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Global climate change has posed widespread challenges to the ecological process critical to the fitness of many wild organisms, such as reproductive phenology. Many bird species have advanced their reproductive phenology in response to the increases in spring temperatures. However, the mechanism of how climate influences the timing of breeding is still often unclear in many species. We explored the relationship between the timing of breeding and spring temperatures based on 14 years of data on hair‐crested drongos Dicrurus hottentottus in the wild. By applying a 'sliding window' approach, we aimed to identify the time window and weather variable that best explains the timing of breeding at both population and individual levels. We found that the more nights with a minimum temperature below 17°C, around three weeks earlier than the peak reproduction, delayed the breeding time. Low night temperatures may force females to allocate more energy to thermoregulation and therefore physiologically constrain egg‐laying. Although annual minimum and maximum temperatures have increased over the study period, the timing of breeding showed no trend as there was no change in the number of low‐temperature nights in the relevant period across years. The repeatability of the laying date for individual females (R = 0.211) and across the years (R = 0.270) were low indicating that drongos were flexible in adjusting their breeding phenology to environmental variation. These results suggest an effect of low night temperature on avian breeding phenology. This effect may apply commonly across bird species considering shared physiological constraints. [ABSTRACT FROM AUTHOR]

Solar desalination is a promising strategy to utilize solar energy to purify saline water. However, the accumulation of salt on the solar evaporator surface severely reduces light absorption and evaporation performance. Herein, a simple and eco‐friendly method to fabricate a 3D gradient graphene spiral sponge (GGS sponge) is presented that enables high‐rate solar evaporation and zero liquid discharge (ZLD) desalination of high‐salinity brine. The spiral structure of the GGS sponge enhances energy recovery, while the gradient network structures facilitate radial brine transport and directional salt crystallization, which cooperate to endow the sponge with superior solar evaporation (6.5 kg m−2 h−1 for 20 wt.% brine), efficient salt collection (1.5 kg m−2 h−1 for 20 wt.% brine), ZLD desalination, and long‐term durability (continuous 144 h in 20 wt.% brine). Moreover, the GGS sponge shows an ultrahigh freshwater production rate of 3.1 kg m−2 h−1 during the outdoor desalination tests. A continuous desalination–irrigation system based on the GGS sponge for crop growth, which has the potential for self‐sustainable agriculture in remote areas is demonstrated. This work introduces a novel evaporator design and also provides insight into the structural principles for designing next‐generation solar desalination devices that are salt‐tolerant and highly efficient. [ABSTRACT FROM AUTHOR]

Torsional compliance of the torque transducer can be an important issue in linear viscoelastic (LVE) measurements when the sample stiffness is high relative to the instrument stiffness. We evaluated compliance effects of the ARES 2K-FRT on LVE measurements by systematically comparing the results of the frequency sweep mode obtained with 25 and 8 mm plates, respectively. In addition to the transducer, the test fixtures do contribute significantly to the system compliance. Without correction, the upper limit for the complex modulus ∣ G ∣ is approximately close to 4 × 10 Pa at 10% uncertainty, when using 25 mm plates. This limit is lower than the plateau modulus $\left( {G_N^0 } \right)$ of most polymers. Therefore, instrument compliance can lead to significant errors for $G_N^0 $ and wrong scaling for G in the plateau and Rouse regions. The respective roles of transducer and tool compliances are discussed. The FRT transducer compliance is corrected in real time in the instrument firmware. Tool compliance is a common problem for all rheometers when measuring stiff samples. [ABSTRACT FROM AUTHOR]

Abstract: Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell''s equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits. [Copyright &y& Elsevier]

Abstract: Photonic crystals have many potential applications because of their ability to control light-wave propagation. We report on the fabrication and properties of quasi-two-dimensional photonic crystals with triangular lattices of dielectric rods in air. Rod-type photonic crystal structures were fabricated in silicon by electron beam lithography and dry-etching techniques. Mach–Zehnder interferometers were fabricated from two-dimensional photonic crystal waveguides. Transmission spectra were measured and device operation was shown to be in agreement with theoretical calculations. The interferometers can be used in the visible light region. Such an approach to photonic element systems should enable new applications for designing components in photonic integrated circuits. [Copyright &y& Elsevier]

Abstract: The adiabatic shearing behavior of S15C low carbon steel, S50C medium carbon steel, and SKS 93 tool steel with a high carbon and low alloy content (abbreviated to high carbon steel hereafter) is examined using a compressive-type split-Hopkinson pressure bar (SHPB) at strain rates ranging from (5–20)×104 s−1. Metallographic observations of the sheared specimens suggest that the shear flow stress and the hardness and width of the shear band depend strongly on the carbon content and strain rate. The formation of the deformed and martensitic transformed shear bands is a function of the carbon content and the shear load. The fracture surface of the low carbon steel exhibits a dimple-like structure. However, the fracture surfaces of the medium and high carbon steels exhibit both a dimple-like structure and knobby features. The formation of the knobby features is attributed to an increased carbon content and a higher strain rate. [Copyright &y& Elsevier]

Abstract: Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable bandgap in a three-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic dielectric sphere in the liquid crystal medium is studied by solving Maxwell''s equations using the plane wave expansion method. The photonic band structures are found to exhibit partial bandgaps for the simple-cubic lattices. Numerical simulations show that the bandgaps can be continuously tuned in simple-cubic lattices consisting of anisotropic dielectric spheres by infiltrating nematic liquid crystals. We analyzed the variations of bandgap by considering various modulation of electric field. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits. [Copyright &y& Elsevier]

Abstract: Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable full bandgap in a three-dimensional PC structure modulated by a nematic liquid crystal (LC). Numerical simulations show that the band gaps can be continuously tuned in a diamond dielectric structure consisting of air spheres by infiltrating nematic LCs. Then we can control the full bandgap of a PC structure. We analyzed the variations of full gap by considering various index modulations of LCs. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits. [Copyright &y& Elsevier]

Abstract: A compressive type split-Hopkinson pressure bar is utilized to compare the impact plastic behaviour of three steels with different levels of carbon content. S15C low carbon steel, S50C medium alloy heat treatable steel (abbreviated hereafter to medium carbon steel) and SKS93 tool steel with a high carbon and low alloy content (abbreviated hereafter to high carbon steel) are tested under strain rates ranging from 1.1×103 s−1 to 5.5×103 s−1 and temperatures ranging from 25 to 800°C. The effects of the carbon content, strain rate and temperature on the mechanical responses of the three steels are evaluated. The microstructures of the impacted specimens are studied using a transmission electron microscope (TEM). It is found that an increased carbon content enhances the dynamic flow resistance of the three steels. Additionally, the flow stress increases with strain and strain rate in every case. A thermal softening effect is identified in the plastic behaviour of the three steels. The activation energy, ΔG *, varies as a function of the strain rate and temperature, but is apparently insensitive to the carbon content level. The present study identifies maximum ΔG * values of 58kJ/mol for the S15C low carbon steel, 54.9kJ/mol for the S50C medium carbon steel, and 56.4kJ/mol for the SKS93 high carbon steel. A Zerilli–Armstrong BCC constitutive model with appropriate coefficients is applied to describe the high strain rate plastic behaviours of the S15C, S50C and SKS93 steels. The errors between the calculated stress and the measured stress are found to be less than 5%. The microstructural observations reveal that the dislocation density and the degree of dislocation tangling increase with increasing strain rate in all three steels. Additionally, the TEM observations indicate that a higher strain rate reduces the size of the dislocation cells. The annihilation of dislocations occurs more readily at elevated temperatures. The square root of the dislocation density increases linearly with the work hardening stress. The current results provide a valuable reference for the application of S15C low carbon steel, S50C medium carbon steel, and SKS93 high carbon steel in high-speed plastic forming processes. [Copyright &y& Elsevier]

Abstract: This study employs a compressive split-Hopkinson bar to investigate the plastic deformation behaviour of Inconel 690 super alloy when subjected to high temperature and high-strain-rate loading conditions. Dynamic impact testing is performed under strain-rates ranging from 2.3×103 to 8.3×103 s−1 at temperatures between 25 and 900°C. Optical, scanning, and transmission electron microscopy techniques are used to analyze the fracture and microstructure characteristics of the deformed specimens in order to determine the relationship between the alloy''s mechanical and microstructural properties. The experimental results indicate that temperature, strain and strain rate influence the material''s mechanical properties. At constant temperature, the flow stress, and strain-rate sensitivity both increase with increasing strain rate, but the activation volume and work hardening coefficient decrease. Meanwhile, at a constant strain rate, the flow stress, strain-rate sensitivity and work hardening coefficient decrease with increasing temperature, but the activation volume and temperature sensitivity increase. Shear band formation is followed by fracture characterized by dimpled structures. Microscopy yields evidence of dislocation and twinning. The dislocation and twinning densities increase with increasing strain-rate and flow stress, but decrease with increasing temperature. It is shown that the Zerilli–Armstrong constitutive equation with experimentally determined specific material parameters successfully describes the flow behaviour of the Inconel 690 super alloy under the current test conditions. [Copyright &y& Elsevier]

Abstract: Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We proposed a novel tunable field-sensitive polarizer based on conventional waveguides and PC structures with nematic liquid crystals. Its properties were investigated numerically by using the plane wave expansion method and finite-difference time-domain method. The bandgaps can be continuously modulated after infiltrating nematic liquid crystals into the PC structure. Then the polarizer can separate TM- and TE-polarized modes in the waveguide. These results may provide novel application of polarizer in photonic integrated circuits. [Copyright &y& Elsevier]

Abstract: Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. In this paper, the influence of interaction region of elliptical pillars on a directional photonic crystal waveguide coupler is studied by solving Maxwell''s equations with use of finite-difference time-domain method. The PC waveguide coupler introduced two rows of elliptical pillars in the interaction region. Introducing elliptical pillars in the interaction region can reduce the coupling length of PC waveguide coupler. The coupling length of PC waveguide coupler was changed by rotating the rotation angle of elliptical pillars. These results may provide novel application in photonic integrated circuits. [Copyright &y& Elsevier]

The dynamic impact deformation behavior, fracture characteristics and microstructural evolution of Inconel 690 alloy under high rate loading conditions are studied. Mechanical impact tests are performed at strain rates ranging from 2.3×103 to 8.3×103 s-1 at room temperature by compressive split-Hopkinson bar. The effects of strain rate on dynamic flow response, work hardening characteristics, strain rate sensitivity and thermal activation volume are evaluated. A constitutive law is proposed, based on the Zerilli–Armstrong model. Evolutions of dislocation and twins substructures are investigated using transmission electron microscopy. Relationships between flow stress, dislocation and twinning are analyzed and discussed in terms of loading conditions. Scanning electron microscopy is used to evaluate damage initiation and fracture mechanisms. The observed flow stress–strain response is influenced greatly by strain rate, resulting in obvious change of work hardening rate, strain rate sensitivity, activation volume, and also dislocation tangle and deformation twin substructures. Catastrophic failure at high rate results from the formation of localized shear bands. The proposed constitutive law describes the observed response quite well. [Copyright &y& Elsevier]

Poly(methyl methacrylate) (PMMA) exhibits significantly tacticity-dependent properties, e.g. the glass transition temperature (T g), the characteristic ratio (C ∞), the specific volume and the gas permeability coefficient. Syndiotactic (s) PMMA is the most peculiar, exhibiting complex α - β relaxations. We first make brief reviews about key experimental facts of s -PMMA relaxations: 1) unusual α - β split; 2) tacticity dependence of T g ; 3) discrepancy between chain stiffness and T g. Based on the chain conformation analysis of Vacatello and Flory in 1986, and combined with the experimental results from dielectric spectroscopy (DS), dynamic-mechanical analysis (DMA), nuclear magnetic resonance (NMR), we have demonstrated that the molecular origin of the peculiar α - β relaxations resulted from the all-trans extended conformations which are predominant in syndiotactic PMMA. This local extended (and curved) structure, as a bigger jumping unit, induces the formation of domains with slow dynamics. The percolation of slow domains causes the freezing of the large-amplitude motion of main chains, and then a novel α transformation occurs at a higher temperature eventually. The high-specific volume state below T g provides a space for the constraint rotation of ester groups, showing a strong β relaxation even far from the T g. Therefore, many related experimental phenomena, e.g. the tacticity-dependence of properties, the effect of α- methyl, the effect of side-chain n-alkyl, the effect of molecular weight, and otherwise are easily resolved. Since adjacent bond angles are unequal in all-trans extended conformations, the backbone is curved, hence the s -PMMA chain tends to form quasi-cyclic structure, leading to the reversely correlation between the overall chain size (C ∞) and the local stiffness (T g). Lastly, the impact of these findings on the glass theory is presented in conclusions. [Display omitted] • Molecular origin of the peculiar α - β relaxations results from the all-trans extended conformationsin s -PMMA. • The local extended -structure, as a bigger jumping unit, induces the formation of domains with slow dynamics. • The local stiffness instead of the overall chain size determines the occurrence of the glass transition. • Molecular image of s -PMMA relaxations provides insights to understand the precise nature of the glass transition. [ABSTRACT FROM AUTHOR]

Competition for nest site resources among sympatric bird species leads to differences in occupying superior resources, which can directly influence their breeding performance. However, how sympatric congeneric bird species alleviate interspecific competition in nest site selection and achieve coexistence remains unclear. Therefore, we conducted a long-term investigation on the nest site selection and breeding performance of two sympatric congeneric species, Scaly-breasted Munia (Lonchura striata) and White-rumped Munia (Lonchura punctulata) in Xishuangbanna, Yunnan Province, southwest China, from 2017 to 2021. Our findings revealed that White-rumped Munia and Scaly-breasted Munia shared overlapped breeding period, but had significant spatial segregation. Regarding the impact of nest site selection on the breeding performance of these two bird species, we found that increasing nest concealment led to higher nestling numbers, fledgling numbers, and breeding success rate. Conversely, greater proximity to nests of heterologous species was correlated with reduced nestling numbers, hatching rates, and breeding success rates. Additionally, nests located in closer proximity to water edges exhibited reduced fledgling numbers, whereas choosing trees with larger diameter at breast height positively correlated with higher fledgling numbers. Compared to White-rumped Munia, Scaly-breasted Munia were inclined to occupy more concealed nests, tree with larger diameters, and closer to heterologous nests. Therefore, the nestling numbers, the fledgling rate, and the breeding success rate of the Scaly-breasted Munia were significantly higher than those of the White-rumped Munia. This study further showed that the increase of nest concealment and decrease of nearest distance to the nest of heterologous species decreased nest predation rate, therefore, increased the breeding success rate. Our study unveiled that, by spatial segregation and different nest site selection, two sibling bird species with highly overlapped breeding period can achieve coexistence in tropical areas. • White-rumped Munia and Scaly-breasted Munia shared overlapped breeding period in tropical area. • These two munias had significant spatial segregation. • Nest site selection influenced the breeding performance of these two munias. • The two congeneric munia species achieved coexistence by spatial segregation through nest site selection. [ABSTRACT FROM AUTHOR]

According to the Kamlet-Abraham-Taft (KAT) polarity parameters (α, β, π*), polymers and solvents can be categorized as hydrogen-bond (H-bond) acidic (α>β) or H-bond basic (α<β). Recently, we proposed a quantitative hydrogen bonding (QHB) analysis to predict the solubility of polymers in ionic liquids (ILs) using the product of ΔαΔβ<0 as an indicator, where Δα is the difference between the H-bond acidic parameters of the polymer and IL, and Δβ is the difference in their basicity, while the prerequisite of the "complementary" principle (i.e., that one component is H-bond acidic and the other is basic) is satisfied. Here, the applicability of QHB analysis was first confirmed by testing the solubilities of carefully chosen polymer/deep eutectic solvent (DES) pairs, as the DESs were eutectic mixtures dominated by hydrogen bonding interactions. Then, our attention focused on the solubility of cellulose in DESs. Our testing results as well as the typical published results were summarized, which indicate that the potential DESs for cellulose dissolution and regeneration must be of the H-bond basic type because the "complementary" principle should be satisfied as a prerequisite. However, the H-bond basic DESs investigated in this study do not show the superior solubility of cellulose that has been commonly observed for H-bond basic ILs, even if the criterion of ΔαΔβ<0 is satisfied for both DESs and ILs. Possible reasons for this discrepancy are given to understand the varying effectiveness in cellulose dissolution for H-bond basic DESs and ILs. [ABSTRACT FROM AUTHOR]

[Display omitted] • NO 3 −-N, NO 2 −-N, NH 4 +-N, OM, TN, EC and Cl− showed a leaching dynamic along depths. • Cl− was significantly positively correlated with TN, NH 4 +-N, OM, NO 3 −-N and EC. • TN, NH 4 +-N, OM, NO 3 −-N, and EC were used as characteristic pollutants. • NO 3 −-N, NH 4 +-N, NO 2 −-N, SO 4 2−, pH and EC greatly affected microbial communities. • Hydrogenispora and Caldicoprobacter were selected as characteristic microorganisms. Leachate leakage poses a serious environmental risk to the safety of surrounding soils and groundwater. A much faster approach to reflect landfill leakage is the premise to mitigate the ecological risk of landfills. In this study, two landfills (BJ and WZ) were selected to investigate the leaching characteristics of various pollutants along the vadose soil depths. The physiochemical properties of underlying soils including NO 3 −-N, NO 2 −-N, NH 4 +-N, OM, TN, EC and Cl− exhibited a typical leaching dynamic along the depths. Among them, TN, NH 4 +-N, OM, NO 3 −-N, and EC might be used as characteristic pollutants to evaluate the leachate leakage issues in landfilled sites. The genera Thiopseudomonas , Acinetobacter , Pseudomonas , and Hydrogenispora dominated in underlying soils. Compared to BJ samples, a more diverse and active microbiome capable of carbon and nitrogen cycles was observed in WZ samples, which was mainly ascribed to nutrients and elements contained in different types of soils. Among the environmental factors, nitrogenous compounds, SO 4 2−, pH and EC had significant effects on the microbial community structures in the underlying soils. The relative abundances of Hydrogenispora and Caldicoprobacter might be used as characteristic microorganisms to evaluate the leachate leakage issues in landfilled sites. These results provided a deep insight into effects of leachate leakage in underlying soils, especially the pollutants vertical distribution and the corresponding microbial community structures. [ABSTRACT FROM AUTHOR]

Superelastic, arbitrary‐shaped, and 3D assembled clay/graphene aerogels (CGAs) are fabricated using commercial foam as sacrificial skeleton. The CGAs possess superelasticity under compressive strain of 95% and compressive stress of 0.09–0.23 MPa. The use of clay as skeletal support significantly reduces the use of graphene by 50%. The hydrophobic CGAs show high solvent absorption capacity of 186–519 times its own weight. Moreover, both the compression and combustion methods can be adopted for reusing the CGAs. In particular, it is demonstrated a design of 3D assembled hydrophilic CGA equipped with salt collection system for continuous solar desalination. Due to energy recovery and brine transport management promoted by this design, the 3D assembled CGA system exhibits an extremely high evaporation rate of 4.11 kg m−2 h−1 and excellent salt‐resistant property without salt precipitation even in 20 wt% brine for continuous 36 h illumination (1 kW m−2), which is the best reported result from the solar desalination devices. More importantly, salts can be collected conveniently by squeezing and drying the solution out of the salt collection system. The work provides new insights into the design of 3D assembled CGAs and advances their applications in continuous solar desalination and efficient oil/organic solvent adsorption. [ABSTRACT FROM AUTHOR]

In this paper, AlN films grown by magnetron sputtering method have been proposed as the gate insulator layer of AlGaN/GaN high electron mobility transistors (HEMTs) to decrease gate leakage current and suppress the interface trap. The effect of the temperature of substrate on the quality of AlN films have been investigated. By inserting the thin AlN film (35 nm) as a gate insulator layer, the on-state resistance of AlGaN/GaN HEMTs decrease from 11.1 Ω mm to 10.3 Ω mm @ V g = 0 V, the current collapse decreases from 16.6% to 3.2%, the gate leakage can be reduced from 1.2 Ă— 10âˆ'1A mmâˆ'1 to 4.4 Ă— 10âˆ'6A mmâˆ'1 @ V g = 2 V by five orders of magnitude, and the fast interface states disappear and the normal trap density decreases from 0.96â€"1.3 Ă— 1013 cmâˆ'2eVâˆ'1 to 1.3â€"3.4 Ă— 1012 cmâˆ'2 eVâˆ'1, proving that magnetron-sputtered AlN is an effective way to improve the performance of GaN HEMTs. [ABSTRACT FROM AUTHOR]

In concentrated polymer solutions,the concentration (ϕ) dependence of the terminal relaxationtime τdreflects ϕ-dependent changes of severalfactors, the monomeric friction ζ0(ϕ), theentanglement length, a(ϕ), and the correlationlength, ξ(ϕ). Usually, the effect of the latter two factorson τdcan be cast in a simple power law, τd∼ ϕv. This powerlaw form is to be examined for τdafter correctionof the changes of ζ0with ϕ, but this iso-ζ0correction is an unsettled problem. The correction basedon the concept of “iso-free-volume” has been attemptedin literatures. This study focused on four groups of solutions withdifferent local frictional environments to examine universal validityof this correction. The isothermal data of τdwererheologically measured, and then corrected to the iso-frictional (iso-ζ0) state. After this correction, τdof mostsolutions in small molecule solvents showed the power law behaviorτd∼ ϕvwithexponent of v= 2.0 ± 0.2, irrespective of thesolvent type, either neutral small molecules or an ionic liquid (organicsalt), and of the difference of the glass transition temperaturesof the solvent and polymer. In contrast, the exponent became smaller(v≈ 1.3) for the solutions in an oligomericsolvent. These results are discussed within the frame of the two-lengthscaling theory that considers changes of ξ and awith ϕ. [ABSTRACT FROM AUTHOR]

Test methods including OM, SEM, TEM, DSC, SAXS, WAXS, and IR were used to characterise supra-molecular structure in three batches of polyethylene (PE), which had weight-average relative molar masses M ¯ w ${\overline{M}}_{\text{w}}$ of approximately 0.6 × 106, 5 × 106, and 9 × 106. They were applied to compression mouldings made by the polymer manufacturer. Electron microscopy showed that powders formed in the polymerization reactor consisted of irregularly shaped grains between 50 and 250 μm in diameter. Higher magnification revealed that each grain was an aggregate, composed of particles between 0.4 and 0.8 μm in diameter, which were connected by long, thin fibrils. In compression mouldings, lamellar thicknesses ranged from 7 to 23 nm. Crystallinity varied between 70 and 75 % in reactor powder, but was lower in compression mouldings. Melting peak temperatures ranged from 138 to 145 °C, depending on processing history. DMTA showed that the glass transition temperature θg was −120 °C for all three grades of polyethylene. IR spectroscopy found negligibly small levels of oxidation and thermal degradation in mouldings. Optical microscopy revealed the presence of visible fusion defects at grain boundaries. It is concluded that relatively weak defects can be characterized using optical microscopy, but there is a need for improved methods that can detect less obvious fusion defects. [ABSTRACT FROM AUTHOR]

The aim of this project was to study the efficacy of current methods of quality control and quality assurance for ultra-high molecular weight polyethylene (UHMWPE) products, and find improvements where possible. Intrinsic viscosity (IV) tests were performed on three grades of polyethylene with weight average relative molar masses M ̅ $̅{M}$ w of about 6 × 105, 5.0 × 106 and 9.0 × 106. Results from three laboratories showed substantial scatter, probably because different methods were used to make and test solutions. Tensile tests were carried out to 600 % extension at 150 °C under both constant applied load and constant Hencky strain rate, on compression mouldings made by a leading manufacturer of ultra-high molecular weight polyethylene. They gave low values of M ̅ $̅{M}$ w, suggesting incomplete entanglement at 'grain boundaries' between powder particles. Results from conventional melt-rheology tests are presented, and their relevance to quality control and assurance is discussed. Attempts to calculate molecular weights from these data met with limited success because of extended relaxation times. Suggestions are made for improving international standards for IV testing of UHMWPE, by investigating the various factors that can cause significant errors, and by introducing methods for checking the homogeneity (and hence validity) of the solutions tested. Part 2 addresses characterization of crystallinity and structure. Part 3 covers mechanical properties, and Part 4 focuses on the sporadic crack propagation behaviour exhibited by all three grades of UHMWPE in fatigue tests on 10 mm thick compact tension specimens. [ABSTRACT FROM AUTHOR]

Three grades of polyethylene, with weight-average relative molar masses, M ‾ W ${\bar{M}}_{\text{W}}$ , of approximately 0.6 × 106, 5 × 106, and 9 × 106, were supplied as compression mouldings by a leading manufacturer of ultra-high molecular weight polyethylene (UHMWPE). They were code-named PE06, PE5, and PE9, respectively. Specimens cut from these mouldings were subjected to a wide range of mechanical tests at 23 °C. In tensile tests, deformation was initially elastic and dominated by crystallinity, which was highest in PE06. Beyond the yield point, entanglement density became the dominant factor, and at 40 % strain, the rising stress–strain curves for PE5 and PE9 crossed the falling PE06 curve. Fracture occurred at strains above 150 %. Differences in stress–strain behaviour between PE5 and PE9 were relatively small. A similar pattern of behaviour was observed in wear tests; wear resistance showed a marked increase when M ‾ W ${\bar{M}}_{\text{W}}$ was raised from 0.6 × 106 to 5 × 106, but there was no further increase when it was raised to 9 × 106. It is concluded that the unexpected similarity in behaviour between PE5 and PE9 was due to incomplete consolidation during moulding, which led to deficiencies in entanglement at grain boundaries; they were clearly visible on the surfaces of both tensile and wear specimens. Fatigue crack growth in 10 mm thick specimens was so severely affected by inadequate consolidation that it forms the basis for a separate report – Part 4 in this series. [ABSTRACT FROM AUTHOR]

Fatigue tests were carried out on compression mouldings supplied by a leading polymer manufacturer. They were made from three batches of ultra-high molecular weight polyethylene (UHMWPE) with weight-average relative molar masses, M ¯ W ${\overline{M}}_{\mathrm{W}}$ , of about 0.6 × 106, 5 × 106 and 9 × 106. In 10 mm thick compact tension specimens, crack propagation was so erratic that it was impossible to follow standard procedure, where crack-tip stress intensity amplitude, ΔK, is raised incrementally, and the resulting crack propagation rate, da/dN, increases, following the Paris equation, where a is crack length and N is number of cycles. Instead, most of the tests were conducted at fixed high values of ΔK. Typically, da/dN then started at a high level, but decreased irregularly during the test. Micrographs of fracture surfaces showed that crack propagation was sporadic in these specimens. In one test, at ΔK = 2.3 MPa m0.5, there were crack-arrest marks at intervals Δa of about 2 μm, while the number of cycles between individual growth steps increased from 1 to more than 1000 and the fracture surface showed increasing evidence of plastic deformation. It is concluded that sporadic crack propagation was caused by energy-dissipating crazing, which was initiated close to the crack tip under plane strain conditions in mouldings that were not fully consolidated. By contrast, fatigue crack propagation in 4 mm thick specimens followed the Paris equation approximately. The results from all four reports on this project are reviewed, and the possibility of using fatigue testing as a quality assurance procedure for melt-processed UHMWPE is discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper uses a compressive split-Hopkinson bar and transmission electron microscopy (TEM) to investigate the impact properties and residual microstructures of Plasma Arc Welded 304L SS weldments. The current specimens were fabricated using either a continuous current (CC) or a pulsed current (PC) welding mode and were then deformed at strain rates ranging from 10−3 s−1 to 7.7×103 s−1 at room temperature. The impacted specimens were polished and etched and then analysed using TEM to investigate the correlation between their dynamic mechanical response and the microstructural evolution of dislocations, mechanical twins and α′ martensite structures. The results showed that the microstructural characteristics of the weldments were influenced both by the strain rate and by the welding current mode. Comparing the evolution of the microstructure in the base metal and the fusion zone, it was found that a higher dislocation density existed in the fusion zone, while a larger volume fraction of α′ martensite and a greater twinning density were present in the base metal. Furthermore, for both welding current modes, the dislocation density and volume fraction of α′ martensite were found to increase with increasing strain rate, whereas the twinning density reduced. Microstructural analysis revealed that the number of dislocations, twins and α′ martensite structures varied as an increasing function of the work-hardening stress. Finally, it was determined that the microstructure of the PC weldments enhanced the dynamic impact response. [Copyright &y& Elsevier]

Abstract: This paper presents an investigation into the high velocity impact of 304L stainless steel gas tungsten arc welded (GTAW) joints at strain rates between 10−3 and 7.5×103 s−1 using a compressive split-Hopkinson bar. The results show that the impact properties and fracture characteristics of the tested weldments depend strongly on applied strain rate. This rate-dependent behavior is in good agreement with model predictions using the hybrid Zerilli–Armstrong constitutive law. It is determined that the tested weldments fail as a result of adiabatic shearing. The fracture surfaces of the fusion zone and base metal regions are characterized by the presence of elongated dimples. The variation in the observed dimple features with strain rate is consistent with the results of the impact stress–strain curves. [Copyright &y& Elsevier]

To improve the photocatalytic activity of TiO2 film, Ti substrates are irradiated by He ions with different incident ion energy, temperature, and fluence. Anatase TiO2 films are then coated on the plasma-irradiated substrates via chemical vapor deposition followed by calcination. Photocurrent tests and photocatalytic oxidation (PCO) of formaldehyde are used to assess photocatalytic performance. The optimal plasma-irradiated samples showed a four times higher photocurrent and a three fold increase in the rate constant of the PCO reaction compared to the TiO2 coated, untreated control sample. It is found that the enhanced photocatalytic activity and photocurrent are related to the changes of Ti crystal structure and surface morphology through plasma irradiation. [ABSTRACT FROM AUTHOR]

A PDMS elastomer based on acylhydrazone groups with both acid- and heat-assisted self-healing properties was successfully prepared from tetra-acylhydrazine-terminated PDMS and terephthalaldehyde through solution casting. The good healing performance was obtained with catalytic acetic acid for 24 h at 25 °C or by annealing at 120 °C for 2 h. The elastomer exhibited a reversible transition near 80 °C observed by rheological measurements and variable-temperature FTIR, which corresponded to the dissociation and reconstruction of hydrogen bonds between acylhydrazone groups. Since the non-equimolar sample presented similar behaviors with the equimolar sample, it verifies that the reversible dissociation/reformation of hydrogen bonds dominates the heat-assisted self-healing process. This finding will enable better understanding of the contribution of hydrogen bonding interactions in acylhydrazone self-healing systems, thus promoting the development of self-healing bulk materials based on acylhydrazone groups. [ABSTRACT FROM AUTHOR]

In this paper, the reversible crystal-crystal transition of poly(hexamethylene dithiocarbonate) (PHMDC) has been systematically studied. According to various experimental results, we confirm that the transition shares the common features with Brill transition that is widely observed in nylons. This transition is clearly associated with the reversible trans - gauche conformational transformation of the methylene sequences in the crystal lattice. Therefore, in addition to its analogue poly(octamethylene carbonate) POMC ( ACS Macro Lett . 2015, 4, 317–321), PHMDC can be considered as a new example of the polymers exhibiting Brill transition outside the nylon family. Careful examination of the experimental data reveals that for PHMDC the enthalpy ratio of the Brill transition to the melting is a constant of ∼2/3, independent of the crystallization condition applied. Furthermore, the difference between the Brill transition temperatures determined from heating and cooling is also a constant, which is of ∼4 °C. These new observations are obtained because the Brill transition of PHMDC is sharp and possesses a large transition enthalpy. Such a transition is associated with that the methylene segments in PHMDC can change their conformation between trans and gauche rapidly and completely in a narrow temperature interval. [ABSTRACT FROM AUTHOR]

The thermal imidization process of 1,2,4,5-benzenetetracaboxylic (PMDA)/4,4’-diamnodiphenyl ether (4,4′-ODA) solutions in N -methyl-2-pyrrolidone (NMP) from polyimide (PI) precursor, poly (amic acid) (PAA), was systematically investigated through a series of characterization methods, such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). At the low-temperature drying stage, mechanical properties and T g of polymer films were increased as a result of solvent removal. TGA method was used to quantitatively monitor the evaporations of hydrogen-bonded solvents on PAA and of the dehydration during the imidization reaction that occurred above 150 °C. During the imidization stage, the interplay between the solvent evaporation and the imidization was the key factor that determined the enhancement of the mechanical properties and T g . The degree of imidization approached 94% when the temperature was increased to 250 °C. A “complete” imidization was achieved by annealing between 350 and 400 °C. The enhancement in the mechanical properties of final PI films may result from the increased T g and the crystallized structure formed during the annealing stage. [ABSTRACT FROM AUTHOR]

Landfills are the third largest source of anthropogenic CH 4 emissions. Anaerobic oxidation of methane (AOM) activity and communities of methane-oxidizing bacteria were investigated in three informal landfills in this study, namely, BJ, CH and SZ landfills, among which BJ and CH represent traditional anaerobic landfills, while the SZ landfill was subjected to aeration to accelerate waste stabilization. The AOM rates of the investigated landfilled wastes ranged from 3.66 to 23.91 nmol g−1 h−1. Among the three landfills, the AOM rate was highest in the SZ-1-Top sample, which was closest to the aeration pipe. Among the possible electron acceptors for AOM, including NO 3 −, NO 2 −, SO 4 2− and Fe3+, the NO 2 −-N content was the only variable that was positively correlated with the AOM rate. Compared with α- Proteobacteria methanotrophs, γ- Proteobacteria methanotrophs were more abundant in the landfilled waste, especially Methylobacter, which was detected in nearly all samples. Members of the family Methylomirabilaceae, including Candidatus Methylomirabilis, were also detected in the SZ-1 and SZ-2-Bot samples. The relative abundance of the main methanotrophs in the families Methylomonadaceae, Methylococcaceae , Rokubacteriales and Methylomirabilaceae , the genus Methylocystis and the phylum NC10 were all positive correlations with the contents of NO 2 −-N in the landfilled waste samples. Additionally, significantly positive correlations were observed between the AOM rates and the relative abundance of the main methanotrophs except for the family Methylococcaceae. This indicated that aeration could enhance the conversion of nitrogen compounds in the landfilled waste, in which the high contents of NO 2 −-N could stimulate the growth of methanotrophs and increase AOM rate. These findings are helpful for understanding the mechanisms of CH 4 oxidation in landfills and for taking effective measures to mitigate CH 4 emissions from landfills. • Aeration could enhance the AOM activity of landfilled waste. • NO 2 −-N content of landfilled waste had a positive relationship with AOM rate. • TS, NH 4 +-N, TN were the main factors affecting microbial community in landfills. • Methylobacter was rich in nearly all the landfilled waste samples. • NO 2 −-N content was positively related with the relative abundance of methanotrophs. [ABSTRACT FROM AUTHOR]

A new class of peripherally multiple aromatic ester-functionalized poly(benzyl ether) dendrons and/or dendrimers with different focal point substituents, surface groups, interior structures, as well as different generations have been synthesized and their structure-property relationships with respect to their gelation ability have been investigated systematically. Most of these dendrons are able to gel organic solvents over a wide polarity range. Evident dendritic effects were observed not only in gelation capability but also in thermotropic, morphological, and rheological characterizations. It was disclosed that subtle changes in peripheral ester functionalities and interior dendritic structures affected the gelation behavior of the dendrons significantly. Among all the dendrons studied, the second- and third-generation dendrons G0G2-Me and G0G3-Me with dimethyl isophthalates (DMIP) as peripheral groups exhibited the best capability in gelation, and stable gels were formed in more than 22 aromatic and polar organic solvents. The lowest critical gelation concentration (CGC) reached 2.0 mg mL−1, indicating that approximately 1.35×104 solvent molecules could be entrapped by one dendritic molecule. Further study on driving forces in gel formation was carried out by using a combination of single-crystal/powder X-ray diffraction (XRD) analysis and concentration-dependent (CD)/temperature-dependent (TD) 1H NMR spectroscopy. The results obtained from these experiments revealed that the multiple π-π stacking of extended π-systems due to the peripheral DMIP rings, cooperatively assisted by non-conventional hydrogen-bonding, is the key contributor in the formation of the highly ordered supramolecular and fibrillar network. In addition, these dendritic organogels exhibited unexpected thixotropic-responsive properties, which make them promising candidates with potential applications in the field of intelligent soft materials. [ABSTRACT FROM AUTHOR]

A new class of poly(aryl ether) dendritic ligands containing a pyridine functionality at the focal point and the corresponding AgI complexes through metal-ligand coordination were designed, synthesized, and fully characterized. Compared with the dendritic ligands, the corresponding dendritic complexes exhibited much better gelation ability for various organic solvents at very low critical gelation concentrations. The gel-sol phase transition temperatures and morphologies could be finely tuned by binding silver ion to the ligand. A preliminary study revealed that multiple noncovalent interactions, such as AgI-pyridine coordination, solvophobic interaction, and π-π stacking, synergistically enable the formation of stable metallogels. Interestingly, these metallogels could intelligently respond to multiple external stimuli including temperature, chemicals, and shear stress, leading to gel-sol phase transitions. In addition, these dendritic metallogels were successfully applied as templates for the in situ formation and stabilization of silver nanoparticles without the use of any chemical reducing/stabilizing agents. [ABSTRACT FROM AUTHOR]

Abstract: A supramolecular polymer gel formed between triptycene-based bis(crown ether) and copolymer containing dibenzylammonium (DBA) moieties by host–guest interactions was described. We demonstrated the formation of the supramolecular polymer networks between the bis(crown ether) and the copolymer by the 1H NMR spectroscopy and solution viscometry, and we also obtained a colorless and transparent supramolecular polymer gel at high concentration. Moreover, the supramolecular polymer gel showed multi-stimuli reversible responsiveness, such as thermo-, acid/base-, and chemo- induced gel–sol transitions. Furthermore, the result of rheological measurements showed the gel has an intrinsic self-healing property, and the thixotropic process could be repeated at least three times. Interestingly, when doped with spiropyran molecules, the supramolecular polymer gel could also be employed as erasable materials. Thus, these results could be highly anticipated to benefit for further construction of smart materials with high healing efficiency, and ultimately be used in practical application. [Copyright &y& Elsevier]

A new class of poly(benzyl ether) dendrimers, decorated in their cores with N-Boc-protected 1,2-diphenylethylenediamine groups, were synthesized and fully characterized. It was found that the gelation capability of these dendrimers was highly dependent on dendrimer generation, and the second-generation dendrimer ( R, R)-G2DPENBoc proved to be a highly efficient organogelator. A number of experiments (SEM, TEM, FTIR spectroscopy, 1H NMR spectroscopy, rheological measurements, UV/Vis absorption spectroscopy, CD, and XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels. The hydrogen bonding, π-π, and solvophobic interactions were found to be the main driving forces for formation of the gels. Most interestingly, these dendritic organogels exhibited smart multiple-stimulus-responsive behavior upon exposure to environmental stimuli such as temperature, anions, and mechanical stress. [ABSTRACT FROM AUTHOR]

A new poly(benzyl ether) dendritic organogelator Azo-G3containing azobenzene in its inner layer was designed and synthesized,and fully characterized. The dendron Azo-G3 was found to be a highlyefficient and versatile organogelator toward various apolar and polarorganic solvents with the critical gelation concentrations (CGCs)approaching 0.05 wt %, indicating that the dendron belongs to thecategory of supergelators. Further studies revealed that the intermolecularmultiple π–π stacking interactions might be responsiblefor guiding the self-assembly processes and the gel formation. Mostinterestingly, these dendritic organogels exhibited multiple stimuli-responsivebehaviors upon exposure to environmental stimuli including temperature,sonication, light, and shear stress. [ABSTRACT FROM AUTHOR]

Abstract: Rheological properties of cellulose dissolved in two ionic liquids (ILs), 1-allyl-3-methylimidazolium chloride (AmimCl) and 1-butyl-3-methylimidazolium chloride (BmimCl), with co-solvent dimethylsulfoxide (DMSO), are studied in the concentration range of cellulose from 0.070 to 6.0 wt%. The viscosities of ILs are exponentially decreased by adding DMSO in the concentration range of 0–100 wt%. The co-solvent DMSO decreases the monomer friction coefficient in cellulose solutions and has no significant change for the entanglement state of cellulose, thus results in the reduced solution viscosity, shortened relaxation time and unchanged moduli of the cross-over point. For cellulose solutions, dilute regime, semidilute unentangled regime and semidilute entangled regime were determined by steady shear experiments. In semidilute entangled regime, the specific viscosities η sp, relaxation time τ, and plateau modulus G N, exhibit concentration dependences as η sp ∼ C 4.4, τ ∼ C 2.2, andG N ∼ C 1.9, respectively, in AmimCl-DMSO (80/20 w/w); and η sp ∼ C 4.3, τ ∼ C 2.0, and G N ∼ C 2.1, respectively, in BmimCl–DMSO (80/20 w/w). Therefore, the rheological properties of cellulose/IL/DMSO solutions are approximately of IL-independence in this study. The dependence of η sp upon cellulose concentration shows that the IL–DMSO mixture is more like a θ solvent for cellulose, and the thermodynamic properties of IL–DMSO mixtures are similar with those of ILs for cellulose at 25 °C. The conformation of cellulose in ILs would not be changed with the addition of DMSO not only in the dilute regime but also in the entanglement regime. [Copyright &y& Elsevier]

The master curves of a series of aliphatic polycarbonates (APCs) with different lengths of methylene segments in the repeat unit were obtained by dynamic rheological measurements. The plateau modulus and entanglement molecular weight were determined and cross-checked by different methods. Though having distinct difference in chemical structure of repeat units, both APCs and bisphenol-A polycarbonates have the similar entanglement weight and entanglement spacing. On the other side, the plateau modulus decreases with increasing the length of the side group of aliphatic polycarbonates with different side-chain lengths in the literature. The packing length model can explain the relationship between chain structure and entanglements. [ABSTRACT FROM AUTHOR]

In our previous work [Macromolecules2010, 43, 1191–1194], we synthesizeddynamiccovalent cross-linked polymer gels through condensation of acylhydrazinesat the chain ends of poly(ethylene oxide) (A2) and aldehydegroups in tris[(4-formylphenoxy)methy]ethane (B3) and reportedreversible sol–gel transition and self-healing properties ofthe gels. For those dynamic gels, this paper examines the gelationkinetics and rheological behavior in pre- and postgelation stagesand discusses the molecular mechanism underlying the mechanical andself-healing properties. The results showed that the condensationreaction before the critical gelation point can be treated as thepseudo-second-order reaction. The scaling exponent n(=0.75) for the frequency dependence of the complex moduli at thecritical gel point, the exponent γ (=1.5) for the concentrationdependence of the viscosity in the pregel regime, and the exponent z(=2.5) for the concentration dependence of the equilibriummodulus in the postgel regime were found to not exactly obey the relationshipfor covalent gels, n= z/(z + γ), possibly because of the dynamic nature ofthe gels. The terminal relaxation of the dynamic gels at high temperature(125 °C) accorded with the Maxwellian model, as often observedfor transient associating networks. In contrast, at low temperature(25 °C) where this transient network reorganization was essentiallyquenched in a time scale of experiments (∼50 s), the uniaxialstress–strain behavior of the gel was well described by theclassical model of rubber elasticity σeng= G(λ – 1/λ2) up to 300% stretch(as similar to the behavior of usual gels chemically cross-linkedin a swollen state). Ultimately, the gel cut into two pieces was foundto exhibit self-healing under ambient conditions in 8 and 24 h, respectively,when the edges of those pieces were coated and not coated with acid(catalyst for dynamic covalent bond formation). [ABSTRACT FROM AUTHOR]

We investigate the linear and non-linear rheological behavior in shear of a concentrated solution of 'dumbbell' polystyrene with long linear backbone and dense short brushes at both ends and compare it with corresponding linear polymers. This type of dumbbells has never been rheologically characterized before. In linear viscoelasticity, the dumbbell polymers show significant differences with conventional linear polymers. In particular, the reptation relaxation of the dumbbell is strongly slowed down. Furthermore, the addition of the side chains increases the friction so that the dumbbell lies above the η vs. number of entanglements relation of linear samples. Transient shear rheology experiments on weakly entangled solutions show a retardation of the chain stretch relaxation of the dumbbell by a factor 2.5 vs. a linear polymer with the same Rouse time. Additionally, a second peak in the transient viscosity is observed at high shear rates. [ABSTRACT FROM AUTHOR]

Dependence of the nonlinear and linear viscoelastic behaviors of thermoplastic vulcanizates (TPV) on the content (φ) of rubber nanoparticle agglomerates (NPAs) was explored by dynamic oscillation shear tests. Under a large strain, TPV exhibit a φ -dependent yield stress ( σ y ) as σ y ∝ φ 1.53 ± 0.87 . As φ increases, the rubber NPAs network becomes stronger, and the elastic modulus and viscosity of TPV increase. φ -dependent modulus ( G 0 ' ) of TPV is G 0 ' ∝ φ 3.18 ± 0.24 in the low- ω region. Rubber NPs agglomerate to form a network more easily than rigid particles. The fractal dimension d f (=1.65 ± 0.09) of the rubber NPAs in TPV is lower than the universal d f (~1.8) of rigid particles aggregates. The φ -dependent modulus G 0 ' of TPV in the linear viscoelastic region shows G 0 ' ~ { ( φ c − φ) 1 , f o r i s o l a t e d r u b b e r N P A s , φ ≤ φ c (φ − φ c ) 2.15 ± 0.12 , f o r r u b b e r N P A s n e t w o r k , φ ≥ φ c , where φ c is the percolation threshold of φ. This study provides an understanding of the viscoelasticity of TPV containing rubber NPAs and their network structure. Image 1 • Viscoelasticity of TPVs containing rubber nanoparticles agglomerates (NPAs) was disclosed. • TPVs containing rubber NPAs network exhibit a strong stress overshoot, as a yield stress fluid. • Rubber nanoparticles agglomerate to form a network more easily than rigid particles. • Dependence of the viscoelasticity of TPVs on content of rubber NPAs was quantitatively described by physical models. [ABSTRACT FROM AUTHOR]