Various soluble hydrophilic macroions can self-assemble into hollow, spherical, monolayered supra... more Various soluble hydrophilic macroions can self-assemble into hollow, spherical, monolayered supramolecular "blackberry"-type structures, despite their like-charged nature. However, how the 3-D symmetrical macroions prefer to form 2-D monolayers in bulk solution, especially for the highly symmetrical "Keplerate" polyoxometalates and functionalized C macroions has been a mystery. Through molecular dynamics simulations, using a model specifically designed for macroions in solution, the mechanism of this intriguing symmetry-breaking process is found to be related to the apparently asymmetric charge distribution on the surface of macroions in the equatorial belt area (the area which can be effectively involved in the counterion-mediated attraction). As a result, the electric field lines around macroions during the self-assembly process clearly show that the symmetry-breaking happens at the dimer level effectively defining the plane of the self-assembly. These findings...
New experiments show that tensile stress vanishes shortly after preyield deformation of polymer g... more New experiments show that tensile stress vanishes shortly after preyield deformation of polymer glasses while tensile stress after postyield deformation stays high and relaxes on much longer time scales, thus hinting at a specific molecular origin of stress in ductile cold drawing: chain tension rather than intersegmental interactions. Molecular dynamics simulation based on a coarse-grained model for polystyrene confirms the conclusion that the chain network plays an essential role, causing the glassy state to yield and to respond with a high level of intrachain retractive stress. This identification sheds light on the future development regarding an improved theoretical account for molecular mechanics of polymer glasses and the molecular design of stronger polymeric materials to enhance their mechanical performance.
Angewandte Chemie (International ed. in English), Mar 15, 2017
We report herein an interesting dynamic translocation process of countercations around one polyox... more We report herein an interesting dynamic translocation process of countercations around one polyoxometalate(POM)-organic hybrid anionic cluster at various concentrations and temperatures. It was found that both electrostatic interactions and cation-π interactions regulate the position of small countercations around single clusters. The dynamic geometry and the symmetry of the hybrid macroions are largely affected by the type of counterions, as shown by nuclear magnetic resonance (NMR) spectroscopy studies and all-atom molecular dynamics simulation. It is also shown that electrostatic interactions dominate over cation-π interactions in determining the locations of the counterions in the current system.
Adsorption of chlorinated organic contaminants (COCs) on carbon nanotubes (CNTs) has been gaining... more Adsorption of chlorinated organic contaminants (COCs) on carbon nanotubes (CNTs) has been gaining ground as a remedial platform for groundwater treatment. Applications depend on our mechanistic understanding of COC adsorption on CNTs. This paper lays out the nature of competing interactions at play in hybrid, membrane, and pure CNT based systems and presents results with the perspective of existing gaps in design strategies. First, current remediation approaches to trichloroethylene (TCE), the most ubiquitous of the COCs, is presented along with examination of forces contributing to adsorption of analogous contaminants at the molecular level. Second, we present results on TCE adsorption and remediation on pure and hybrid CNT systems with a stress on the specific nature of substrate and molecular architecture that would contribute to competitive adsorption. The delineation of intermolecular interactions that contribute to efficient remediation is needed for custom, scalable field design of purification systems for a wide range of contaminants.
Coarse-grained simulation approach is applied to provide a general understanding of various solub... more Coarse-grained simulation approach is applied to provide a general understanding of various soluble, hydrophilic macroionic solutions, especially the strong attractions among the like-charged soluble macroions and the consequent spontaneous, reversible formation of blackberry structures with tunable sizes. This model captures essential molecular details of the macroions and their interactions in polar solvents. Results using this model provide consistent conclusions to the experimental observations, from the nature of the attractive force among macroions (counterion-mediated attraction), to the blackberry formation mechanism. The conclusions can be applied to various macroionic solutions from inorganic molecular clusters to dendrimers and biomacromolecules.
ABSTRACT Anti-perovskite manganese nitrides Mn3Cu0.6AgxSn0.4−xN (x = 0–0.3) were synthesized by m... more ABSTRACT Anti-perovskite manganese nitrides Mn3Cu0.6AgxSn0.4−xN (x = 0–0.3) were synthesized by mechanical ball milling followed by solid state sintering. Their negative thermal expansion (NTE) coefficient and electrical resistivity were investigated in the temperature range of 80–300 K. It is found that the transition temperature of NTE gradually moves toward lower temperature and the NTE operation-temperature window (ΔT) becomes narrower with increasing Ag content within the testing temperature ranges. Interestingly, though the electrical resistivity of the samples shows a metallic behavior, the variation of electrical resistivity appears to be nearly independent of temperature above the transition temperature of NTE. The present discovery highlights the potential application of NTE materials in cryogenic engineering.
ABSTRACT In the present work, oil-field wastewater purification through superconducting magnetic ... more ABSTRACT In the present work, oil-field wastewater purification through superconducting magnetic separation technique using a novel magnetic nanoparticle was investigated. The magnetic nanoparticle, which has a multi-shell structure with ferroferric oxide as core, dense nonporous silica as inter layer and mesoporous silica as outer layer, was synthesized by co-precipitation method. To functionalize the magnetic nanoparticle, plasma polymerization technique was adopted and poly methyl acrylate (PMA) was formed on the surface of the nanoparticle. The multi-shell structure of the nanoparticle was confirmed by transmission electron microscope (TEM) and the characteristic is measurable by FTIR. It is found that most of the pollutants (85% by turbidity or 84% by COD value) in the oil-field wastewater are removed through the superconducting magnetic separation technique using this novel magnetic nanoparticle.
Various soluble hydrophilic macroions can self-assemble into hollow, spherical, monolayered supra... more Various soluble hydrophilic macroions can self-assemble into hollow, spherical, monolayered supramolecular "blackberry"-type structures, despite their like-charged nature. However, how the 3-D symmetrical macroions prefer to form 2-D monolayers in bulk solution, especially for the highly symmetrical "Keplerate" polyoxometalates and functionalized C macroions has been a mystery. Through molecular dynamics simulations, using a model specifically designed for macroions in solution, the mechanism of this intriguing symmetry-breaking process is found to be related to the apparently asymmetric charge distribution on the surface of macroions in the equatorial belt area (the area which can be effectively involved in the counterion-mediated attraction). As a result, the electric field lines around macroions during the self-assembly process clearly show that the symmetry-breaking happens at the dimer level effectively defining the plane of the self-assembly. These findings...
New experiments show that tensile stress vanishes shortly after preyield deformation of polymer g... more New experiments show that tensile stress vanishes shortly after preyield deformation of polymer glasses while tensile stress after postyield deformation stays high and relaxes on much longer time scales, thus hinting at a specific molecular origin of stress in ductile cold drawing: chain tension rather than intersegmental interactions. Molecular dynamics simulation based on a coarse-grained model for polystyrene confirms the conclusion that the chain network plays an essential role, causing the glassy state to yield and to respond with a high level of intrachain retractive stress. This identification sheds light on the future development regarding an improved theoretical account for molecular mechanics of polymer glasses and the molecular design of stronger polymeric materials to enhance their mechanical performance.
Angewandte Chemie (International ed. in English), Mar 15, 2017
We report herein an interesting dynamic translocation process of countercations around one polyox... more We report herein an interesting dynamic translocation process of countercations around one polyoxometalate(POM)-organic hybrid anionic cluster at various concentrations and temperatures. It was found that both electrostatic interactions and cation-π interactions regulate the position of small countercations around single clusters. The dynamic geometry and the symmetry of the hybrid macroions are largely affected by the type of counterions, as shown by nuclear magnetic resonance (NMR) spectroscopy studies and all-atom molecular dynamics simulation. It is also shown that electrostatic interactions dominate over cation-π interactions in determining the locations of the counterions in the current system.
Adsorption of chlorinated organic contaminants (COCs) on carbon nanotubes (CNTs) has been gaining... more Adsorption of chlorinated organic contaminants (COCs) on carbon nanotubes (CNTs) has been gaining ground as a remedial platform for groundwater treatment. Applications depend on our mechanistic understanding of COC adsorption on CNTs. This paper lays out the nature of competing interactions at play in hybrid, membrane, and pure CNT based systems and presents results with the perspective of existing gaps in design strategies. First, current remediation approaches to trichloroethylene (TCE), the most ubiquitous of the COCs, is presented along with examination of forces contributing to adsorption of analogous contaminants at the molecular level. Second, we present results on TCE adsorption and remediation on pure and hybrid CNT systems with a stress on the specific nature of substrate and molecular architecture that would contribute to competitive adsorption. The delineation of intermolecular interactions that contribute to efficient remediation is needed for custom, scalable field design of purification systems for a wide range of contaminants.
Coarse-grained simulation approach is applied to provide a general understanding of various solub... more Coarse-grained simulation approach is applied to provide a general understanding of various soluble, hydrophilic macroionic solutions, especially the strong attractions among the like-charged soluble macroions and the consequent spontaneous, reversible formation of blackberry structures with tunable sizes. This model captures essential molecular details of the macroions and their interactions in polar solvents. Results using this model provide consistent conclusions to the experimental observations, from the nature of the attractive force among macroions (counterion-mediated attraction), to the blackberry formation mechanism. The conclusions can be applied to various macroionic solutions from inorganic molecular clusters to dendrimers and biomacromolecules.
ABSTRACT Anti-perovskite manganese nitrides Mn3Cu0.6AgxSn0.4−xN (x = 0–0.3) were synthesized by m... more ABSTRACT Anti-perovskite manganese nitrides Mn3Cu0.6AgxSn0.4−xN (x = 0–0.3) were synthesized by mechanical ball milling followed by solid state sintering. Their negative thermal expansion (NTE) coefficient and electrical resistivity were investigated in the temperature range of 80–300 K. It is found that the transition temperature of NTE gradually moves toward lower temperature and the NTE operation-temperature window (ΔT) becomes narrower with increasing Ag content within the testing temperature ranges. Interestingly, though the electrical resistivity of the samples shows a metallic behavior, the variation of electrical resistivity appears to be nearly independent of temperature above the transition temperature of NTE. The present discovery highlights the potential application of NTE materials in cryogenic engineering.
ABSTRACT In the present work, oil-field wastewater purification through superconducting magnetic ... more ABSTRACT In the present work, oil-field wastewater purification through superconducting magnetic separation technique using a novel magnetic nanoparticle was investigated. The magnetic nanoparticle, which has a multi-shell structure with ferroferric oxide as core, dense nonporous silica as inter layer and mesoporous silica as outer layer, was synthesized by co-precipitation method. To functionalize the magnetic nanoparticle, plasma polymerization technique was adopted and poly methyl acrylate (PMA) was formed on the surface of the nanoparticle. The multi-shell structure of the nanoparticle was confirmed by transmission electron microscope (TEM) and the characteristic is measurable by FTIR. It is found that most of the pollutants (85% by turbidity or 84% by COD value) in the oil-field wastewater are removed through the superconducting magnetic separation technique using this novel magnetic nanoparticle.
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