High-entropy alloys have received considerable attention in the field of catalysis due to their exceptional properties. However, few studies hitherto focus on the origin of their outstanding ...performance and the accurate identification of active centers. Herein, we report a conceptual and experimental approach to overcome the limitations of single-element catalysts by designing a FeCoNiXRu (X: Cu, Cr, and Mn) High-entropy alloys system with various active sites that have different adsorption capacities for multiple intermediates. The electronegativity differences between mixed elements in HEA induce significant charge redistribution and create highly active Co and Ru sites with optimized energy barriers for simultaneously stabilizing OH
and H
intermediates, which greatly enhances the efficiency of water dissociation in alkaline conditions. This work provides an in-depth understanding of the interactions between specific active sites and intermediates, which opens up a fascinating direction for breaking scaling relation issues for multistep reactions.
The thermo-oxidative degradation of polyamide 6 (PA6) was studied at relative high temperatures (between 120 and 170 °C) using oxygen uptake and hydroperoxide determination methods, ...chemiluminescence, FT-IR and UV–VIS spectroscopy as well as solution viscosity and tensile property measurements.
The relation between the results of the different analytical techniques and influence of temperature on these relations was determined. Arrhenius plots of the degradation determined with the different methods are linear; however the activation energies determined from these plots depend on the analytical method used. For oxygen uptake measurements and changes in UV absorbance (at 280 nm) and solution viscosity an activation energy of about 120 kJ/mol was calculated, for the increase in carbonyl index of about 80 kJ/mol and for the decrease in elongation at break of about 150 kJ/mol.
The changes in oxygen uptake UV absorbance and solution viscosity are probably due to the same chemical process. The lower activation energy from changes in the carbonyl index is attributed to the formation of gaseous products, which play a larger role at higher temperatures. The higher activation energy from the elongation at break measurements was ascribed to the contribution of physical changes that play the largest role at the highest temperatures.
Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. However, the fabrication of self‐standing hydrogels ...merely composed of conducting polymers is still challenging owing to the absence of reliable methods. Herein, a novel and facile macromolecular interaction assisted route is reported to fabricate self‐standing hydrogels consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4‐ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity). Owing to the synergistic effect between them, the self‐standing hydrogels possess good mechanical properties and electronic/electrochemical performances, making them an excellent potential electrode for solid‐state energy storage devices. A proof‐of‐concept all‐hydrogel‐state supercapacitor is fabricated, which exhibits a high areal capacitance of 808.2 mF cm−2, and a high energy density of 0.63 mWh cm−3 at high power density of 28.42 mW cm−3, superior to many recently reported conducting polymer hydrogels based supercapacitors. This study demonstrates a novel promising strategy to fabricate self‐standing conducting polymer hydrogels.
Standing on its own: Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. A novel and facile two‐step route is proposed to fabricate a self‐standing hydrogel consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4‐ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity) for an all‐hydrogel‐state supercapacitor.
The oxidative degradation behavior of polymers depends on a combination of chemical and physical factors, with oxygen diffusion being one of the most important, especially when the oxygen consumption ...rate is larger than its permeability.
As a result of diffusion limited oxidation (DLO), at high temperatures the degradation rate of polyamide 6 (PA6) plaques is heterogeneous, with the polymer oxidizing much faster at the surface than in the bulk. Normalized carbonyl index (CI) and UV absorption – depth profiles were found to be mostly degradation time independent, implying equilibrium degradation conditions where oxygen permeability and reaction rates did not change significantly with degradation time. The experimental DLO profiles were described using a basic reactive-diffusion model based on Fickian oxygen diffusion and an oxidation rate being first order in local O2 concentration, as well as by applying an established DLO model based on the basic autoxidation mechanism. Analysis with the second model yielded the best estimation of high temperature oxygen permeability (PO2) data. It also showed some of the limitations in the data analysis when using a simple first order DLO model.
It was shown that stabilizers have an influence on the oxidation - depth profiles. Better stabilization results in slower polymer oxidation and the oxidation – depth profiles are therefore less pronounced. At 170 °C it was observed that stabilized plaques (0.5 mm) in the center oxidize faster than unstabilized plaques, which is attributed to the complete consumption of oxygen in the outer layers for the unstabilized plaques. Oxidation rates of differently stabilized samples were also determined by applying the second DLO model.
This work investigated, for the first time, the role of nanosized lignin (LNP), in comparison with microlignin (LMP), when introduced at two different weight amounts (5% and 10 wt%) in bulk ...phenol–formaldehyde resol as adhesive. Morphological analysis was performed to check out the dispersion and interfacial bonding of lignin in the phenolic resin. The curing process has been examined by differential scanning calorimetry (DSC), while the thermal stability of the composites has been evaluated by using thermogravimetric (TGA) and thermo-mechanical (TMA) analysis. Results exhibited that small amount of lignin could both favor the thermal cure reaction, due to its abundance of phenylpropane units, and the initial thermal resistance could be consequently improved, especially when the nano-sized lignin was used. Meanwhile, the effect of micro- and nano-modification on tensile shear strength of wood lap joints based on lignin-phenol–formaldehyde resol adhesives was also analyzed. Results showed that 5 wt% of LNP could positively increase the shear strength from 8.7 to 10.9 MPa, opening the possibility of using environmental friendly nanoscale lignin in cross linked traditional phenol wood adhesives with enhanced adhesion performance, strongly related to nanoparticles higher specific surface area and reactivity.
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•Nanosized (LNP) and microlignin (LMP) were added to phenol–formaldehyde resol adhesive.•Nanolignin could both favor the cure reaction, due to its abundance of phenylpropane units.•Nanosized lignin homogenously dispersed absorbed and inhibited dimensional changes.•Higher specific surface area and reactivity for LNP increase the shear strength of wood joints.
•Design principles of silicon-based aerogel thermal insulation materials are introduced.•Performance optimization strategies of SA-TIMs are elaborated in detail.•Relationship between the composition ...and final properties of SA-TIMs is reported.•Five different microstructures composed of second phase materials and SA are reported.•Future research direction of SA-TIMs are analyzed according to their practical applications.
Silicon-based aerogel (SA) has attracted increasingly more attention in the field of thermal insulation as its extraordinary properties such as ultralight, ultra-low thermal conductivity, and strong designability. However, SA thermal insulation materials (SA-TIMs) have several intrinsic defects such as low strength and poor toughness, which make their processing and handling difficult and restrict their practical applications. Composition optimization and microstructure reconstruction are the most convincing and effective strategies to improve their mechanical and thermal insulation properties, achieve more functions, and reduce cost. This review encompasses a complete survey of scientific achievements related to the two strategies, describing their characteristics, microstructures, and properties. The influence of different compositions and various assembly structures on the final properties of SA-TIMs is thoroughly reported. The main focus of this review is to point out the design principles of SA-TIMs and discuss the most promising development trends towards their widespread applications.
Biodegradable poly(lactide)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends were prepared by reactive blending in the presence of chain-extenders. Two chain-extenders with multi-epoxy ...groups were studied. The effect of chain-extenders on the morphology, mechanical properties, thermal behavior, and hydrolytic degradation of the blends was investigated. The compatibility between the PLA and PBAT was significantly improved by in situ formation of PLA-co-PBAT copolymers in the presence of the chain-extenders, results in an enhanced ductility of the blends, e.g., the elongation at break was increased to 500% without any decrease in the tensile strength. The differential scanning calorimeter (DSC) results reveal that cold crystallization of PLA was enhanced due to heterogeneous nucleation effect of the in situ compatibilized PBAT domains. As known before, PLA is sensitive to hydrolysis and in the presence of PBAT and the chain-extenders, the hydrolytic degradation of the blend was evident. A three-stage hydrolysis mechanism for the system is proposed based on a study of weight loss and molecular weight reduction of the samples and the pH variation of the degradation medium.
Silver nanoparticles (AgNPs) with a diameter of 3–6 nm were uniformly reacted onto the surface of nanocrystal cellulose (NCC) via complexation leading to NCC–Ag nanohybrids with an AgNP content of 8 ...wt %. Subsequently, antibacterial green nanocomposites containing renewable and biodegradable poly(lactide) (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and NCC–Ag nanohybrids were synthesized and investigated. The PBAT as flexibilizer improved the toughness of the PLA matrix while the uniformly dispersed NCC–Ag nanohybrids enhanced the compatibility, thermal stability, crystallization, and antibacterial properties of the PLA/PBAT blends. The crystallization rate and the storage modulus (E′) of the green nanocomposites were increased obviously with increasing content of CNC–Ag nanohybrids. Meanwhile, notably the antibacterial activity of the PLA/PBAT/NCC–Ag nanocomposites was achieved against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus cells. The antibacterial performance was mainly related to the antibacterial nature of the finely dispersed NCC–Ag nanohybrids. The study demonstrates great potential of the green nanocomposites in functional packaging and antibacterial textile applications.
Manufacturing hybrid electrodes with the combination of electroactive materials and carbon carriers brings hope for high-performance supercapacitors, but the poor interfacial compatibility between ...hydrophobic carbon substrate surface and active materials is still the bottleneck to be solved. Here, we propose a superhydrophilic strategy to stabilize NiCo
2
S
4
on inert carbon cloth (CC) using nitrogen-doped (N-doped) carbon layer as structure/interface coupling bridge, so as to prepare hybrid material (expressed as NiCo
2
S
4
/CC-CN) for supercapacitor. The N-doped carbon layer on CC leads to the formation of superhydrophilic surface/interface, which is conducive to the uniform growth of NiCo
2
S
4
on CC and helps to effectively strong coupling interaction between CC and NiCo
2
S
4
. In addition, the asymmetric supercapacitor made of NiCo
2
S
4
/CC-CN as the positive electrode and as-prepared activated carbon cloth (PACC) as the negative electrode provides a high energy density of 0.11 mWh cm
−2
at a power density of 0.35 mW cm
−2
. The interfacial engineering in this study holds the potential of creating high energy density electrodes for advanced energy storage.
Melanin is a kind of ubiquitous natural pigment, which serves a variety of protective functions in many organisms. In the present study, natural melanin and synthetic melanin nanoparticles (NPs) were ...systematically investigated for its potential application in polymeric optical materials. A significant short-wavelength shielding and high visible light transparency polymer nanocomposite was easily obtained via tuning the melanin particle size. In particular, the nanocomposite film with melanin NPs (diameter ≈ 15 nm) loading even as low as 1 wt % blocks most ultraviolet light below 340 nm and still keeps high visible light transparency (83%) in the visible spectrum. More importantly, because of the excellent photoprotection and radical scavenging capabilities of melanin, the resulting polymer nanocomposite exhibits outstanding photostability. In effect, such fantastic melanin NPs is promising for applications in various optical materials.
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