The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
William J Koros - One of the best experts on this subject based on the ideXlab platform.
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carbon dioxide sorption and transport in amorphous poly ethylene furanoate
Macromolecules, 2015Co-Authors: Steven K Burgess, Robert M Kriegel, William J KorosAbstract:Transport properties of carbon dioxide in amorphous poly(ethylene furanoate) (PEF) were investigated using complementary pressure-decay sorption and permeation techniques. Detailed measurements for PEF at 35 °C indicate a significant, surprisingly large reduction in carbon dioxide permeability of 19× at 1 atm compared to poly(ethylene terephthalate) (PET), despite both an increase in free volume and carbon dioxide solubility of 1.6× for PEF vs PET. The solubility increase for PEF, which originates from greater interaction between carbon dioxide and the polar furan moiety, is offset by a substantial reduction in diffusivity of 31× compared to PET. Such diffusion reduction for PEF, which is 3× greater than the 9.7× reduction in oxygen diffusivity compared to PET, is thought to originate from a hindrance of polymer Ring-Flipping motions compared to PET. A possible mechanism for the surprising barrier improvement for carbon dioxide in PEF vs PET is explained herein along with a detailed comparison to oxygen a...
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oxygen sorption and transport in amorphous poly ethylene furanoate
Polymer, 2014Co-Authors: Steven K Burgess, Robert M Kriegel, Oguz Karvan, Justin R Johnson, William J KorosAbstract:Abstract Oxygen transport in amorphous poly(ethylene furanoate) (PEF) was studied at various temperatures using complementary permeation and pressure-decay sorption techniques. A significant reduction in oxygen permeability of ∼11× was observed at 35 °C for PEF compared to poly(ethylene terephthalate) (PET), and is attributed primarily to reduction in chain segment mobility for PEF resulting from a hindrance of furan Ring Flipping. A custom-built high accuracy sorption system allowed determination of temperature-dependent so-called dual-mode parameters that have not been reported for oxygen in any polyester. Energetic parameters, i.e. the enthalpy of sorption and activation energies of diffusion and permeation, were measured for oxygen in PEF and discussed in the context of PET and related polyesters. The current work presents the first detailed study of penetrant transport in PEF, which demonstrates the impressive performance enhancements of PEF compared to PET.
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chain mobility thermal and mechanical properties of poly ethylene furanoate compared to poly ethylene terephthalate
Macromolecules, 2014Co-Authors: Steven K Burgess, Johannes Leisen, Brian Kraftschik, Christopher R Mubarak, Robert M Kriegel, William J KorosAbstract:Poly(ethylene furanoate) (PEF), the furan-derived analogue to poly(ethylene terephthalate) (PET), can provide a fully biosourced alternative to PET with greatly improved barrier properties and attractive thermal and mechanical properties. The improved barrier for PEF compared to PET is unexpected due to the higher free volume of PEF vs PET. Segmental motions related to penetrant diffusion in both polyesters were studied using dynamic mechanical analysis, 13C–CP/MAS solid-state NMR variable contact-time experiments, and centerband-only detection of exchange (CODEX) measurements. Unlike the active phenyl Ring-Flipping mechanism in PET, furan Ring-Flipping is greatly suppressed, thereby reducing β relaxation motions and diffusion in PEF due to the energy penalty associated with the nonlinear axis of Ring rotation and Ring polarity. Preliminary work also shows similar oxygen solubilities for PEF and PET, thereby proving that the drastic permeability reduction results from a decrease in diffusion coefficient c...
Johannes Kastner - One of the best experts on this subject based on the ideXlab platform.
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comment on computational evidence for sulfur atom tunneling in the Ring Flipping reaction of s4n4
Chemical Physics Letters, 2020Co-Authors: Ashim Nandi, Sebastian Kozuch, Johannes KastnerAbstract:Abstract In a recent article (Chem. Phys. Lett. 749 (2020), 137440), Kumar and Mallick predict by computations that a sulfur atom tunneling mechanism leads to a Ring Flipping reaction of S4N4 below 70 K. Herein, on the basis of their tunneling computations, it is shown that the sulfur atom tunneling is not viable, and therefore impossible to be probed experimentally. Based on this, we discuss the prerequisites for a chemical reaction to be driven by heavy atom tunneling.
Mircea Dincă - One of the best experts on this subject based on the ideXlab platform.
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conformational locking by design relating strain energy with luminescence and stability in rigid metal organic frameworks
Journal of the American Chemical Society, 2012Co-Authors: Natalia B Shustova, Anthony F Cozzolino, Mircea DincăAbstract:Minimization of the torsional barrier for phenyl Ring Flipping in a metal–organic framework (MOF) based on the new ethynyl-extended octacarboxylate ligand H8TDPEPE leads to a fluorescent material with a near-dark state. Immobilization of the ligand in the rigid structure also unexpectedly causes significant strain. We used DFT calculations to estimate the ligand strain energies in our and all other topologically related materials and correlated these with empirical structural descriptors to derive general rules for trapping molecules in high-energy conformations within MOFs. These studies portend possible applications of MOFs for studying fundamental concepts related to conformational locking and its effects on molecular reactivity and chromophore photophysics.
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phenyl Ring dynamics in a tetraphenylethylene bridged metal organic framework implications for the mechanism of aggregation induced emission
Journal of the American Chemical Society, 2012Co-Authors: Natalia B Shustova, Anthony F Cozzolino, Tachung Ong, Vladimir K Michaelis, Robert G Griffin, Mircea DincăAbstract:Molecules that exhibit emission in the solid state, especially those known as aggregation-induced emission (AIE) chromophores, have found applications in areas as varied as light-emitting diodes and biological sensors. Despite numerous studies, the mechanism of fluorescence quenching in AIE chromophores is still not completely understood. To this end, much interest has focused on understanding the low-frequency vibrational dynamics of prototypical systems, such as tetraphenylethylene (TPE), in the hope that such studies would provide more general principles toward the design of new sensors and electronic materials. We hereby show that a perdeuterated TPE-based metal–organic framework (MOF) serves as an excellent platform for studying the low-energy vibrational modes of AIE-type chromophores. In particular, we use solid-state 2H and 13C NMR experiments to investigate the phenyl Ring dynamics of TPE cores that are coordinatively trapped inside a MOF and find a phenyl Ring Flipping energy barrier of 43(6) kJ...
Pradeep Kumar - One of the best experts on this subject based on the ideXlab platform.
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computational evidence for sulfur atom tunneling in the Ring Flipping reaction of s4n4
Chemical Physics Letters, 2020Co-Authors: Subhasish Mallick, Pradeep KumarAbstract:Abstract It has been shown by means of ab initio calculations and kinetic studies that the sulfur atom tunneling can play a crucial role in the Ring Flipping reaction of S4N4, which is a main precursor of the superconducting material polythiazyl. The investigations indicate that, below 70 K, the reaction predominantly occurs via tunneling, and at 150 K temperature, the tunneling increases the reaction rate by approximately two times.
Steven K Burgess - One of the best experts on this subject based on the ideXlab platform.
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carbon dioxide sorption and transport in amorphous poly ethylene furanoate
Macromolecules, 2015Co-Authors: Steven K Burgess, Robert M Kriegel, William J KorosAbstract:Transport properties of carbon dioxide in amorphous poly(ethylene furanoate) (PEF) were investigated using complementary pressure-decay sorption and permeation techniques. Detailed measurements for PEF at 35 °C indicate a significant, surprisingly large reduction in carbon dioxide permeability of 19× at 1 atm compared to poly(ethylene terephthalate) (PET), despite both an increase in free volume and carbon dioxide solubility of 1.6× for PEF vs PET. The solubility increase for PEF, which originates from greater interaction between carbon dioxide and the polar furan moiety, is offset by a substantial reduction in diffusivity of 31× compared to PET. Such diffusion reduction for PEF, which is 3× greater than the 9.7× reduction in oxygen diffusivity compared to PET, is thought to originate from a hindrance of polymer Ring-Flipping motions compared to PET. A possible mechanism for the surprising barrier improvement for carbon dioxide in PEF vs PET is explained herein along with a detailed comparison to oxygen a...
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oxygen sorption and transport in amorphous poly ethylene furanoate
Polymer, 2014Co-Authors: Steven K Burgess, Robert M Kriegel, Oguz Karvan, Justin R Johnson, William J KorosAbstract:Abstract Oxygen transport in amorphous poly(ethylene furanoate) (PEF) was studied at various temperatures using complementary permeation and pressure-decay sorption techniques. A significant reduction in oxygen permeability of ∼11× was observed at 35 °C for PEF compared to poly(ethylene terephthalate) (PET), and is attributed primarily to reduction in chain segment mobility for PEF resulting from a hindrance of furan Ring Flipping. A custom-built high accuracy sorption system allowed determination of temperature-dependent so-called dual-mode parameters that have not been reported for oxygen in any polyester. Energetic parameters, i.e. the enthalpy of sorption and activation energies of diffusion and permeation, were measured for oxygen in PEF and discussed in the context of PET and related polyesters. The current work presents the first detailed study of penetrant transport in PEF, which demonstrates the impressive performance enhancements of PEF compared to PET.
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chain mobility thermal and mechanical properties of poly ethylene furanoate compared to poly ethylene terephthalate
Macromolecules, 2014Co-Authors: Steven K Burgess, Johannes Leisen, Brian Kraftschik, Christopher R Mubarak, Robert M Kriegel, William J KorosAbstract:Poly(ethylene furanoate) (PEF), the furan-derived analogue to poly(ethylene terephthalate) (PET), can provide a fully biosourced alternative to PET with greatly improved barrier properties and attractive thermal and mechanical properties. The improved barrier for PEF compared to PET is unexpected due to the higher free volume of PEF vs PET. Segmental motions related to penetrant diffusion in both polyesters were studied using dynamic mechanical analysis, 13C–CP/MAS solid-state NMR variable contact-time experiments, and centerband-only detection of exchange (CODEX) measurements. Unlike the active phenyl Ring-Flipping mechanism in PET, furan Ring-Flipping is greatly suppressed, thereby reducing β relaxation motions and diffusion in PEF due to the energy penalty associated with the nonlinear axis of Ring rotation and Ring polarity. Preliminary work also shows similar oxygen solubilities for PEF and PET, thereby proving that the drastic permeability reduction results from a decrease in diffusion coefficient c...
