Phase Transition for Zinc Sulfide Nanosheets under High Pressure

This study describes the pressure-induced behavior of ZnS nanosheets by synchrotron angle-dispersive X-ray diffraction (ADXD) measurement up to 32.7 GPa. ZnS nanosheets transform from zinc blende structure to rock salt phase at 13.1 GPa and subsequently to a <i>Cmcm</i> structure at 20.3 GPa. The transition to the <i>Cmcm</i> structure is irreversible for ZnS nanomaterials at a much lower critical pressure than required for ZnS bulk materials. The special morphology of ZnS nanosheets plays a crucial role in the transition to <i>Cmcm</i> structures at comparatively low pressure. Continuous changes in lattice volume in the absence of volume collapse are observed after the transition from rock salt to the <i>Cmcm</i> structure occurs

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Morphology-Tuned Phase Transitions of Horseshoe Shaped BaTiO₃ Nanomaterials under High Pressure

Exploring new physical properties of nanomaterials with special morphology have been important topics in nanoscience and nanotechnology. Here we report a morphology-tuned structural phase transition under high pressure in the horseshoe shaped BaTiO₃ nanomaterials with an average diameter of 26 ± 4 nm. A direct structural phase transition from the tetragonal to the cubic phase without local rhombohedral distortion was observed at about 7.7 GPa by in situ high-pressure X-ray diffraction and Raman spectroscopy, which is clearly different from the phase transition processes of the BaTiO₃ bulks and nanoparticles. Additionally, bulk modulus of the tetragonal and cubic phases were determined to be 125.0 and 211.7 GPa, respectively, obviously smaller than the estimated values for BaTiO₃ nanoparticles with the same grain size. Further analysis shows that the unique phase transition process and the enhanced structural stability of the tetragonal horseshoe shaped BaTiO₃ nanomaterials, may be attributed to the similar axes compressibility. Comparing with the high-pressure study on BaTiO₃ nanoparticles, this study suggests that the morphology plays an important role in the pressure-induced phase transition of BaTiO₃ nanomaterials

Luminescence Properties of Compressed Tetraphenylethene: The Role of Intermolecular Interactions

Mechanochromic materials with aggregation-induced enhanced emission (AIEE) characteristic have been intensively expanded in the past few years. In general, intermolecular interactions invariably alter photophysical processes, while their role in the luminescence properties of these AIEE-active molecules is difficult to fully recognize because the pressurized samples possess amorphous nature in many cases. We now report the high-pressure studies on a prototype AIEE-active molecule, tetraphenylethene, using diamond anvil cell technique with associated spectroscopic measurements. An unusual pressure-dependent color, intensity, and lifetime change in tetraphenylethene has been detected by steady-state photoluminescence and time-resolved emission decay measurements. The flexible role of the aromatic C–H···π and C–H···C contacts in structural recovery, conformational modification, and emission efficiency modulation upon compression is demonstrated through structure and infrared analysis

Preparation and Performance of a P–N Containing Intumescent Flame Retardant Based on Hydrolyzed Starch

<p>Halogen-free flame retardant is receiving an increased attention recently due to its hypotoxicity and high efficiency. Intumescent flame retardant is a hot spot in research of the halogen-free flame retardant. In this work, a P–N containing intumescent flame retardant named hydrolyzed starch phosphamide from melamine was synthesized via hydrolysis of starch, phosphorylation of the starch with phosphorus oxychloride, and the reaction between the phosphorylated starch and melamine. PU/hydrolyzed starch phosphamide from melamine composites was prepared using different additive amounts of hydrolyzed starch phosphamide from melamine. Fourier transform infrared, scanning electron microscopy, and thermogravimetric analysis were used to characterize the structures and thermal stabilities of related compounds. Flame retardation performance of hydrolyzed starch phosphamide from melamine was investigated by UL94, limit oxygen index test, and cone calorimetry. Result shows that the PU/hydrolyzed starch phosphamide from melamine composites with 30.0 php of hydrolyzed starch phosphamide from melamine got a limit oxygen index of 29.0 and UL94-V0 ranking. Heat release rate, rate of smoke release, and total smoke release were decreased distinctly.</p

Exploration of the Hydrogen-Bonded Energetic Material Carbohydrazide at High Pressures

We have reported the high-pressure behavior of hydrogen-bonded energetic material carbohydrazide (CON₄H₆, CHZ) via <i>in situ</i> Raman spectroscopy and angle-dispersive X-ray diffraction (ADXRD) in a diamond anvil cell with ∼15 GPa at room temperature. Significant changes in Raman spectra provide evidence for a pressure-induced structural phase transition in the range of ∼8 to 10.5 GPa. ADXRD experiments confirm this phase transition by symmetry transformation from <i>P</i>2₁/<i>n</i> to a possible space group <i>P</i>1̅, which exhibits ∼23.1% higher density at 10.1 GPa compared to phase <i>P</i>2₁/<i>n</i> at ambient pressure. Moreover, the observed transition is completely reversible when the pressure is totally released. On the basis of the decreased number of hydrogen bonds, the shortened hydrogen bond lengths, and the variations in the NH and NH₂ stretching Raman peaks in the high-pressure phase, we propose that this phase transition is caused by the rearrangement of the hydrogen-bonded networks

New Assembly of Acetamidinium Nitrate Modulated by High Pressure

High pressure is an essential thermodynamic parameter in exploring the performance of condensed energetic materials. Combination of high-pressure techniques and supramolecular chemistry opens a new avenue for synthesis of high energy density materials. Herein, we fabricate a new high-pressure-assisted assembly of energetic material acetamidinium nitrate (C₂N₂H₇⁺·NO₃^–, AN) with <i>P</i>-1 symmetry after a 0–12 GPa–0 treatment at room temperature, which exhibits a density that is 9.8% higher than that of the initial <i>P</i>2₁/<i>m</i> phase. Evolution of intermolecular lattice modes in Raman spectra and synchrotron X-ray diffraction (XRD) patterns provide strong evidence for this transition in the 1.3–3.4 GPa range. The mechanism involves relative motions between ionic pairs in the hydrogen-bonded array and distortions of building blocks

Pressure-Induced Phase Transition in N–H···O Hydrogen-Bonded Molecular Crystal Biurea: Combined Raman Scattering and X‑ray Diffraction Study

The response of biurea to high pressures is investigated by <i>in situ</i> Raman spectroscopy and angle-dispersive X-ray diffraction (ADXRD) in a diamond anvil cell up to ∼5 GPa. Raman scattering measurements indicate a phase transition occurring over the pressure range of 0.6–1.5 GPa. Phase transition is confirmed by changes in the ADXRD spectra with symmetry transformation from <i>C</i>2/<i>c</i> to a possible space group <i>P</i>2/<i>n</i>. Upon total release of pressure, the diffraction spectrum returns to its initial state, which implies that the transition observed is reversible. We discuss variations in the Raman spectra, including splitting of modes, appearance of new modes, and abrupt changes in the slope of the frequency shift curves at several pressures. We propose that the phase transition observed in this study is attributed to rearrangement of the hydrogen-bonded networks

<i>Gauche</i>–<i>trans</i> Conformational Equilibrium of Succinonitrile under High Pressure

Organic chain molecules have considerable importance because of their conformational stability, which is fundamental to their chemical stability. The phase behaviors and conformational equilibrium of simple hydrocarbons and their derivatives under extreme conditions are of interest to research because of their applications. In situ high-pressure Raman spectroscopy studies on succinonitrile up to 24 GPa at ambient temperature have been conducted to investigate its structural properties and conformational equilibria. Succinonitrile has undergone a plastic-to-crystal phase transition around 0.7 GPa. A simultaneous conversion of <i>gauche</i> to <i>trans</i> conformation has been observed. A crystal-to-crystal phase transition has subsequently occurred around 2.9 GPa. The second high-pressure phase has remained stable up to 24 GPa. These two crystal structural transitions have also been confirmed by in situ high-pressure angle-dispersive X-ray diffraction experiments. Compared with the reported low-temperature phase, the new phases under high pressure have different molecular conformations and higher densities, which can provide better understanding of the paths of conformational transitions under different extreme conditions

Genome-Scale Transcriptome Analysis of the Alpine “Glasshouse” Plant <i>Rheum nobile</i> (Polygonaceae) with Special Translucent Bracts

<div><p>Background</p><p><i>Rheum nobile</i> is an alpine plant with translucent bracts concealing the inflorescence which produce a “glasshouse” effect promoting the development of fertile pollen grains in such conditions. The current understanding of the adaptation of such bracts to alpine environments mainly focuses on the phenotypic and physiological changes while the genetic basis is very limited. By sequencing the upper bract and the lower rosulate leaf from the same <i>R. nobile</i> stem, we identified candidate genes that may be involved in alpine adaption of the translucent bract in “glasshouse” plants and illustrated the changes in gene expression underlying the adaptive and complex evolution of the bracts phenotype.</p><p>Results</p><p>A total of 174.2 million paired-end reads from each transcriptome were assembled into 25,249 unigenes. By comparing the gene expression profiles, we identified 1,063 and 786 genes up-regulated respectively in the upper bract and the lower leaf. Functional enrichment analyses of these genes recovered a number of differential important pathways, including flavonoid biosynthesis, mismatch repair and photosynthesis related pathways. These pathways are mainly involved in three types of functions: 9 genes in the UV protective process, 9 mismatch repair related genes and 88 genes associated with photosynthesis.</p><p>Conclusions</p><p>This study provides the first comprehensive dataset characterizing <i>Rheum nobile</i> gene expression at the transcriptomic scale, and provides novel insights into the gene expression profiles associated with the adaptation of the “glasshouse” plant bracts. The dataset will be served as a public genetic resources for further functional and evolutionary studies of “glasshouse” plants.</p></div