•Carbamazepine crystallization with different molecular weight polyethylene glycol was studied.•An effective method for stabilizing metastable crystal form was proposed.•Increasing the molecular ...weight of the polyethylene glycol additive decreased the aspect ratio of crystal.
The effect of polyethylene glycol (PEG) with different molecular weights on carbamazepine (CBZ) crystallization was investigated by experiments and molecular dynamics (MD) simulations. The influence of PEG on the crystal morphology and solvent-mediated phase transition of CBZ was studied. It was found that PEG inhibited the CBZ III nucleation and CBZ II transition. The crystal morphology changes significantly from needle to rod when adding PEG with a molecular weight greater than 1500. MD simulations show that the binding energy sequence between the additive and the crystal surface is: Eb(1 –1 –1) > Eb(2 –2 1) > Eb(2 –1 0), which explains the suppression of axial crystal growth. The results provide a possible method to stabilize the metastable crystal form of CBZ and improve crystal morphology.
Zn(salen) nano-complex was synthesized by facile hydro/solvothermal route in water as green solvent at various times and temperatures without using any surfactant or capping agent. The morphology of ...the products varied from irregular microcrystals to nanosheets by adjusting the temperature and time of the reaction. Based on the growth process with respect to the morphological structure, a novel growth mechanism is revealed which involves a unique multistep pathway, including reaction–nucleation, aggregation, crystallization, dissolution–recrystallization, and Ostwald ripening. The photoluminescence properties of the compounds were also examined and exhibited strong fluorescence emissions.
•Synthesis of Zn(salen) nano-complex for the first time.•Use of green solvent for the synthesis of coordination compound.•Represent a reasonable mechanism for growth of crystals.
This paper focuses on the multi-dimensional performance analysis including the oxidation performance, crystal morphology, thermal properties, mechanical properties and dielectric behavior of the ...thermally aged extra high voltage XLPE submarine cable insulation. Results show that the antioxidation and thermal oxidative aging of XLPE insulation are coexisting and competing during the thermal degradation process. In the early stage of thermal degradation, the antioxidation of XLPE insulation is dominant resulting in the decline of the spacing between spherulites. In the later stage of thermal degradation, thermally oxidative aging of XLPE insulation is dominant, which leads to the damage of the crystalline morphology and the rapid generation of aging products. It is indicated that the mechanical strength of the XLPE insulation is mainly determined by its internal crystalline morphology, while the dielectric properties of the XLPE insulation are governed by the crystalline morphology, aging products and micro interface. With the thermal aging time extended, the breakdown strength of XLPE insulation first increases and then decreases, which is determined by its amorphous region and aging products.
The crystal morphology of high energetic materials plays a crucial role in aspects of their safety performance such as impact sensitivity. In order to reveal the crystal morphology of ammonium ...dinitramide/pyrazine-1,4-dioxide (ADN/PDO) cocrystal at different temperatures, the modified attachment energy model (MAE) was used at 298, 303, 308, and 313 K to predict the morphology of the ADN/PDO cocrystal under vacuum and ethanol. The results showed that under vacuum conditions, five growth planes of the ADN/PDO cocrystal were given, which were (1 0 0), (0 1 1), (1 1 0), (1 1 -1), and (2 0 -2). Among them, the ratios of the (1 0 0) and (0 1 1) planes were 40.744% and 26.208%, respectively. In the (0 1 1) crystal plane, the value of S was 1.513. The (0 1 1) crystal plane was more conducive to the adsorption of ethanol molecules. The order of binding energy between the ADN/PDO cocrystal and ethanol solvent was (0 1 1) > (1 1 -1) > (2 0 -2) > (1 1 0) > (1 0 0). The radial distribution function analysis revealed that there were hydrogen bonds between the ethanol and the ADN cations, van der Waals interactions with the ADN anions. As the temperature increased, the aspect ratio of the ADN/PDO cocrystal was reduced, making the crystal more spherical, which helped to further reduce the sensitivity of this explosive.
Competitive growth of converging dendrites in directional solidification was investigated by in situ observation in a succinonitrile–acetone alloy. The specific dendrite growth behavior was analyzed ...and compared with the results of phase field simulations. It is found that the growth of the well aligned grain boundary dendrite is retarded and the spacing between this dendrite and its immediate neighbors (λGB1) decreases continuously as the misaligned dendrites get to the grain boundary, one by one. The anomalous overgrowth only happens when the spacing λGB1 decreases to certain level. Under the same solidification condition, smaller initial primary spacing makes the anomalous overgrowth take place earlier and more frequently.
•in situ observation was carried out in a transparent alloy of SCN–2wt%Ace.•The specific competition process of converging growth is clearly shown.•Solute interaction decreases the primary dendrite spacing at the grain boundary.•The lag of well aligned GB dendrite is a key factor to the anomalous overgrowth.•It occurs earlier and more frequently with smaller initial primary spacing.
The limited applications of ZnO in the visible light are still a challenge. In a short-term reaction (15 min), controlling the growth and morphology of zinc oxide in nano-structures had been achieved ...using a domestic microwave as a simple, quick and inexpensive tool. Besides, no seeds substrates were needed to be immersed during preparation process. Adding capping or complexing agents helped in controlling the surface morphology of ZnO, like hexamethylenetetramine, poly(vinyl pyrrolidone) (Polyvinyl alcohol), Hydrazine hydrate, trisodium citrate and ethylenediamine. The XRD results indicated the crystalline hexagonal wurtzite phase for all ZnO samples showing crystallite size ranged from 16.8 to 31.2 nm. SEM photos for the prepared ZnO NS samples demonstrated morphologies of twin-short rod, hexagonal rod, nanowires, nanosheet, and nanoflower structures. UV–visible and PL spectroscopy for measuring the optical properties showed that the band gap of ZnO samples ranged between 3.25 and 3.21 eV and still smaller than the standard value. Sample (M2) showed the highest intensity peak at 438 nm and high broad green emission peak at 511 nm. In brief, both solvent nature and crystal growth in the specific solvents are the keys to enforcing the crystal morphology. Eventually, the antibacterial activity of zinc oxide was evaluated in the presence and absence of UV radiation. Findings showed that all aqueous solution of ZnO samples irradiated by UV exhibit more antibacterial activity due to the increased amount of H2O2 generated which is fatal to bacteria.
•Improving optical and catalytic activity in the visible light remains a challenge.•ZnO NS prepared by household microwave at low power (200 Watt) within 15 min.•Addition of capping or complexing agent changed the growth of crystalline ZnO.•Morphology was twin short rod, hexagonal rod, wire, nanosheet & nanoflower forms.•ZnO nanostructures exhibit anti bacterial activity under or without activated by UV.
The presence of alcohol in binary alcohol–water mixtures can affect the precipitation pathways of anhydrous crystalline CaCO3 polymorphs and their morphology. We explored the formation pathways and ...the effects of several parameters on calcite, vaterite, and aragonite: concentration of simple alcohols, time, and shaking speed, and we derived a multiparameter model for predicting what phase is preferred. We found that shaking speed and alcohol concentration are the most important parameters for affecting the stability of vaterite and aragonite and for changing vaterite morphology, from cauliflower-shaped, spherical aggregates, to dendritic, flatter structures. In all our experiments, the precipitated aragonite was twinned, and both the vaterite and aragonite can be interpreted to form through spherulitic growth. Classical growth theory fully describes their formation; there is no need to invoke the popular hypothesis for nonclassical growth by self-assembly of nanocrystals. These studies, and future work with solutions of low water activity, are paving the way to a better understanding of how organisms select their preferred polymorph and engineer CaCO3 morphology during biomineralization.
2D Si nanomaterials draw great interest owing to their fascinating properties and potential applications in electronic devices, catalysts, and energy storage and conversion devices. However, ...high‐quality and large‐scale synthesis of Si nanosheets remains a big challenge, despite the limited reports on their preparations via chemical exfoliation of layered Zintl silicide, magnesiothermic reduction of layered silicon oxide, and chemical vapor deposition. In this work, a facile, solution method to produce free‐standing Si nanosheets in high yields and low cost, based on the reaction of commercial magnesium powder with trichlorosilane and tripropylamine in dichloromethane under mild conditions, is reported. The prepared Si nanosheets have an average thickness of ≈2 nm and show photoluminescence. Experiments demonstrate that the key to the formation of Si nanosheets is the use of dichloromethane as a solvent. This method can be used to prepare Si nanosheets in large scale for various potential applications and possibly Si crystals with specific crystal morphology.
A facile, solution method is developed to produce free‐standing Si nanosheets in high yields and low cost, based on the reaction of commercial magnesium powder with trichlorosilane and tripropylamine in dichloromethane under mild conditions. The prepared Si nanosheets have an average thickness of ≈1.5–2 nm and show photoluminescence.
Due to the linear and ultra-long molecular chains, ultra-high molecular weight polyethylene (UHMWPE) has been playing a vital role in many fields. Based on more and more demands for special UHMWPE ...resins, the relationship between microstructure of nascent powder and its corresponding physical properties was investigated in this work, and one special powder with high degree of short-chain branch was fully contrasted with one general-purpose UHMWPE resin. Based on series characterization results, it revealed that short-branched chains led to a decrease on the entanglement density and brought a significant increase in the processing performance and mechanical properties. In addition, the short-branched chains also made a huge difference on crystal morphology of nascent UHMWPE powders. By correlating high-resolution scanning electron microscopy, DSC curves and Raman spectroscopy characteristics, the slurry polymerization mechanism of UHMWPE was deduced, and the corresponding performance of nascent UHMWPE powders was fully explained.
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•Short-branched chains brought UHMWPE resin a distinct crystal morphology that consisted of fewer fibrils than linear UHMWPE.•Short-branched chains reduced the entanglement density of UHMWPE nascent powder.•Short-branched chains improved the process-ability and mechanical properties of UHMWPE resin.
Spherical and polycrystalline particles of vaterite precipitated from solution has been shown to grow by crystal growth of a spherulitic type, and not by aggregation of nano-sized precursor crystals ...as often claimed in the literature. The mixing of concentrated solutions of calcium nitrate and sodium carbonate resulted in the formation of amorphous calcium carbonate which transforms within minutes to produce crystalline vaterite. Vaterite spheres nucleate and grow at a moderate relative supersaturation ratio of σ ≅ 5, determined by the dissolution of the amorphous compound. The size of the resulting vaterite spherulites is accounted for by the crystal growth rate determined in absence of nucleation, which disproves the nano-aggregation mechanism. The inner structure of fractured vaterite spheres exhibit the radiating pattern characteristic for spherulitic crystal growth. The final numbers of vaterite spherulites are typical for heterogeneous nucleation processes. It would take supersaturation values, orders of magnitude higher, to obtain the particle numbers required for the proposed nano-aggregation process.
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