrospectively analyzed the epidemiological characteristics of women to determine the relationship between HPV genotype and cytological test results. Methods: From 2014 to 2019, 23,724 cases of cervical shedding were collected from Zhoupu Hospital in Shanghai, China. By comparing the results of HPV and ThinPrep cytology test (TCT), the HPV infection rate of patients was retrospectively analyzed. HPV genotyping using commercial kits can detect 21 HPV subtypes (15 high-risk and 6 low-risk). According to the definition of the Bethesda system, seven types of cervical cytology results were involved. Results: 3816 among 23,724 women, nearly 16.08%, were infected with HPV. The top three highest HPV prevalence rates were high-risk type infection, including HPV52 (3.19%), 58 (2.47%) and 16 (2.34%). The number of single-type HPV infections (3480 (91.20%)) was much larger than the number of multi-type ones (336 (8.8%)). Single-type infections were mainly in women aged 50–60 (16.63%) and women under 30 (15.37%), while multi-type infections were more common in women over 60 (2.67%). By analyzing the long-term trends, between 2014 and 2019, HPV52, 58, and 16 subtypes changed significantly, and the HPV positive rate also changed significantly during this period. Among 4502 TCT positive women, 15 (4.04%), 125 (2.64%),159 (1.54%), 4202 (17.71%) and 1 (0.004%) had atypical glandular cells (AGC), high-grade squamous intraepithelial lesions (HSIL), low-grade squamous intraepithelial lesions (LSIL), atypical squamous cells (ASC)and cervical adenocarcinoma, respectively. The HPV infection rates were 66.08%, 63.99%, 115.20%, 119.50%, and 31.72% for NILM, AGCs, HSILs LSILs and ASCs, respectively. Conclusions: HPV and TCT screening were very important steps in the secondary prevention of cervical cancer. Through the tracking and analysis of HPV and TCT results in this study, it can provide valuable information for Shanghai's HPV screening and prevention strategies, and provide references for clinical decision-making in the treatment of cervical cancer and precancerous lesions. [ABSTRACT FROM AUTHOR]

In this study, gold–palladium nanoparticles (Au–PdNPs) stabilized by poly(amic acid) salt (PAAS) were prepared by a one-pot method and then characterized by transmission electron microscope (TEM), X-ray diffractometer (XRD), ultraviolet–visible spectrophotometer (UV–Vis) and X-ray photoelectron spectroscope (XPS). The Au–PdNPs which possess bimetallic structures were assessed as an efficient quasi-homogenous catalyst for the oxidation of amines in aqueous phase to prepare imines. Outstanding activity was displayed and a maximum conversion of almost 100% was reached for the oxidative condensation of benzylamine. Synergistic effect between Au and Pd atoms was proved by the catalytic results. The catalyst demonstrated a remarkable stability as it could be recycled for 5 times by taking advantage of pH-sensitivity of PAAS. [ABSTRACT FROM AUTHOR]

In this work, we have developed a rapid and simple approach for fabrication of graphene-like materials. It consisted of shearing commercial graphite in aqueous solution with the assistance of ultrasonication. The results showed that the graphene-like materials were successfully fabricated with not only similar flake structure of graphene, but also improved conductivity. For the applications of flexible supercapacitors, the as-prepared graphene-like materials showed better specific capacitance than commercial graphite as the working electrode. In addition, the rate capability of the flexible supercapacitor device is 80% and the capacitance retention reaches 90% after 10,000 cycles. The high flexibility of the as-fabricated graphene-like materials gives rise to high flexibility of all-solid-state supercapacitors, and the specific capacitance was not affected by bending state. The as-fabricated supercapacitor further demonstrated that it can drive the resistive pressure sensor and the voltage was stable at a fixed value under different values of pressure. [ABSTRACT FROM AUTHOR]

Water‐soluble Au−Ag bimetallic nanoparticles with different Au/Ag molar ratios stabilized by poly (amic acid) salt (PAAS) were synthesized by a one‐pot method and characterized by ultraviolet‐visible spectrophotometer (UV‐vis), X‐ray diffractometer (XRD), X‐ray photoelectron spectroscope (XPS) and High‐Angle Annular Dark Field scanning transmission electron microscope (HAADF‐STEM). The Au−Ag/PAAS catalysts displayed high activity for the aerobic oxidative coupling reaction of alcohols and amines in water. Attributing to the synergistic effect between Au and Ag, the activity of the bimetallic catalysts was superior to that of the corresponding monometallic catalysts. The catalyst with an Au/Ag molar ratio of 6/1 showed the best catalytic performance, which could be easily recovered and reused without significant loss of activity for over 5 times due to the pH response of PAAS. [ABSTRACT FROM AUTHOR]

Highly dispersed poly(amic acid) salt-stabilised palladium nanoparticles(PdNPs/PAAS) were synthesised via a facile reduction strategy in aqueous media at room temperature and characterised by transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and inductively coupled plasma optical emission spectrometer. The nanoparticles were used as catalyst for Suzuki-Miyaura coupling reaction to synthesise biphenyl compounds in short reaction time and high yields under mild conditions, benefiting from highly efficient quasi-homogeneous catalytic activity. The catalyst could be recycled 5 times without obvious loss attributing to the pH response of the PAAS. [ABSTRACT FROM AUTHOR]

Oligomeric amyloid-beta (Aβ) peptides are considered as the most toxic species in Alzheimer's disease (AD). Monitoring of the Aβ aggregation profiles is critical for elucidating the oligomer toxicity and may serve as a therapeutic target for AD. By immobilizing the capture antibodies of A11 and OC that are specific to the oligomers and fibrils, respectively, in separate fluidic channels, a novel surface plasmon resonance (SPR) biosensor was designed for monitoring the oligomeric and fibrillar species of Aβ(1–42) simultaneously. The influence of curcumin, Cu2+ and methylene blue on the amount of toxic oligomers and fibrils was evaluated. The half maximal inhibitory concentration (IC50) of curcumin and methylene blue was determined. The formation of Aβ fibrils was also validated by the thioflavin T (ThT) fluorescence assay. The results demonstrate the utility of SPR as an analytical tool for rapid and comprehensive monitoring of Aβ aggregation and screening of Aβ modulators. [ABSTRACT FROM AUTHOR]

Monitoring and predicting traffic conditions are of utmost importance in reacting to emergency events in time and for computing the real-time shortest travel-time path. Mobile sensors, such as GPS devices and smartphones, are useful for monitoring urban traffic due to their large coverage area and ease of deployment. Many researchers have employed such sensed data to model and predict traffic conditions. To do so, we first have to address the problem of associating GPS trajectories with the road network in a robust manner. Existing methods rely on point-by-point matching to map individual GPS points to a road segment. However, GPS data is imprecise due to noise in GPS signals. GPS coordinates can have errors of several meters and, therefore, direct mapping of individual points is error prone. Acknowledging that every GPS point is potentially noisy, we propose a radically different approach to overcome inaccuracy in GPS data. Instead of focusing on a point-by-point approach, our proposed method considers the set of relevant GPS points in a trajectory that can be mapped together to a road segment. This clustering approach gives us a macroscopic view of the GPS trajectories even under very noisy conditions. Our method clusters points based on the direction of movement as a spatial-linear cluster, ranks the possible route segments in the graph for each group, and searches for the best combination of segments as the overall path for the given set of GPS points. Through extensive experiments on both synthetic and real datasets, we demonstrate that, even with highly noisy GPS measurements, our proposed algorithm outperforms state-of-the-art methods in terms of both accuracy and computational cost. [ABSTRACT FROM AUTHOR]

A simple and efficient method for in situ preparation of highly stable polyimide (PI)-supported silver nanoparticles (AgNPs) was proposed. This process achieves excellent dispersion and high stability of AgNPs in the PI matrix. The formation of AgNPs in PI and the morphology evolution of PI/Ag nanocomposites were characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and x-ray photoelectron spectra studies. The catalytic properties of these PI-supported AgNPs were investigated by monitoring the reduction of 4-nitrophenol by excess NaBH4 in water. The catalytic reaction was observed to have a pseudo first-order rate constant of 0.567 min−1 (9.45 × 10−3 s−1), which is comparable to other heterogeneous silver catalysts reported in the literature. Notably, the PI-supported AgNPs retained their relatively high catalytic activity over seven recycles with almost no leaching of catalytic species in the reaction solution. Moreover, the catalytic activity of the catalyst is still quite appreciable even after a six-month shelf-storage under room temperature. [ABSTRACT FROM AUTHOR]

High dielectric permittivity materials are much desirable in the electric industry. Filling polymer matrix with conductive powders to form percolative composites is one of the most promising methods to achieve high dielectric permittivity. However, they do not always provide high mechanical properties and thermal stability, which seriously limit their applications. In this study, we present the preparation of functional core-shell structured silver nanowires/polyimide (AgNWs/PI) hybrid film with high dielectric permittivity and low loss dielectric. The core-shell structure of AgNWs was characterized by transmission electric microscopy. The dynamical mechanical analysis showed that AgNWs/PI hybrid films had relative high dynamic mechanical properties with storage modules over 1 Gpa. Moreover, the hybrid films exhibited excellent thermal stability with 5 % weight-loss temperature above 500 °C. The dielectric properties of the carbon-coated AgNWs hybrid films were remarkably improved. The maximum dielectric permittivity of hybrid films is 126 at 10Hz, which was 39 times higher than that of pure PI matrix, while the dielectric loss of that is still remained at a low value. This study showed a new method to improve the dielectric, dynamic mechanical and thermal properties of films. [ABSTRACT FROM AUTHOR]

A new series of core-shell structured silver/polyimide (PI) nanocomposites was prepared by in situ polymerization followed by the chemical imidization of poly(amic acid) (PAA, precursor of PI) at a low temperature. The TEM images showed that the silver cores of the nanocomposites were encapsulated with homogeneous shells with thickness of 4 and 8 nm at silver contents of 90 and 60 %, respectively. The shell thickness was controlled by varying the content of PAA. FTIR spectroscopic analysis indicated that the imide ring formation occurred after the chemical imidization. The Ag/PI nanocomposites showed excellent thermal stability and exhibited only 10 % weight loss at 300 °C in the air. Moreover, percolation was observed at silver weight fractions close to the critical value, and the maximum dielectric permittivity of the nanocomposites was 120, which is about 40 times higher than that of pristine PI. [ABSTRACT FROM AUTHOR]

A series of polyimide composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization. To increase the chemical compatibility of carbon nanotubes with the polyimide matrix, MWNTs were treated with an acid mixture and sulfoxide chloride in turn. The modified MWNTs are dispersed homogeneously in the matrix while the structure of the PI and MWNTs are stable in the preparation process. The composite films hold preferable thermal stability the same as the pure PI. The composite films exhibited good thermomechanical properties. The storage modulus increased significantly by increasing MWNT content and decreasing the enhancement of temperature. The films’ glass transition temperature increased with enhancing of MWNTs frictions. The dielectric constants of the composites decrease with increasing frequency and increase sharply with the adding of MWNTs, which is favorable for practical use in anti-static materials and embedded capacitors. [ABSTRACT FROM PUBLISHER]

Several poly(vinylidene fluoride- ter-chlorotrifluoroethylene- ter-trifluoroethylene) terpolymers, including 68 mol % vinylidene fluoride, were prepared by the partial reduction of chlorine in poly(vinylidene fluoride- co-chlorotrifluoroethylene) copolymers. The terpolymers were then allowed to crystallize under two sets of conditions: (1) crystallized from solution (in N,N-dimethylformamide) at 35°C for 108 h and (2) annealed at temperatures 5°C below their respective melting points for 11 h. The effect of the chlorotrifluoroethylene (CTFE) content and crystallization conditions on the crystallization behavior of the terpolymers was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The results show that with increasing CTFE content, the terpolymers contained less of the β phase (it even disappeared), which had an all-trans chain conformation, and more of the γ phase was found, which became prominent with the trans-trans-trans-gauche conformation. The crystallinity, crystal size, fusion enthalpy, and melting temperatures of the terpolymers decreased with increasing CTFE content. Compared with annealed terpolymers, the terpolymers crystallized from the solution at 35°C included more polar components that contained more trans conformations but had lower crystallinities, melting temperatures, and fusion enthalpies and smaller crystal sizes. These results suggest that crystallization from the solution may be helpful in forming polar crystals, whereas an annealing process at a high temperature is beneficial in perfecting the crystal structure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

number of solution-casted poly(vinylidenefluoride-chlorotrifluoroethylene-trifluoroethylene) [P(VDF-CTFE-TrFE)] terpolymer films with different CTFE content have been characterized by a series of thermal analysis techniques, including thermogravimetric analysis (TG), differential scanning calorimetry, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA). The work intends to provide more comprehensive information about thermal behavior of these ferroelectric polymers. TG results suggest that the introduction of the CTFE units slightly decreases the thermal stability of the polymer due to the instability of C-Cl bond during heating. DMA detected a relatively weak α relaxation and a broad α relaxation in the samples of low CTFE content. These two relaxation processes completely mixed together in the sample with high CTFE content, revealing the crystalline structures in the polymer, become a more imperfect and diffuse state as CTFE units increasing. The polymer with less CTFE units possesses an enhanced stiffness due to its higher degree of crystallinity. A contraction process after a slight amount of thermal expansion upon heating is detected by TMA, due to the release of internal tensile strain/stress generated during solidification of the films. The higher crystallinity of the polymer film generated the greater strain/stress, leading to the larger degree of shrinkage. Also, the higher melting point of the polymer with less CTFE units allows the film soften at a higher temperature. [ABSTRACT FROM AUTHOR]

Three series of tolane‐based liquid crystalline compounds with a fluorinated polar end group have been synthesized. Their phase transition temperatures were measured by texture observation in a polarizing microscope and confirmed by DSC. The all‐fluorinated trifluoromethyl and trifluoromethoxy group have a tendency to promote the smectic A phase, but the difluoromethoxy group has the tendency to promote a wide nematic phase. [ABSTRACT FROM AUTHOR]

Three series of fluorinated phenyl 4-[(4- n -alkoxy-2,3-difluorophenyl)ethynyl]benzoate liquid crystals have been synthesized. Their phase transition temperatures were measured by texture observation in a polarizing microscope and confirmed by DSC. Their mesomorphic properties and fluoro-substituent effects were studied in detail. [ABSTRACT FROM AUTHOR]

Making use of defects modification to P(VDF-TrF'E) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor k31 of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, &Sim;1 J/cm³. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chlorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a non-polar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the non- polar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/cm³ can be induced under a low applied field of 13 V/μm. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa. [ABSTRACT FROM AUTHOR]

Two series of 4-(3-alkoxycarbonylpyridyl-6-ethynyl)phenyl trans-4-n-alkylcyclohexylcarboxylates and 4-(3-alkoxycarbonylpyridyl-6-ethynyl)phenyl 4-(trans-4-n-alkylcyclohexyl)benzoates have been prepared. Their mesmorphic properties were observed and measured by polarizing optical microscopy and differential scanning calorimetry. The relationship between structures and properties is discussed, showing that the ferroelectric phase can be observed when chiral terminal chains exist. [ABSTRACT FROM AUTHOR]

Two resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl]benzoate liquid crystals were prepared and their mesomorphic properties observed and measured. Achiral antiferroelectric phases were seen with increasing length of the hydrocarbon terminal chains. [ABSTRACT FROM AUTHOR]

Twenty new 2,5-disubstituted 1,3-dioxans were prepared, and their mesomorphic properties were investigated by optical polarizing microscopy and DSC; all of the compounds exhibit the nematic phase only. With fluorination in the mesogenic core, the melting and clearing points were reduced, but their nematic phase range only slightly shortened. [ABSTRACT FROM AUTHOR]

Four series of azobenzene liquid crystal compounds containing a fluorinated tolan unit have been synthesized. The mesomorphic behaviours of these compounds were characterized by differential scanning calorimetry and optical polarizing microscopy. The compounds of these series exhibit a nematic, a smectic C or a smectic B phase. This investigation revealed that the alkoxy chain at the side of the azobenzene moiety plays a more important role in the formation of smectic phases than the one at the side of the tolan moiety. [ABSTRACT FROM AUTHOR]

Three series of novel fluorinated liquid crystals containing a 2,3-difluorotolan unit have been synthesized. Their phase transition temperatures have been measured by texture observation in a polarizing microscope and confirmed by DSC. The influence of the lateral fluoro-substitution is discussed. [ABSTRACT FROM AUTHOR]

Three homologous series of new compounds containing 2,3-difluorophenylene and trans-1,4-substituted cyclohexane have been synthesized by a coupling reaction with Pd(PPh[sub 3])[sub 2]Cl[sub 2] as the catalyst. Their liquid crystalline properties have been studied by optical polarizing microscopy and DSC. The relationship between the properties and chemical structures of the target compounds is discussed in detail. [ABSTRACT FROM AUTHOR]

Two series of chiral and achiral 4-[(3-n-alkoxycarbonylpyridyl)-6-ethynyl]phenyl 4-(trans-4-n-alkylcyclohexyl)benzoate liquid crystals have been synthesized. Their mesomorphic properties were observed and measured by polarizing optical microscopy and DSC. A broad chiral smectic C phase was observed when terminal chains contained a chiral centre. [ABSTRACT FROM AUTHOR]

Development of highly active and recyclable catalysts for selective hydrogenation of nitroarenes to amines in water at room temperature is always a challenge in chemical industry. This study reports a facile in situ method for synthesis of ultrafine palladium and platinum nanoparticles (NPs) stabilized by poly (amic acid) salt (PAAS) and their potential as catalysts for hydrogenation of nitroarenes with sodium borohydride or molecular hydrogen as reductant in water at room temperature. In the reduction of 4‐nitrophenol to 4‐aminophenol by sodium borohydride, the activity parameters of PdNPs–PAAS and PtNPs–PAAS catalyst is 6.66 × 103 and 5.58 × 103 s−1 M−1 respectively. In the hydrogenation of diverse nitroarenes under atmospheric hydrogen pressure, PdNPs–PAAS shows high activity but poor selectivity toward desired amines in some cases, while PtNPs–PAAS shows both high activity and high selectivity for selective hydrogenation of nitroarenes to corresponding anilines. The high efficiency of nanocatalyst is due to the quasi‐homogeneous dispersion of metal NPs and synergistic effects between metal NPs and PAAS. In addition, nanocatalyst can be easily recovered with pH‐sensibility of PAAS and reused at least six times without significant loss of catalytic activities. Poly (amic acid) salt (PAAS)‐mediated Pd and Pt NPs have been studied in the catalytic hydrogenation of nitro‐compounds in water at ambient conditions, with high activities and high‐performance, pH‐responsive recyclability and reusability. In particular, the PtNPs–PAAS catalyst combines a good activity and a high selectivity for target amines, without hydrogenation intermediates and by‐products detected in the final products. The high efficiency is mainly due to the quasi‐homogeneous dispersion of metal NPs and the synergistic effects between metal NPs and PAAS. [ABSTRACT FROM AUTHOR]