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A novel approach to coat silica on quantum dots: Forcing decomposition of tetraethyl orthosilicate in toluene at high temperature
摘要： The coating of silica (SiO2) on quantum dots (QDs) has been widely studied, because SiO2 can protect QDs from the damages of moisture, radiation, and heat. Conventional SiO2 coating methods for QDs are usually performed in aqueous or emulsion solutions, which require the addition of water for the hydrolysis of SiO2 precursors and lead to the photoluminescence (PL) quenching of QDs. To address this issue, a novel SiO2 coating approach on single particle level was developed by the thermally forcing decomposition of tetraethyl orthosilicate in toluene. The CdSe/CdS/ZnS:Al@SiO2 nanoparticles (NPs) were prepared without decreasing the original PL quantum yield (QY), which exhibited much better photo and thermal stability in comparison with uncoated CdSe/CdS/ZnS:Al QDs. Furthermore, due to the natural formation of silanol groups on the SiO2 shell, CdSe/CdS/ZnS:Al@SiO2 NPs present not only good solubility but also excellent room temperature stability in phosphate buffer saline solution for several months.
关键词： SiO2,TEOS,stability,core/shell quantum dots,water solubility
更新于2025-09-11 14:15:04
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Determination of the phase relation of a Li La(1?)/3NbO3 system by the slow cooling floating zone method
摘要： The phase relation during cooling of molten LixLa(1?x)/3NbO3 (LLN) was investigated by the slow cooling ?oating zone (SCFZ) method. It was found that LLN melts incongruently into LaNbO4 and a liquid. From the results of an electron probe microanalysis (EPMA) of the SCFZ samples, the solubility limit of Li into LLN was estimated to be x = 0.29, and the distribution coe?cient of Li into LLN appeared to be 0.54. The melting temperatures of LLN with various Li content were determined by di?erential thermal analysis. The results of the present work could be valuable for the growth of high-quality LLN single crystals.
关键词： Lithium compounds,Solubility,Oxides,Slow cooling ?oating zone,Phase diagrams,Lanthanum lithium niobate
更新于2025-09-10 09:29:36
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Solubility and H-bonding of poly(vinylidene fluoride) copolymers in carbonyl liquids: Experiment and molecular simulation
摘要： H-bond formation among fluoropolymers and carbonyl solvents was studied by microcalorimetry and quantum chemistry simulation. Typically, fluorine atoms in organic molecules depress their ability to molecular interactions with solvents. Meanwhile, it is not the case if fluoropolymer is dissolved in carbonyl solvent. Among other organic solvents carbonyl-containing liquids are characterized by very large exothermic effects of dissolution of vinylidene fluoride copolymers which are typical for the systems with electron-donor-acceptor complexes. The enthalpy of mixing in the entire concentration range was determined for P(VDF-co-HFP) and P(VDF-co-CTFE) solutions in ethyl acetate and Flory-Huggins parameter was evaluated. It was ?1.31, which means very strong interaction among solvent and vinylidene fluoride monomer units. This interaction was modeled by quantum chemistry semi-empirical AM1, PM3, PM5 and density functional B88-PW91, B88-LYP, D-VWN calculations for the complexes between acetone or ethyl acetate and vinylidene fluoride tetramer. The heat of formation of the complex from its components was found around ?18 kJ/mol. The binding site of the complex was a macrocyclic structure which comprised H-bonds between carbonyl and methylene hydrogens of vinylidene fluoride backbone, and weaker H-bonds between fluorine atoms and methyl hydrogen. The analysis of molecular orbitals of the complex reveals extended electron delocalization across the binding center.
关键词： Calorimetry,H-bonding,Computer modeling,Solubility of vinylidene fluoride copolymers
更新于2025-09-10 09:29:36
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A universal method for large-yield and high-concentration exfoliation of two-dimensional hexagonal boron nitride nanosheets
摘要： Hexagonal boron nitride (hBN) is an ultra-wide bandgap insulating material, which possesses a graphite-like layered structure, and the two-dimensional (2D) hexagonal boron nitride nanosheets (hBNNS), exfoliated from the bulk hBN, have promising applications in electronic packaging and high-power devices, due to the high thermal conductivity, excellent thermal/chemical stability as well as the ultra-wide band gap. However, the exfoliation of hBNNS is still a challenge with respect to high cost, time consuming, and low yield. Herein, a facile hydrothermal exfoliation method was proposed for the first time to exfoliate the hBNNS in a large yield and high concentration. In the optimized hydrothermal conditions, the lithium ion (Li+) intercalation, isopropanol (IPA) solvent, and the strong stirring could give rise to a large exfoliation yield up to (cid:1)55% and a high concentration (cid:1)4.13 mg/mL. In addition, the exfoliated hBNNS could enhance the methyl orange (MO) photodegradation efficiency of TiO2 from 91% to 96.4 %. Most importantly, this hydrothermal exfoliation method could be a universal approach for the exfoliation of 2D materials.
关键词： Hydrothermal exfoliation,Nanosheets,2D materials,Hexagonal boron nitride,Solubility parameters theory,Universal approach
更新于2025-09-10 09:29:36
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摘要： One commonly used system to study morphology development in multi-phase, multi-component alloys is directionally solidified ternary eutectic Al-Ag2Al-Al2Cu. One challenge in studying this system is a relatively large solubility shift of the chemical element Ag in the Al-phase after solidification, which significantly affects the observed phase fractions. The effects of this change on the microstructural patterns are not yet understood. To study these effects, directionally solidified samples of ternary eutectic Al-Ag2Al-Al2Cu were quenched, sectioned and subjected to systematic annealing. This allowed the microstructure evolution at the quenched solid-liquid interface to be recorded in cross section and quantitatively analyzed. The results show that the phase fraction changes in the micrographs are in good accordance with theoretical predictions from the thermodynamic Calphad database. Different microstructural patterns show distinct responses to the annealing. For a more highly ordered chain-like structure, the pattern is preserved even after 32 h at more than 96% of the melting temperature, as determined by the constant number and size of the intermetallic rods in the micrographs. For a less ordered cross-type structure, coarsening of the microstructure is observed, resulting in a pattern change. The outcomes underline the importance of considering post-solidification effects during the investigation of ternary eutectic Al-Ag2Al-Al2Cu and help to improve the understanding of the microstructure arrangement in complex eutectic alloys.
关键词： A1. Directional solidification,A1. Diffusion,A1. Eutectics,A1. Solubility,B1. Metals
更新于2025-09-10 09:29:36
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Modification of Phosphoryl Substituents of Phthalocyanines As a Route to Targeted Tuning of Lipophilic-Hydrophilic Properties
摘要： О?,О?-Diethyl-[2-(3,4-dicyanophenoxy)phenyl]phosphonate has been synthesized for the first time and introduced in template condensation on lithium and zinc cations to prepare a series of new neutral and acidic phthalocyanines containing four fragments of 2-oxyphenylphosphonic acid. A scheme of modification of the peripheral substituents at the phosphoryl group was developed allowing a targeted synthesis of phthalocyanine ligands and complexes soluble in organic solvents or aqueous media.
关键词： aggregation in solution,solubility in water,phosphoryl-containing substituents,phthalocyanines,2-oxyphenylphosphonic acid
更新于2025-09-10 09:29:36
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Paracetamol micro-structure analysis by optical mapping
摘要： Domain structure of paracetamol - popular antipyretic analgesic - was investigated by infrared (IR) spectroscopy using synchrotron radiation. Absorbance and retardance maps reveal molecular orientation inside the micro-domains of the paracetamol form II which has a better water solubility and compressibility compared to the commercially used forms I. The developed method of analysis representing orientation of optical slow(fast)-axis is compared with azimuthal orientation of the absorbance at several specific IR bands using vector maps. High brightness of synchrotron radiation and hyper-spectral mapping of structural domains in paracetamol clearly reveals the domain boundaries and can potentially be used to observe in situ intra-phase transformations of paracetamol forms-I, II, III and melting, which are important for making medical tablets and powders by an industrial process.
关键词： Paracetamol,Water solubility,Retardance,Orientational anisotropy,Absorbance
更新于2025-09-04 15:30:14
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Organosoluble and transparent cardo polyimides with high <i>T</i> <sub/>g</sub> derived from 9,9-bis(4-aminophenyl)xanthene
摘要： 9,9-Bis(4-aminophenyl)xanthene (BAPX) was prepared simply and effectively via one-pot, two-step procedure using xanthenone and aniline as main substrates. The monomer BAPX was reacted with six aromatic dianhydrides in N,N-dimethylacetamide (DMAc) to yield the corresponding polyimides (PIs) via the poly(amic acid) precursors and subsequent thermal or chemical imidization. The resulting PIs exhibited good thermal stability with glass transition temperatures of 308–348°C, initial decomposition temperatures of 470–510°C, 10% weight loss temperatures of 540–565°C, and char yields of 55–59% at 800°C in nitrogen, respectively. All polymers were amorphous and readily soluble in organic solvents such as N-methyl-2-pyrrolidone and DMAc. The PI films had tensile strengths of 71–92 MPa, tensile moduli of 1.91–2.35 GPa, and elongations at break of 5–13%. Meanwhile, these polymer films also had high optical transparency with a cutoff wavelength in the range of 367–415 nm, lower dielectric constants (3.02–3.34 at 10 MHz), and low water uptake of 0.30–0.52%.
关键词： Aromatic polyimide,9,9-bis(4-aminophenyl)xanthene,bulky pendent xanthene cardo group,thermal property,optical transparency,solubility
更新于2025-09-04 15:30:14
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Cs Oleate Precursor Preparation for Lead Halide Perovskite Nanocrystal Synthesis: The Influence of Excess Oleic Acid on Achieving Solubility, Conversion, and Reproducibility.
摘要： In the colloidal synthesis of inorganic perovskite materials, cesium oleate (CsOL) is the most commonly used Cs precursor. Yet despite its ubiquitous use in literature, CsOL has been observed to be insoluble at room temperature and leads to surprisingly inconsistent results in CsPbX3 nanocrystal synthesis depending on the Cs salt from which the precursor is derived. We show that under the conditions used in most reports, the amount of oleic acid (OA) added, while stoichiometrically sufficient, still leads to incomplete conversion of the Cs salts to CsOL. This results in a mixture of Cs sources being present during the reaction, causing decreased homogeneity and reproducibility. When a 1:5 Cs:OA ratio is used, complete conversion is readily obtained even under mild conditions, resulting in a precursor solution that is soluble at room temperature and yields identical synthetic results regardless of the initial Cs source. Further, 1H nuclear magnetic resonance (NMR) of solutions prepared using varying Cs:OA ratios shows that the maximum ratio of Cs:OA obtainable in solution is 1:5, with any excess Cs present in the precipitate. We believe the use of a soluble, fully converted CsOL reagent will improve reproducibility for Cs-based perovskite synthesis and directly benefit synthetic methods based on microfluidics.
关键词： reproducibility,inorganic perovskite materials,microfluidics,CsPbX3 nanocrystal synthesis,colloidal synthesis,oleic acid,solubility,cesium oleate
更新于2025-09-04 15:30:14