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31.
There is growing evidence that the flow of driven amorphous solids is not homogeneous, even if the macroscopic stress is constant across the system. Via event-driven molecular dynamics simulations of a hard sphere glass, we provide the first direct evidence for a correlation between the fluctuations of the local volume fraction and the fluctuations of the local shear rate. Higher shear rates do preferentially occur at regions of lower density and vice versa. The temporal behavior of fluctuations is governed by a characteristic time scale, which, when measured in units of strain, is independent of shear rate in the investigated range. Interestingly, the correlation volume is also roughly constant for the same range of shear rates. A possible connection between these two observations is discussed. 相似文献
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The unison of vegetable oil‐based hyperbranched polymers with nanotechnology can unhook myriad of avant‐garde applications of such materials. Thus Mesua ferrea L. seed oil‐based hyperbranched polyurethane (HBPU)/clay nanocomposites and their performance, with special reference to adhesive strength, are reported for the first time. The nanocomposites of the hyperbranched polyurethane with organically modified nanoclay were obtained by ex situ solution technique and cured by bisphenol‐A‐based epoxy with poly(amido amine) hardener system. The partially exfoliated and well‐distributed structure of nanoclay was confirmed by XRD, SEM, and TEM studies. FTIR spectra indicate the presence of H‐bonding between nanoclay and the polymer matrix. Two times improvement in the adhesive strength and scratch hardness, 10 MPa increments in the tensile strength and 112°C more thermo‐stability have been observed without much affecting the impact resistance, bending, and elongation at break of the nanocomposites compared to the pristine epoxy modified HBPU system. Thus, the resulted nanocomposites are promising materials for different advanced applications including adhesive. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Sibel Demir Kanmazalp Eyüp Başaran Ayşegül Karaküçük-Iyidoğan Emine Elçin Oruç-Emre Fatih Şen Necmi Dege 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):675-684
AbstractThe molecule (?)-(S)-1-[2-(benzenesulfonamido)-3-phenylpropanoyl]-4-[(4-methyl)phenyl] thiosemicarbazide was synthesized and its structure analyzed by X-ray diffraction to understand its geometry, and inter/intra-molecular interactions. Theoretical calculations were carried out using DFT and TD-DFT methods with B3LYP/6-31G(d, p) and B3LYP/6-31G?+?(d, p) basis sets. Theoretical bond parameters, harmonic vibration frequencies, and chemical shifts are in good agreement with the experimental results. Electronic properties of the molecule derived from frontier orbitals, molecular electrostatic potential, and theoretical UV-Visible spectrum are validated experimentally. 相似文献
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Dr. Suvendu Sekhar Mondal Dr. Asamanjoy Bhunia Ahmed G. Attallah Dr. Philipp R. Matthes Alexandra Kelling Prof. Uwe Schilde Prof. Klaus Müller‐Buschbaum Prof. Reinhard Krause‐Rehberg Prof. Christoph Janiak Prof. Hans‐Jürgen Holdt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6905-6913
An extended member of the isoreticular family of metal–imidazolate framework structures, IFP‐6 (IFP=imidazolate framework Potsdam), based on cadmium metal and an in situ functionalized 2‐methylimidazolate‐4‐amide‐5‐imidate linker is reported. A porous 3D framework with 1D hexagonal channels with accessible pore windows of 0.52 nm has been synthesized by using an ionic liquid (IL) linker precursor. IFP‐6 shows significant gas uptake capacity only for CO2 and CH4 at elevated pressure, whereas it does not adsorb N2, H2, and CH4 under atmospheric conditions. IFP‐6 is assumed to deteriorate at the outside of the material during the activation process. This closing of the metal–organic framework (MOF) pores is proven by positron annihilation lifetime spectroscopy (PALS), which revealed inherent crystal defects. PALS results support the conservation of the inner pores of IFP‐6. IFP‐6 has also been successfully loaded with luminescent trivalent lanthanide ions (LnIII=Tb, Eu, and Sm) in a bottom‐up one‐pot reaction through the in situ generation of the linker ligand and in situ incorporation of photoluminescent Ln ions into the constituting network. The results of photoluminescence investigations and powder XRD provide evidence that the Ln ions are not doped as connectivity centers into the frameworks, but are instead located within the pores of the MOFs. Under UV light irradiation, Tb@IFP‐6 and Eu@IFP‐6 (λexc=365 nm) exhibit observable emission changes to a greenish and reddish color, respectively, as a result of strong Ln 4 f emissions. 相似文献
35.
An inexpensive and readily available ionic liquid, tetrabutylammonium bromide in the molten state, efficiently catalyzes the conjugate addition of thiols to α,β-unsaturated nitriles, carboxylic ester, ketones and aldehydes as well as nitro olefins. 相似文献
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A new method for the synthesis of Spiro dibenzo[b,e][1,4]oxazepines that involves a three‐component reaction of isatins, 2‐amino phenols and cyclic‐1,3‐diketones has been developed. This protocol employs Na‐Y zeolite nanopowder as a heterogeneous catalyst and does not require the presence of any additivies or strong acid–base condition. Na‐Y zeolite nanopowder was synthesized through a simple hydrothermal procedure and it was characterized using different array of shophisticated techniques. Key features of the reaction include a recyclable catalyst and a wide scope of possible substrates. 相似文献
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Moumita Pait Gargi Kundu Srinu Tothadi Suvendu Karak Shailja Jain Kumar Vanka Sakya S. Sen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(9):2830-2834
The reaction of SIPr, [1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene] ( 1 ), with C6F6 led to the formation of an unprecedented mesoionic compound ( 2 ). The formation of 2 is made accessible by deprotonation of the SIPr backbone with simultaneous elimination of HF. The C?F bond para to the imidazolium ring in 2 is only of 1.258(4) Å, which is the one of the shortest structurally authenticated C?F bonds known to date. The liberation of HF during the reaction is unequivocally proved by the addition of one more equivalent of SIPr, which leads to the imidazolium salt with the HF2? anion. To functionalize 2 , the latter reacted with B(C6F5)3 to give an unusual donor–acceptor compound, where the fluoride atom from the C6F5 moiety coordinates to B(C6F5)3 and the carbanion moiety remains unaffected. Such coordination susceptibility of the fluoride atom of a nonmetallic system to a main‐group Lewis acid (Fnon‐metal→BR3) is quite unprecedented. 相似文献
39.
Magnetic iron nanoparticles are attracting a great deal of research and application interest in diversified fields. In this present investigation, iron nanoparticles were prepared by a in-situ chemical reduction technique in a combination of polyaniline (PANI)-polyacrylamide (PA) and PANI-hyperbranched polyurethane (HBPU) matrices to judge the suitability of hyperbranched system. The formation of the nanoparticles in polymer matrices has been investigated by FTIR, UV, XRD, SEM and TEM studies. Narrower size with better dispersion and more stable nanoparticles were found in a hyperbranched matrix system compared to a linear one. The particle size was found to be in the range of 10–20 nm and 12–35 nm in HBPU-PANI and PA-PANI matrices, respectively. Both the nanocomposites exhibit synergistic free radical scavenging capability towards 2,2-diphenyl-1-picrylhydrazyl (DPPH). The magnetic hysteresis loop of the nanocomposites indicates the super-paramagnetic behavior. The hyperbranched system is more thermostable than the linear system by 70°C. 相似文献
40.
Ultrastable Imine‐Based Covalent Organic Frameworks for Sulfuric Acid Recovery: An Effect of Interlayer Hydrogen Bonding 下载免费PDF全文
Arjun Halder Suvendu Karak Dr. Matthew Addicoat Saibal Bera Dr. Amit Chakraborty Shebeeb H. Kunjattu Dr. Pradip Pachfule Prof. Dr. Thomas Heine Prof. Dr. Rahul Banerjee 《Angewandte Chemie (International ed. in English)》2018,57(20):5797-5802
A rapid and scalable synthesis of six new imine‐linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H2SO4 (18 m ), conc. HCl (12 m ), and NaOH (9 m ). This is because of the presence of strong interlayer C?H???N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (?C=N?) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self‐standing, and crack‐free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as‐synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm?2 h?1 bar?1) and acetone (260 Lm?2 h?1 bar?1). 相似文献