Search Results (380)

Isosymmetric phase transitions driven by subtle hydrogen-bond rearrangements remain challenging for periodic density functional theory (DFT), particularly when energy differences between polymorphs are small. Resorcinol represents an interesting case in which the α and β polymorphs crystallize in the same space group and differ primarily in hydroxyl orientation and hydrogen-bond topology. In this work, the α–β phase transition was systematically investigated using periodic DFT calculations under ambient and elevated pressure. A broad set of exchange–correlation functionals combined with different dispersion corrections was benchmarked against experimental structural and energetic data. Dispersion-corrected methods were essential for reproducing lattice parameters and the pressure-induced inversion of stability. PBESOL with Tkatchenko–Scheffler dispersion provided the most consistent agreement with the experiment and was therefore used for phonon and ab initio molecular dynamics simulations. Phonon-derived thermodynamic analysis revealed a delicate enthalpy–entropy balance governing the transition, strongly affected by pressure. Dynamical simulations confirmed the instability of the α phase under compression, demonstrating the cooperative nature of this hydrogen-bond-driven isosymmetric transformation. Full article

Atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) enables low-temperature coating in open air, yet the interplay between precursor activation and ambient-derived species remains unclear. Here, thin films from an amine precursor are deposited using a helium plasma and characterized by gas chromatography–mass spectrometry (GC-MS), a quartz crystal microbalance (QCM), and X-ray photoelectron spectroscopy (XPS). GC-MS indicates partial precursor conversion and formation of oxygen- and nitrogen-containing products, consistent with participation of ambient air and moisture. QCM identifies a limited precursor-concentration window in which mass increases monotonically during plasma exposure and remains constant after shutdown; outside this window, post-discharge mass loss occurs, indicating desorption of weakly bound species. XPS confirms carbon-rich films incorporating oxygen- and nitrogen-containing functionalities and complete substrate coverage at higher precursor concentrations. Full article

The manipulation of the electrocatalyst nanoarchitecture, particularly transition metal compounds, regarding size, shape, facets, and composition, significantly enhances the electrocatalytic activity in energy transformations. This study introduces a novel methodology for the precipitation of mesoporous nanoparticles of nickel tungstate (meso-NiWO₄) using direct chemical deposition from a template of Brij^®78 surfactant liquid crystal. Physicochemical analyses revealed the formation of amorphous meso-NiWO₄ nanoparticles with dual sizes of 10 ± 3 and 120 ± 8 nm and a specific surface area of 34.2 m²/g, exceeding that of nickel tungstate deposited in the absence of surfactant (bare-NiWO₄, 4.0 m²/g). The meso-NiWO₄ nanoparticles exhibit improved electrocatalytic stability, reduced charge-transfer resistance (R_ct = 1.11 ohm), and a current mass activity of ~365 mA/cm² mg at 1.6 V vs. RHE during the electrolysis of urea in alkaline solution. Furthermore, by employing meso-NiWO₄ in a two-electrode urea electrolyzer, a remarkable 4.8-fold increase in the cathodic hydrogen concurrent production rate was achieved (373.40 µmol/h at a bias potential of 2.0 V), compared to that of the bare-NiWO₄ catalyst. The exceptional urea oxidation electroactivity and the enhanced hydrogen evolution rate arise from substantial specific surface area and mesoporous structure, facilitating effective charge transfer and mass transport through the meso-NiWO₄ catalyst. Using the surfactant liquid crystal template for electrocatalyst synthesis enables a one-pot deposition of diverse nanoarchitectures and compositions with high surface area at ambient conditions for an improved electrocatalytic and hydrogen green production process. Full article

Self-sustained oscillatory systems enable autonomous motion through continuous interaction with ambient energy sources, positioning them as promising candidates for soft robotic actuation, energy conversion, and biomedical applications. However, their utility is often limited by inherent vibrations and frictional losses, which can lead to impaired efficiency and generate noise. To overcome these limitations, a continuously rotating disc mechanism is proposed, which exploits the photothermal response of liquid crystal elastomers (LCEs) under uniform illumination. The resulting temperature field within the material is obtained via photothermal modeling of the LCE. The rotational actuation torque is generated through mass displacement resulting from light-induced LCE contraction. Based on the above conditions, we establish the equilibrium conditions and critical thresholds for continuous motion and reveal a synergy between the thermal field and torque. Through the interplay of the temperature field and the actuating rotating moment, the system ultimately attains steady self-rotation. Therefore, the absorbed energy offsets damping losses. Numerical simulations reveal that the steady-state self-spinning and translational velocity are influenced by multiple parameters including incident heat flux, gravitational field strength, material contraction coefficient, LCE element dimensions, illumination geometry, and resistive torque. The proposed LCE disc configuration exhibits exceptional operational stability and minimal damping, which has potential for implementation in advanced soft robotic systems and mechanical energy conversion applications. Full article

This study investigates the influence of cooling rates on the structural evolution and mechanical properties of ultra-high-molecular-weight polyethylene/high-density polyethylene fibers by systematically varying cooling media from ambient air (f1) to room-temperature water (f5). A significant structural inversion was observed between the as-spun and drawn fiber stages: while slow cooling (f1) promotes thermodynamic crystallization to form large, stable grains and maximum initial crystallinity (54%), rapid quenching (f5) effectively “freezes” the molecular chains in a low-crystallinity, highly orientable precursor state by suppressing thermal relaxation. During subsequent hot-drawing, the quenched samples (f5) exhibited a superior response to tensile stress, achieving the highest maximum draw ratio due to reduced crystalline obstacles and enhanced chain mobility. This enables efficient stress-induced crystallization, leading to near-perfect crystal orientation (f_c > 0.95) and a dense microfibrillar framework. Consequently, the fiber performance trends reversed, with f5 achieving peak tensile strength (1.33 GPa) and modulus, whereas f1 remained limited by its rigid thermal history. These findings highlight that rapid quenching is essential for developing high-performance fibers by preserving a precursor structure that maximizes the potential of stress-induced crystallization. Full article

The poor stability of CsPbBr₃ perovskite nanocrystals (PNCs) caused by weak and dynamic ligand coordination severely limits their commercial applications. Herein, a dual-ligand synergistic modification strategy based on bromocarboxylic acids (BCAs) and oleylamine (OAm) was developed to mediate the surface structures and luminescent dynamics of CsPbBr₃ PNCs. The results reveal that carboxylate groups of BCA ligands modulate crystal growth, while its terminal Br atom forms a strong coordination with exposed Pb²⁺ on the PNCs surface, which can effectively passivate lead- and bromine-related defects. The synergistic protection of OAm ligands enhances the stability of PNCs via amino-halide electrostatic interactions and steric hindrance effects. Notably, based on the relatively dense surface coating of 4-bromobutyric acid (BBA) and OAm dual-ligands, the prepared CsPbBr₃ PNCs exhibit a high photoluminescence quantum yield (PLQY) of 85.2 ± 2.4% and remarkable storage stability, retaining 90.2 ± 1.7% of their initial PL intensity after being stored for 63 days under ambient conditions. Furthermore, a prototype white light-emitting diode (WLED) fabricated with these PNCs displays a wide color gamut covering 122.1% of the NTSC standard and a luminous efficacy of 64.6 lm/W. This work provides a facile and feasible ligand engineering strategy to obtain highly stable and emissive PNCs. Full article

The solid-state synthesis of alkali–tantalum(V) oxyfluorides KTa₂O₅F and CsTa₂O₅F was revisited with the aim of streamlining their preparation as single-phase polycrystalline solids. Alkali fluorides (KF, CsF) and trifluoroacetates (KH(CF₃COO)₂, CsH(CF₃COO)₂) and tantalum oxide (Ta₂O₅) were used as precursors. Reaction temperatures were optimized by means of thermal analysis coupled with powder X-ray diffraction. Phase-pure KTa₂O₅F was obtained by heating stoichiometric mixtures of KF + Ta₂O₅ and KH(CF₃COO)₂ + Ta₂O₅ at 900–1000 °C in alumina crucibles under ambient atmosphere. Similar conditions were employed to synthesize phase-pure CsTa₂O₅F from a stoichiometric mixture of CsF + Ta₂O₅ heated to 800 °C. On the other hand, the preparation of CsTa₂O₅F from a mixture of CsH(CF₃COO)₂ + Ta₂O₅ required an excess of the trifluoroacetate precursor to obtain the targeted oxyfluoride as the sole crystalline phase. Results presented herein demonstrate that mixed-metal oxyfluorides previously thought to be synthetically challenging may be synthesized via facile solid-state reactions without the need for specialized containers and stringent conditions. In addition to streamlined synthetic routes to alkali– tantalum(V) oxyfluorides, a neutron powder diffraction study of the crystal structure of KTa₂O₅F is presented to fill a gap in crystallographic databases commonly accessed by materials and solid-state chemists. Full article

Wide-bandgap diamond photodetectors face a fundamental trade-off between dark current suppression and photocurrent collection due to high Schottky barriers. Here, a photo-modulation strategy is demonstrated by integrating monolayer graphene as transparent electrodes on oxygen-terminated single-crystal diamond. The atomically thin graphene (87.3% UV transmittance at 220 nm) allows photons to penetrate and dynamically reduce Schottky barriers through photoinduced electric fields, while maintaining high barriers (~2.3 eV) under dark conditions for ultralow leakage current. Compared with conventional 100 nm Au electrodes, graphene-based devices exhibit a 4.9-fold responsivity improvement (0.158 A/W at 220 nm) and a 5.2-fold detectivity increase (8.35 × 10¹³ cm·Hz^1/2/W), while preserving ultralow dark current (~10⁻¹² A at ±100 V). XPS measurements confirm a minimal Fermi level shift (0.06 eV) upon graphene integration, demonstrating robust surface state pinning by oxygen termination. Transient photoresponse reveals a 27% faster rise time (30 ns vs. 41 ns) with bi-exponential decay governed by band-to-band recombination (τ1 ≈ 75 ns) and trap-assisted recombination (τ2 ≈ 411 ns). The devices maintain stable performance after one month of ambient exposure and successfully demonstrate UV optical communication capability. This transparent electrode approach offers a versatile strategy for enhancing wide-bandgap semiconductor photodetectors for secure communications, environmental monitoring, and industrial sensing applications. Full article

This work reports on novel acid–base conjugate pairs of monocationic allyldiamidinium and dicationic diamidinium salts, some of which are ionic liquids (ILs) at ambient temperatures. A series of allyldiamidinium salts of the general formula [C₃H(NRMe)₄]X (R = Me, Et, Pr, allyl, CH₂CH₂OMe; X = Cl, bistriflimide, dicyanamide) were prepared from C₃Cl₄ or C₃Cl₅H and the appropriate secondary amine, RNMeH. Alkylated ethylenediamines similarly yield bicyclic allyldiamidinium salts, whereas longer diamines (H₂N(CH₂)_nNH₂ (n = 3, 4, 5)) were isolated as their conjugate acids, the diamidinium dicationic salts [C₃H₂(HN(CH₂)_nNH)₂]X₂. The salts were characterized by NMR, ES-MS, DSC, TGA, and miscibility or solubility studies. Additionally, the ILs were characterized by their viscosities. The conductivities of the diamidinium ILs were also measured, and this allowed for an investigation of their Walden parameters. In contrast to expectations, since the ion pairing and clustering were expected to be significant, this showed them to be “superionic”. Previous reports of Walden plots of dicationic ILs were found to be erroneous, and a reanalysis of the literature data found that all reported dicationic and even tetracationic ILs can be classified as superionic. The salts [C₃H(NMe₂)₄]Cl, [C₃H(EtN(CH₂)₂NEt)₂]OTf, and [C₃H₂(HN(CH₂)_nNH)₂]Cl₂ (n = 3, 4, 5) were also characterized by single-crystal X-ray diffraction. Full article

We review bulk transition-metal nitrides synthesized at high pressure–high temperature and recoverable at ambient conditions. We establish an elasticity-anchored framework that links crystal structure and bonding to elastic descriptors and hardness at the phase-resolved level, enabling fair cross-study comparison. Overall, hardness shows a robust association with the shear modulus G, while the Pugh ratio k = G/B modulates relative rankings across phases. When metallic bonding or non-stoichiometry/defects are pronounced, systematic deviations arise; accordingly, elasticity-based models are best used for cross-phase trends and qualitative guidance rather than absolute predictions, especially for metallic or defect-rich phases. Building on this baseline, we outline application pathways and future research directions, and we propose a minimal reporting checklist to improve reproducibility and cross-study comparability. Full article

This study presents a comprehensive investigation of the high-pressure behavior of barium azide Ba(N₃)₂ through synchrotron X-ray diffraction, revealing critical insights into its anisotropic compressibility and phase transitions under pressures up to 28 GPa. At ambient conditions, Ba(N₃)₂ crystallizes in a monoclinic structure (space group P2₁/m), exhibiting pronounced anisotropic compression with axial compressibility following the order b > a > c. The distinct compressibility arises from the arrangement of azide ions, where interlayer interactions along the b-axis dominate the response to pressure. A reversible phase transition (Phase I → Phase II) initiates at 2.6 GPa, characterized by a monoclinic-to-monoclinic transformation involving subtle symmetry changes driven by azide ion rotation and lattice plane slippage. Above 11.8 GPa, emergent diffraction peaks suggest a potential secondary transition, though the structure remains stable up to 28 GPa. These findings underscore the unique role of azide ion dynamics in governing structural stability and phase evolution in divalent azides, offering implications for their utility as precursors in polymeric nitrogen synthesis. Full article

Self-oscillations convert ambient energy into continuous periodic motion through feedback mechanisms, but their response to external periodic disturbances is not yet fully understood. Through the combination of a photothermally-responsive liquid crystal elastomer fiber and a mass block within a linear light field, we consider a liquid crystal elastomer self-oscillator. Following theoretical modeling of the light-driven self-oscillator under external periodic forcing and numerical simulations, three distinct phase-locking regimes are identified: in-phase, anti-phase, and quadrature synchronizations. Mechanisms are elucidated through time-domain, frequency-domain, and phase-space analyses. Moreover, approximate analytical expressions for the steady-state amplitude–frequency and phase–frequency responses of the self-oscillator under periodic forcing are derived using the multi-scale method. The impact of periodic forcing on the self-oscillator and its response regulation via system parameters is examined. A close correspondence exists between numerical and analytical results. This work investigates the response characteristics of a liquid crystal elastomer self-oscillator under periodic forcing, advances fundamental insights into disturbance rejection in self-oscillators, and delivers practical guidance for their robust operation in complex oscillatory settings. Full article

Background: Clonazepam is a benzodiazepine drug indicated in all clinical forms of epileptic seizures, various forms of myoclonic seizures, myoclonus and other abnormal movements. At present, it is classified as a hazardous drug requiring special precautions for personnel at reproductive risk, according to a technical document produced by the Spanish National Institute for Safety and Health at Work (INSST), in collaboration with the Spanish Society of Hospital Pharmacy (SEFH). The commercial solutions of clonazepam, for oral and parenteral administration, are supplied by laboratories in glass containers. Repacking in pre-filled polypropylene (PP) syringes, made in the pharmacy service, and in aseptic conditions, may facilitate its administration and reduce the risks to the health or safety of nursing personnel. Nevertheless, there is a lack of stability studies of clonazepam in pre-filled PP syringes. Objectives: To evaluate the physicochemical stability of commercial clonazepam 2.5 mg/mL oral solution and 1 mg/mL parenteral solution repackaged in pre-filled PP syringes under various storage conditions. Methods: A rapid, linear, precise and sensitive high-performance liquid chromatography (HPLC) method for chemical stability studies of Clonazepam 1 mg/mL (parenteral use) and 2.5 mg/mL (oral use) in solution was implemented after repackaging in pre-filled PP syringes. The studies were conducted by measuring concentrations of oral and parenteral clonazepam in pre-filled syringes, at various time points, over 30 days in several different storage conditions: oral clonazepam protected from light in refrigerator and at controlled room temperature exposed to ambient light; parenteral clonazepam protected from light in a refrigerator and at controlled room temperature protected or unprotected from light. Visual aspects and pH change as well as crystal formation were checked to determine physical stability. Results: The degradation of the active ingredient in all groups was less than 10% after 30 days. No evidence of crystal formation, pH and visual aspect changes were observed. Conclusions: Clonazepam 1 mg/mL parenteral solution and 2.5 mg/mL oral solution in pre-filled PP syringes are stable for up to 30 days in the tested conditions. The centralized repackaging of clonazepam in pre-filled PP syringes, connected to a closed safety system, in the pharmacy service, reduces drug manipulation by nursing staff decreasing the risk of occupational exposure. Full article

Pazufloxacin is a fluoroquinolone antibiotic synthesized by Toyama Chemical Co., Ltd. (Tokyo, Japan) in the 1990s. Up until now, the X-ray crystal structure of its mesylate salt had not been determined. The dissolution and recrystallization of pazufloxacin mesylate from different solvents afforded the salts pazufloxacinium mesylate (1), pazufloxacinium mesylate dihydrate (2), pazufloxacinium mesylate hydrate (3) and pazufloxacinium mesylate bis(peroxosolvate) (4), which were all crystallographically characterized. Molecular and crystal structures of these compounds, as well as their thermal behavior, were studied. For all compounds, single-crystal X-ray diffraction confirmed that a proton migrates from methanesulfonic acid to the amino group of pazufloxacin to form a salt. Dehydration of two hydrates occurs as a two-step single-crystal-to-powder process, leading to the formation of two metastable polymorphs of the anhydrous salt. In the solid state, the peroxosolvate compound is stable under ambient conditions for several months, thus making this drug–drug solid suitable for topical application. Full article

Organic phase change materials (OPCMs) offer high energy density for thermal storage but suffer from crystallization kinetics dependent on ambient temperature, leading to uncontrolled heat release and limited storage lifetime. Although doping OPCMs with azobenzene (Azo) derivatives enables optically controlled energy storage and release, existing systems require UV irradiation for E-to-Z isomerization. This UV dependency seriously hinders their development in practical solar applications. Herein, we develop a visible-light-responsive Azo@OPCM composite by doping tetra-ortho-fluorinated azobenzene into eicosane. Systematic characterization of composites with different dopant ratios via UV–visible spectroscopy and differential scanning calorimetry reveals that green-light irradiation drives E-to-Z isomerization, achieving 97–99% Z-isomer conversion. This photoisomerization could introduce supercooling through photo-responsive energy barriers generated by Z-isomer, allowing thermal energy storage at lower temperatures. Subsequent blue-light irradiation triggers Z-to-E reversion to eliminate supercooling and enable optically controlled heat release. Additionally, by regulating the molar ratios of dopant, the optimized composites achieved 280.76 J/g energy density at 20% molar doping ratio, which surpassed that of pure eicosane and the reported Azo-based photothermal energy storage system. This work establishes a complete visible-light-controlled energy harvesting–storage–release cycle with significant potential for near-room-temperature solar thermal storage applications. Full article