The Experts below are selected from a list of 85962 Experts worldwide ranked by ideXlab platform
Huamin Zhang - One of the best experts on this subject based on the ideXlab platform.
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Xianfeng Li, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp2 hybrid orbital interactions between pyridinic-nitrogen in 4,4′-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4′-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydroc...
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp(2) hybrid orbital interactions between pyridinic-nitrogen in 4,4'-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4'-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydrocarbon ion exchange membranes for VFB.
Donald E Williams - One of the best experts on this subject based on the ideXlab platform.
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improved intermolecular force field for molecules containing h c n and o atoms with application to nucleoside and peptide crystals
Journal of Computational Chemistry, 2001Co-Authors: Donald E WilliamsAbstract:A new intermolecular force field for nitrogen atoms in organic molecules was derived from a training dataset of 76 observed azahydrocarbon crystal structures and 11 observed heats of sublimation. The previously published W99 force field for hydrogen, carbon, and oxygen was thus extended to include nitrogen atoms. Nitrogen atoms were divided into four classes: N(1) for triply bonded nitrogen, N(2) for nitrogen with no bonded hydrogen (except the triple bonded case), N(3) for nitrogen with one bonded hydrogen, and N(4) for nitrogen with two or more bonded hydrogens. H(4) designated hydrogen bonded to nitrogen. Wavefunctions of 6-31g** quality were calculated for each molecule and the molecular electric potential (MEP) was modeled with net atomic and supplementary site charges. Lone pair Electron charge sites were included for nitrogen atoms where appropriate, and methylene bisector charges were used for CH2 and CH3 groups when fitting the MEP. XH bond distances were set to standard values for the wave function calculation and then foreshortened by 0.1 A for the MEP and force field fitting. Using the force field optimized to the training dataset, each azahydrocarbon crystal structure was relaxed by intermolecular energy minimization. Predicted maximum changes in unit cell edge lengths for each crystal were 3% or less. The complete force field for H, C, N, and O atoms was tested by intermolecular energy relaxation of nucleoside and peptide molecular crystals. Even though these molecules were not included in any of the training datasets for the force field, agreement with their observed crystal structures was very good, with predicted unit cell edge shifts usually less than 2%. These tests included crystal structures of representatives of all eight common nucleosides found in DNA and RNA, 15 dipeptides, four tripeptides, two tetrapeptides, and a pentapeptide with two molecules in the asymmetric unit. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1154–1166, 2001
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spherical and aspherical intermolecular force fields for sulfur allotropes
Inorganic Chemistry, 1999Co-Authors: Aron Abraha, Donald E WilliamsAbstract:Elemental sulfur exists in many crystalline forms, with many of these forms being composed of discrete Sn cyclic molecules. Eleven experimentally determined Sn crystal structures are used to define a new spherical S···S intermolecular force field of the (exp-6) type. Evidence is presented that the bonded sulfur atom in these structures is not spherical. The asphericity was modeled by placing repulsion bumps at optimized locations on the sulfur atoms to represent lone pair Electron repulsion. The bump locations deviate from perfect tetrahedral geometry, being located more perpendicular to the S−S−S plane. A new aspherical sulfur intermolecular force field was derived from eleven Sn crystal structures. The aspherical force field gives an improved prediction of the Sn crystal structures.
Zhizhang Yuan - One of the best experts on this subject based on the ideXlab platform.
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Xianfeng Li, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp2 hybrid orbital interactions between pyridinic-nitrogen in 4,4′-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4′-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydroc...
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp(2) hybrid orbital interactions between pyridinic-nitrogen in 4,4'-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4'-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydrocarbon ion exchange membranes for VFB.
Yuyue Zhao - One of the best experts on this subject based on the ideXlab platform.
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Xianfeng Li, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp2 hybrid orbital interactions between pyridinic-nitrogen in 4,4′-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4′-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydroc...
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mechanism of polysulfone based anion exchange membranes degradation in vanadium flow battery
ACS Applied Materials & Interfaces, 2015Co-Authors: Zhizhang Yuan, Yuyue Zhao, Huamin ZhangAbstract:The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp(2) hybrid orbital interactions between pyridinic-nitrogen in 4,4'-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in Electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair Electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4'-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydrocarbon ion exchange membranes for VFB.
Li-dong Zhao - One of the best experts on this subject based on the ideXlab platform.
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Anharmoncity and low thermal conductivity in thermoelectrics
Materials Today Physics, 2018Co-Authors: Cheng Chang, Li-dong ZhaoAbstract:The thermoelectric (TE) efficiency is evaluated by the material thermoelectric figure of merit (ZT), which can be usually improved by enhancing the electrical transport properties and/or reducing the thermal conductivity. Seeking the material with low thermal conductivity is crucial for thermoelectrics, which enable us simplify complex thermoelectric parameters and focus on the optimization of electrical transport properties alone. Here, we summarized the relationship between anharmonicity and low thermal conductivity in thermoelectrics. Several strategies which yield anharmonicity are also suggested, including lone pair Electron, resonant bonding and rattling model. At last, some intuitive methods were proposed and summarized to evaluate the anharmonicity.
