Low Melting Point Research Articles

Ultra-rapid Synthesis of High-entropy MAX Phases and Their Derivative MXenes for Battery Electrodes.

High-entropy materials hold immense promise for energy storage, owing to their varied compositions and unforeseen physicochemical properties, yet, which poses challenges in synthesis due to tendentious phase separation and extended sintering durations. Herein, an ultra-rapid strategy based on spark plasma sintering (SPS) techniques is proposed to synthesize high-entropy MAX phases within 15 minutes, including a new phase of (Ti0.2V0.2Cr0.2Nb0.2Mo0.2)4AlC3 and several phases of 413-type TiVNbMoAlC3, TiVCrMoAlC3 and (Ti0.2V0.2Cr0.2Nb0.2Ta0.2)4AlC3, achieving utmost purity level up to 99.54%. Under high temperature, the overfeed of Al with low melt point (~660°C) can foster a liquid environment, which remits the immiscibility among starting materials and benefits to diffusion dynamics to some extents. Theoretical calculations are employed to elucidate the thermodynamic preponderance of high-entropy MAX phases in the intricate multi-element systems. Meanwhile, the varied stacking modes among MX slabs in high-entropy MAX phases and the distinct topological transformations to their derivative MXenes can be observed directly at the atomic level. Moreover, four high-entropy MXenes as electrode materials were investigated for rechargeable batteries. Among them, TiVNbMoC3 electrode demonstrates superior lithium-ion storage capabilities with 725 mAh g-1 after 1000 cycles at 1 A g-1, triggering the edification to the application of high-entropy MXenes for energy domain.

Modification of Glucose Metabolic Pathway to Enhance Polyhydroxyalkanoate Synthesis in Pseudomonas putida

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are semi-crystalline elastomers with a low melting point and high elongation at break, allowing for a wide range of applications in domestic, agricultural, industrial, and mainly medical fields. Utilizing low-cost cellulose hydrolyzed sugar as a carbon source and metabolic engineering to enhance synthesis in Pseudomonas putida is a promising strategy for commercializing mcl-PHAs, but little has been attempted to improve the utilization of glucose for synthesizing mcl-PHAs. In this study, a multi-pathway modification was performed to improve the utilization of substrate glucose and the synthesis capacity of PHAs. To enhance glucose metabolism to flow to acetyl-CoA, which is an important precursor of mcl-PHA, multiple genes in glucose metabolism were inactive (branch pathway and negative regulatory) and overexpressed (positive regulatory) in this study. The two genes, gcd (encoding glucose dehydrogenase) and gltA (encoding citrate synthase), involved in glucose peripheral pathways and TCA cycles were separately and jointly knocked out in Pseudomonas putida QSRZ6 (ΔphaZΔhsdR), and the mcl-PHA synthesis was improved in the mutants; particularly, the mcl-PHA titer of QSRZ603 (ΔgcdΔgltA) was increased by 33.7%. Based on the glucose branch pathway truncation, mcl-PHA synthesis was further improved with hexR-inactivation (encoding a negative regulator in glucose metabolism). Compared with QSRZ603 and QSRZ6, the mcl-PHA titer of QSRZ607 (ΔgcdΔgltAΔhexR) was increased by 62.8% and 117.5%, respectively. The mutant QSRZ609 was constructed by replacing the endogenous promoter of gltB encoding a transcriptional activator of the two-component regulatory system GltR/GltS with the ribosome subunit promoter P33. The final mcl-PHA content and titers of QSRZ609 reached 57.3 wt% and 2.5 g/L, an increase of and 20.9% and 27.3% over that of the parent strain QSRZ605 and an increase of 110.4% and 159.9% higher as compared to QSRZ6, respectively. The fermentation was optimized with a feeding medium in shaker flacks; then, the mcl-PHA contents and titer of QSRZ609 were 59.1 wt% and 6.8 g/L, respectively. The results suggest that the regulation from glucose to acetyl-CoA by polygenic modification is an effective strategy for enhancing mcl-PHA synthesis, and the mutants obtained in this study can be used as chassis to further increase mcl-PHA production.

Ultra‐rapid Synthesis of High‐entropy MAX Phases and Their Derivative MXenes for Battery Electrodes

High‐entropy materials hold immense promise for energy storage, owing to their varied compositions and unforeseen physicochemical properties, yet, which poses challenges in synthesis due to tendentious phase separation and extended sintering durations. Herein, an ultra‐rapid strategy based on spark plasma sintering (SPS) techniques is proposed to synthesize high‐entropy MAX phases within 15 minutes, including a new phase of (Ti0.2V0.2Cr0.2Nb0.2Mo0.2)4AlC3 and several phases of 413‐type TiVNbMoAlC3, TiVCrMoAlC3 and (Ti0.2V0.2Cr0.2Nb0.2Ta0.2)4AlC3, achieving utmost purity level up to 99.54%. Under high temperature, the overfeed of Al with low melt point (~660°C) can foster a liquid environment, which remits the immiscibility among starting materials and benefits to diffusion dynamics to some extents. Theoretical calculations are employed to elucidate the thermodynamic preponderance of high‐entropy MAX phases in the intricate multi‐element systems. Meanwhile, the varied stacking modes among MX slabs in high‐entropy MAX phases and the distinct topological transformations to their derivative MXenes can be observed directly at the atomic level. Moreover, four high‐entropy MXenes as electrode materials were investigated for rechargeable batteries. Among them, TiVNbMoC3 electrode demonstrates superior lithium‐ion storage capabilities with 725 mAh g−1 after 1000 cycles at 1 A g‐1, triggering the edification to the application of high‐entropy MXenes for energy domain.

Simultaneous fluoridation strategies for achieving high thermionic emission and low melting point in aluminate impregnants for Ba-W cathodes

Simultaneous fluoridation strategies for achieving high thermionic emission and low melting point in aluminate impregnants for Ba-W cathodes

In situ iron coating of amorphous boron and characterization of its energy release behavior

Boron was widely employed as metal fuel in solid propellants for its higher gravimetric and volumetric combustion enthalpies. However, the low melting point and high boiling point of B2O3 on the surface of boron particles significantly hinder its ignition and combustion performance, seriously preventing the full realization of its thermodynamic potential. To address this issue, B@Fe composite fuels with different iron contents from 1.59 % to 7.09 % were prepared via liquid phase reduction in this paper and the quasi-static high temperature oxidation, ignition and combustion reaction characteristics and corresponding mechanism were studied, in order to provide effective modification techniques in supporting the large-scale engineering application of boron as metal fuel. The study results show that B@Fe can effectively reduce the ignition temperature and maximum heat flow temperature of amorphous boron, and increase the maximum mass gain rate. The ignition temperature and maximum heat flow temperature have an exponential function with the iron coating content. Iron coated amorphous boron can effectively shorten the laser ignition delay time by more than 50 %, and significantly change the flame structure, flame evolution process and combustion duration. Both amorphous boron and iron-coated amorphous boron flame showed a multi-layer structure, including the outer green flame, the middle yellow flame and the central incandescent flame. However, with the increase of the iron coating content, the flame height increased from 5.5 cm to 6.3 cm, the flame structure changed from mushroom type to triangle type, and the central incandescent flame area increased significantly. The equivalent combustion duration increased from 975 ms to 1997 ms, and the flame temperature increased from 1288 to 1505 °C. The emission spectra of BO2 and BO lines are captured during combustion. B@Fe with the increase of iron content, a large number of small diameter micropores appear in the condensed combustion products(CCPs) of composite fuels, and a grid-like structure was formed. With the increase of iron coating content, the boron content of condensed combustion products decreases, and the oxygen content increases. The main components of CCP include B, B2O3, B6O, FeB, Fe2B and Fe3B. Based on the ignition combustion experiment of B@Fe composite fuel, ignition combustion analysis model of B@Fe composite fuel was established.

Multiple effects of high efficiency solid inertants on fire hazard of the accumulated Mg dust layer

Due to low melting and boiling points and extreme reactivity in the chemical reaction of Mg powder, inert powders that have a significant inerting effect on Mg dust clouds can cause significant combustion enhancement of the accumulated Mg dust layer. To circumvent this unforeseen fire hazard, this research selects five types of inertants that have been demonstrated to exert an inerting effect on metal dust clouds and possess a potential flame-retardant effect on Mg dust layers. This research aims to investigate the effect of inert powders on Mg dust layers to identify an efficient inerting mechanism for Mg dust layers. The results indicate that the selection of inertants for Mg dust must be based on a comprehensive evaluation of their physical and chemical properties. The presence of substances with strong decomposition and decomposition products that readily produce gases will destroy the oxide crust on the surface of the accumulated Mg dust layer, thereby causing violent gas-phase combustion. In the case of highly chemically stable substances, the melting point is of primary importance. The formation of cracks in the oxide crust is also a consequence of the higher melting point of inertants, resulting in a combustion enhancement of the mixed dust layer. Inertants with a low melting point and a high boiling point demonstrate a high degree of inerting efficiency for Mg dust layers. The melting of the inert substances forms a liquid film, which prevents the Mg powder from coming into contact with the air surrounding and within the combustion zone. The results of this research are both instructive and valuable for preventing explosions in the process industry involving metal dust materials.

Outer Helmholtz plane adsorption regulation to achieve low-concentration of pure propylene carbonate solvent electrolytes compatible with graphite anode

The low melting point and high polarity of propylene carbonate (PC) make it an ideal solvent for electrolytes of lithium-ion batteries (LIBs), but the incompatibility with graphite anode hinders the application. In the present study, a new method is developed to solve this problem from a new viewpoint. Introduction of saturated LiNO3 (0.14 mol L‒1) into pure PC electrolyte containing lithium salt with normal concentration (1.38 mol L‒1) leads to a perfect compatibility with graphite anode. Li/Graphite cell using this pure PC electrolyte shows a reversible capacity of 350.0 mAh g‒1 and a 200-cycle capacity retention of 96.3 %. Further mechanism study and theoretical computation indicate that the NO3‒ anions are adsorbed to outer Helmholtz plane of the electric double layer at the graphite anode interface. This changes the Li+ solvation structure in the electric double layer, facilitating the Li+ desolvation process hence resulting in high compatibility with the graphite anode. The most prominent advantage of the present strategy is that, because of the adsorption of NO3‒ anions to the outer Helmholtz plane, the compatibility with graphite anode could be improved by introduction of tiny amount of Li salt without large change of the bulk phase properties of the electrolyte. This work provides a new understanding of the compatibility from the viewpoint of outer Helmholtz plane, which might deliver new insights for the optimization of electrolytes for LIBs.

Retinol-Loaded Deep Eutectic Solvent emulsion: Improved Stability and Therapeutic Efficiency

Retinol is used to manage epidermal and keratin metabolism, promote collagen formation, erase wrinkles for firmer skin, and restore suppleness and smoothness. Retinol can be difficult to store and use owing to the potential for skin irritation, oxidation, and biological ineffectiveness. The linolenic acid and phosphatidylcholine deep eutectic solvent (DES) had a low melting point, high bioactivity, and integrated capsule technology for retinol encapsulation. Safety evaluation tests revealed that the formulated DES-retinol emulsion was less cytotoxic than free retinol, as well as less irritant toward chicken embryos, pig skin, and human patches. In a keratinocyte inflammatory factor inhibition assay, the DES-retinol emulsion reduced monocyte chemoattractant protein-1 expression, indicating the potential to reduce the inflammatory response of the skin to retinol-induced irritation. The DES-retinol emulsion exhibited pro-permeability, anti-wrinkle, firming, and antioxidant characteristics in cellular, skin, and clinical investigations. The DES-retinol emulsion promoted type I collagen production, suppressed matrix metalloproteinase-1 activity, and reduced the release of reactive oxygen species. Consequently, the quantity, size, and depth of wrinkles were substantially improved, along with an enhanced anti-aging effect, heightened skin hydration, increased collagen intensity and flexibility, and diminished retinol-induced irritation. In conclusion, the retinol-loaded linolenic acid and phosphatidylcholine DES emulsion exhibited improved stability, enhanced transdermal efficiency, and notable therapeutic effects.

Effect of Source-Sink Misalignment and Sink Cavity Aspect Ratio on the Thermal Performance of Gallium Heat Sinks

Herein, we numerically investigated methods to improve heat dissipation from the base of a phase-change material (PCM) heat sink exposed to high heat flux (15 W/cm2). The sink cavity exhibited a rectangular cross-section with two opposite vertical walls of high thermal conductivity. These walls serve as heat-dissipating fins. We used gallium, a metallic PCM with high thermal conductivity and a low melting point to improve heat dissipation by leveraging buoyancy-driven circulations within the molten gallium. We adopted a method to position the sink base on top of the heat source surface in such a way to augment temperature gradients within the liquid to induce imbalances in gallium density and consequent internal circulations. In this technique, one vertical wall is subjected to forced-convective heat exchange with the surroundings, while the other remains adiabatic. Subsequently, for the case which showed optimum performance, we relaxed the adiabatic thermal boundary condition applied at one of the vertical walls and replaced it with convective heat transfer condition, and assessed the sink performance based on that. Further, we analyzed the impact of various aspect ratios of the sink cavity on the induced internal circulations and base cooling. Sink cavities with aspect ratios of 1.33, 0.96, and 0.64 corresponding to sink heights of 20, 17, and 14 mm, respectively, were examined under a consistent heat flux applied across a 15-mm base length. We also investigated the precise positioning of the sink base relative to the heat source surface and explored its influence on temperature gradients and gallium density imbalances crucial for induced internal circulations. Results indicate that a sink cavity aspect ratio of 0.96 yields the optimal heat dissipation from the base. Further, aligning the left bottom edge of the sink base with the left edge of the heat source surface maximizes heat dissipation to the ambient surroundings, thereby prolonging latent-heat dumping into the sink before the gallium completely melts. Any misalignment between the sink base and the surface of the heat source may have a profound impact on the temporal evolution of induced internal circulations within the molten gallium, essentially affecting heat dissipation from the sink base.

Boosting Enzyme Activity in an Anhydrous Gas Flux with Amphiphilic Polymers

AbstractGas‐phase enzymatic catalysis offers great potential for both green synthesis and the efficient degradation of volatile chemicals. However, solid enzymes often exhibit extremely low activity compared to their counterparts in native aqueous phase. Although a few immobilization methods have succeeded in increasing activity by preserving enzyme structure, approaches for boosting enzyme activity remain underdeveloped. In this study, we propose a general and facile method to boost enzyme activity in the gas phase, which utilizes amphiphilic polymers to energize enzyme conformational dynamics and thus enhance enzyme catalysis kinetics. The triblock copolymer Pluronics with low melting points were co‐lyophilized with Candida antarctica lipase B (CalB), yielding Pluronic/CalB powders that appeared a 70‐fold increase in activity compared to free CalB powder. Low‐field nuclear magnetic resonance (LF‐NMR), solid‐state nuclear magnetic resonance (ssNMR) and dielectric relaxation spectroscopy identified the enhancement of enzyme dynamics on the µs–ms timescale, whereas Fourier transform infrared spectroscopy (FTIR) detected structural perturbations of the native enzyme in Pluronic/CalB. The apparent activity of the enzyme/polymer powders correlated positively with both enzyme dynamics and polymer flexibility. These findings provide new molecular physical insights into gas‐phase enzyme catalysis, which are essential for advancing enzyme applications in nonnatural scenario.

Anion‐repulsive polyoxometalate@MOF‐modified separators for dendrite‐free and high‐rate lithium batteries

AbstractCommercial polyolefin separators in lithium batteries encounter issues of uncontrolled lithium‐dendrite growth and safety incidents due to their low Li+ transference numbers () and low melting points. To address these challenges, this study proposes an innovative approach by upgrading conventional separators through the incorporation of metal‐organic framework (MOF)‐confined polyoxometalate (POM). The presence of POM restricts anion diffusion through electrostatic repulsion while facilitating Li+ transport within MOF nanochannels through their affinity for lithium ions. Moreover, MOF confinement effectively mitigates the acidification of electrolytes induced by POM. As a proof‐of‐concept, the polypropylene separators decorated with phosphotungstic acid@UIO66 (denoted as PW12@UIO66‐PP) exhibit remarkable lithium‐ion conductivity of 0.78 mS cm−1 with a high of 0.75 at room temperature. The modified separators also display excellent thermal stability, preventing significant shrinkage even at 150°C. Furthermore, Li symmetric cells employing PW12@UIO66‐PP separators exhibit stable cycling for 1000 h, benefiting from rapid Li‐ion transport and uniform deposition. Additionally, the modified separator shows promising adaptability to industrial manufacturing of lithium‐ion batteries, as evidenced by the assembly of a 4 Ah NCM811/graphite pouch cell that retains 97% capacity after 350 cycles at C/3, thus highlighting its potential for practical applications.

Hot deformation behavior of an ignition resistance Mg–6Zn-0.6Zr-1.2Ca magnesium alloy

The addition of Ca could enhance the ignition point of magnesium alloys but impairing their workability, so it is essential to study the hot deformation behavior of new Ca-containing ignition resistance magnesium alloys. The hot deformation behavior of a new ignition resistance Mg–6Zn-0.6Zr-1.2Ca alloy was investigated by compression experiment in the temperature range of 240 °C–360 °C, strain rates of 10−3 s−1-1 s−1 and height reduction of 10%–60%. The true stress-strain curves show that flow stress decreases as the deformation temperature increases or the strain rate decreases. Microstructure analysis shows that higher temperatures and lower strain rates are favorable for DRX, while higher strain rates promote the fragmentation of the Ca2Mg6Zn3 phase. Meanwhile, the existence of Ca2Mg6Zn3 phase make the DRX process be dominated by the particle-induced subgrain nucleation mechanism. By superposition of the power dissipation map and the instability map, a hot processing map of true strain of 0.6 is generated. According to analyses on the processing map and microstructure evolution, the instability of processing map can be attributed to the greater dislocation motion resistances, insufficient DRX, and Ca2Mg6Zn3 phase with low-melting point. Conversely, the optimal processing parameters for the alloy were determined as 280–360 °C/0.001–0.01 s−1 in safe zone with a high η above 0.3, which can be due to the apparent DRX and good deformation coordination.

Examining the Influence of Silver(I) Ion Coordination Environment in Ionic Liquids on Olefin-Paraffin Separations using Inverse Gas Chromatography.

Silver(I) ions (Ag+) undergo selective π-complexation with olefins and have been employed as separation media for the isolation of olefins from structurally similar paraffins. Ionic liquids (ILs) possess minimal vapor pressures, exceptional thermal stabilities, low melting points, as well as provide a favorable environment for π-complexation between Ag+ ions and olefins. The development of molecular drivers capable of highly selective olefin/paraffin separation systems with Ag+-containing ILs necessitates a comprehensive understanding of all factors that affect olefin solubility and selectivity. This study examines how coordinating different ligand species to Ag+ ions produces separation media with varying interaction strengths to olefins. Four coordination compounds, (4,4'-dimethyl-2,2'-bipyridine)silver(I) bis[(trifluoromethyl)sulfonyl]imide ([Ag+(DMBP)][NTf2-]), bis(pyridine)silver(I) [NTf2-] ([Ag+(Py)2][NTf2-]), bis(2,6-lutidine)silver(I) [NTf2-] ([Ag+(Lut)2][NTf2-]), and (triphenylphosphine)silver(I) [NTf2-] ([Ag+(PPh3)][NTf2-]) were dissolved in the 1-decyl-3-methylimidazolium [NTf2-] ([DMIM+][NTf2-]) IL and employed as stationary phases for inverse gas chromatography. Ligand coordination to the Ag+ ion was observed to modulate interactions of unsaturated hydrocarbons. The [Ag+(Py)2][NTf2-] complex offered the greatest olefin retention among the coordination complexes reaching 54% of the 1-octene retention factor of the uncoordinated [Ag+][NTf2-]. Hydrogen (H2) exposure studies showed ligand-dependent rates of reduction from Ag+ ion to elemental silver (Ag0). The [Ag+(PPh3)][NTf2-] complex exhibited superior stability, compared to the neat [Ag+][NTf2-] salt, reducing the retention factor of 1-octene by 15.3% and 19.4%, respectively, after 200 h of H2 exposure at 70 °C. The results from this study show that coordination complexes with Ag+ ions are useful in highly selective and efficient petroleum processing systems.

An experimental and comparative study on passive and active PCM cooling of a battery with/out copper mesh and investigation of PCM mixtures

The carbon emission contribution to global warming accelerated both research on and transition to electric vehicles (EVs). Drivers demand high power, fast acceleration and less charging times. All these demands require high C rate charging/discharging demands from batteries. The rate of heat generation is exponentially proportional to C rates which decreases battery lifetime and may lead to thermal runaway. However, a battery thermal management system decreases thermal runaway risk and decelerates battery degradation via controlling battery temperature. In this paper, we first document the thermal conductivity enhancement via copper foam into phase change material (PCM) domain to uncover their possible use in EV thermal management applications. Maximum 15.93 times increment is achieved with a specific copper foam. Then, physical properties and behaviors of distinct PCM mixtures are documented. Homogeneity of mixtures is associated with the chemistry of PCMs and the mixture melting point is proportional to the volume weighted average of melting temperatures. The results document that the PCM with relatively lower melting point is beneficial when end of discharge temperatures considered, except for high discharge rate of 2C. Temperature uniformity across the battery increases with relatively higher melting point PCM. Experiments also document that the amount of PCM volume lost via insertion of copper foam yields higher end of discharge temperatures. Overall, both PCM and copper foam enhances temperature homogeneity and their benefit becomes more sensible during drive cycles relative to continuous charge/discharge use cases.

Crystallization Behavior and Structure of CaO–SiO2–Al2O3 Melts Representing the Oxide Inclusions in Si‐Mn Deoxidized Steel

For further optimization of the inclusion plasticization control process of Si‐Mn deoxidized steel, the crystallization behavior and structure of CaO–SiO2–Al2O3 system inclusions are investigated. The crystallization behavior of four typical low melting point CaO–SiO2–Al2O3 inclusions at 1000 to 1250 °C is studied by steel crucible isothermal heating experiment. The obtained results reveal that the glassy stability of the inclusions is high when the composition of low melting point inclusion is located in the eutectic region of tridymite, pseudowollastonite, and anorthite in the ternary phase diagram. However, when the composition of the inclusion is located in the eutectic region of melilite, pseudowollastonite, and anorthite, it is easy to undergo glass‐crystallization transformation and precipitate wollastonite and anorthite crystalline phases when isothermal heating at 1100 to 1200 °C. In addition, the crystallization mode of these inclusions is mainly surface crystallization, and the crystallization degree of inclusions increases with the increase of heat treatment temperature and time. The activation energy of crystallization and the content of nonbridging oxygen in the silicate structure NBO/T can be used to predict the crystallization ability of inclusions. The greater the activation energy of crystallization and the smaller the NBO/T value, the higher the glassy stability of the inclusions.

Molecular dynamics simulations of uranyl and plutonyl cations in a task-specific ionic liquid.

Ionic liquids (ILs) are a unique class of solvents with potential applications in advanced separation technologies relevant to the nuclear industry. ILs are salts with low melting points and a wide range of tunable physical properties, such as viscosity, hydrophobiciy, conductivity, and liquidus range. ILs have negligible vapor pressure, are often non-flammable, and can have high thermal stability and a wide electrochemical window, making them attractive for use in separations processes relevant to the nuclear industry. Metal salts generally have a low solubility in ILs; however, by incorporating new functional groups into the IL cation or anion that promote complexation with the metal, the solubility can be greatly increased. One such task-specific ionic liquid (TSIL) is 1-carboxy-N, N, N-trimethylglycine bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) [Nockemann et al., J. Phys. Chem. B 110, 20978-20992 (2006)]. Water, which is detrimental for electrochemical separations, is a common impurity in ILs and can coordinate with actinyl cations, particularly in ILs containing only weakly coordinating components. Understanding the behavior of actinides in TSIL/water mixtures on a molecular level is vital for designing improved separations processes. Classical molecular dynamics simulations of uranyl(VI) and plutonyl(VI) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) with deprotonated Hbet (betaine) and water have been performed to understand the coordination and dynamics of the actinyl cations. We find that betaine is a much stronger ligand than water and prefers to coordinate the metal in a bidentate manner. Potential of mean force simulations yield a relative free energy for betaine coordination of approximately -120 to -90 kJ/mol in mixtures with water. As the amount of betaine coordinated to the actinide increases, the diffusion coefficient of the actinyl cation decreases. Moreover, the betaine ligand is able to bridge between two metal centers, resulting in dimeric complexes with actinide-actinide distances of ∼5Å. Potential of mean force simulations show that these structures are stable, with relative free energies of up to -40 kJ/mol. The crystal structure for [(UO2)2(bet)6(H2O)2][Tf2N]4 shows that the betaine bridges between two uranium atoms to form dimeric complexes similar to those found in our simulations [Nockemann et al. Inorg. Chem. 49, 3351-33601 (2010)].

Highly Refractive Transparent Half‐Heuslers for Near Infrared Optics and Their Material Design

AbstractAdvanced control of light focusing, reflection, and transmission is possible with highly refractive transparent materials; however, such materials are difficult to discover because of the negative correlation between the refractive index and the optical band gap. This study elucidates half‐Heuslers as highly refractive transparent materials, considering their densely packed crystal structures comprising both covalent and ionic bonds with d orbitals. Theoretical calculations revealed that 22 ternary half‐Heusler systems (αβγ) exhibited higher refractive indices with wider band gaps than conventional high‐refractive‐index‐transparent materials in the near‐infrared region. The key to achieving a high index and wide gap is aligning α‐d and β‐d levels within a small lattice frame given by small γ elements to the verge of forming Γ‐point conduction band minimum. Experimental examinations revealed that α and γ elements with low and high melting points are preferred for the thin‐film preparation of the well‐ordered half‐Heuslers. Highly refractive transparent half‐Heuslers and their material designs expedite post‐silicon technology for controlling near‐infrared light.

Counterintuitive Isomerization of TFSI- and TFSI--Cation Correlated Isomerization: Insights into the Low Melting Points of TFSI--Based Ionic Liquids.

Ionic liquids (ILs), particularly bis(trifluoromethane)sulfonamide (TFSI-)-based ILs, have attracted substantial attention in electrochemical energy storage, ionic gating for superconductivity, and iontronic sensing. However, underestimating TFSI- isomerization and overlooking TFSI--cation correlation make the origin of their most characteristic property, low melting points (Tm), ambiguous. Traditional static electronic structure calculations assume that C2-symmetric trans enantiomers of TFSI- easily isomerize into cis enantiomers through four symmetrically equivalent pathways over a barrier of 7.1 kJ mol-1. Herein, ab initio molecular dynamics (AIMD) simulations combined with metadynamics reveal that the unusual oscillation of the central nitrogen atom promotes TFSI- to undergo complex isomerization. Specifically, asymmetric trans-to-cis diastereomers of TFSI- experience restricted interconversion (20-52 kJ mol-1) through four distinct asymmetric pathways. The adaptive oscillation and hybridization of chiral nitrogen boost nN → σ*S-C negative hyperconjugation for stabilizing conformational structures and enlarging energy barriers. The orientational distortion of oxygen atoms' lone pairs enhances conjugation but breaks the C2-symmetry. The coexistence of both helicity and chiral nitrogen breaks the enantiomeric relationship. Furthermore, Raman characterization and AIMD simulations confirm the positive correlation between the relative stability of cis-TFSI- and its countercation's polarity. TFSI- and countercations make a mutual conformational selection instead of free isomerization. Surprisingly, Tm increases with the cation-dependent conformational rigidity of TFSI-, offering new fundamental insights into the low Tm of ILs. This descriptor encoding the dependence of thermal property on cation-anion correlated isomerization provides material design guidelines and property prediction capability.

Computer-aided design of thermosetting benzoxazoles containing bis-endoalkynyl groups: Low melting points and high thermal stability

High-temperature-resistant polybenzoxazoles (PBOs) have recently become a prominent research area due to their potential applications in aviation and aerospace. However, achieving a balance between thermal stability and processability remains a significant challenge. In this study, a computer-aided method to develop PBOs with high thermal stability and processability is explored. First, thermoset benzoxazoles (CPBOs) are designed using a material genomic approach. Subsequently, their zero shear viscosity, temperature at 50 % thermal weight loss, dielectric constant and dielectric loss are predicted using a computer-aided method. Finally, two screened thermosetting benzoxazoles, CPBO-1 and CPBO-6, are synthesized and experimentally validated. The experiments indicate that their melting points are below 100 °C, with the lowest melt viscosities being 0.5 Pa•s and 1.5 Pa•s, respectively. The corresponding polymers, pCPBO-1 and pCPBO-6, feature high thermal stability. The 5 % weight loss temperature of pCPBO-1 in N2 is 618.9 °C, while the dielectric constant and dielectric loss are 3.1 and 0.0063, respectively. These are excellent values for thermosetting resins. This computer-aided screening method is more efficient and cost-effective compared to conventional trial-and-error methods.

Generation of multiply charged metal ions in a high current short pulse vacuum arc

We have studied the plasma composition of a high current short pulse vacuum arc discharge with different cathode materials: lanthanum, gadolinium, lead, silver, and tin. We find that for optimal vacuum arc discharge parameters – arc current pulse duration about 2 μs and amplitude about 3 kA – the maximum ion charge state is 11+ and mean ion charge state from 7.8+ for tin to 9.6+ for lanthanum. The mean ion charge state for different materials depends on the discharge voltage and the energy required for ionization to maximum charge state. The cathode surface heats to a temperature of 700 °C–1100 °C in the course of the arc current pulse, depending on the cathode material, and the cathode surface of low melting point metals such as lead and tin melts to a depth of 5 μm and 10 μm, respectively. Surface melting does not lead to change in plasma ion composition, since the ion flux from the cathode considerably exceeds the evaporated atom flux.