The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform
Toshikazu Miyoshi - One of the best experts on this subject based on the ideXlab platform.
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chain trajectory chain packing and molecular dynamics of semicrystalline polymers as studied by solid state nmr
Polymers, 2018Co-Authors: Shijun Wang, Youlee Hong, Shichen Yuan, Wei Chen, Wenxuan Zhou, Kun Wang, Xu Min, Takashi Konishi, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, 13C⁻13C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (Cf) Structure and packing Structure of 13C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.
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Molecular Structural Basis for Stereocomplex Formation of Polylactide Enantiomers in Dilute Solution
ACS Macro Letters, 2015Co-Authors: Wei Chen, Youlee Hong, Shijun Wang, Wei Zhang, Toshikazu MiyoshiAbstract:Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) alternatively pack with each other and form stereocomplex crystals (SCs). The crystal habits of SCs formed in the dilute solution highly depend on the molecular weight (⟨Mw⟩). In this study, we investigated chain-folding (Cf) Structure for 13C labeled PLLA (l-PLLA) chains in SCs with PDLAs that have either high or low ⟨Mw⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨n⟩ for the l-PLLA chains drastically change depending on ⟨Mw⟩s of the counter PDLA chains in the SCs. It was concluded that the Cf Structures of l-PLLA depending on ⟨Mw⟩s of PDLA determine the crystal habits of SCs.
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Chain Trajectory and Crystallization Mechanism of a Semicrystalline Polymer in Melt- and Solution-Grown Crystals As Studied Using 13C–13C Double-Quantum NMR
Macromolecules, 2015Co-Authors: Youlee Hong, Tadanori Koga, Toshikazu MiyoshiAbstract:The re-entrance sites, successive chain-folding number ⟨n⟩, and chain-folding fraction ⟨F⟩ of the chain-folding (Cf) Structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) with an weight-averaged molecular weight (⟨Mw⟩ = 37 K g/mol) in solution- and melt-grown crystals as a function of crystallization temperature (Tc) were determined using solid-state (SS) NMR. The solution- and melt-grown crystals possessed adjacent re-entry Structures between the right- and left-handed stems along the (100) and (010) planes, which were invariant as a function of Tc. The adjacent re-entry Structures in the former exhibited long-range order (⟨n⟩ ≥ 8) compared with that in the latter (⟨n⟩ ≥ 1.7–2). These results indicated that the concentration and entanglement of polymers play significant roles in the Cf process and structural formation during the initial stage of crystallization, whereas kinetics does not. Transmission electron microscopy (TEM) revealed well-defined hexagonal and circular crystals grown from the so...
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elucidation of the chain folding Structure of a semicrystalline polymer in single crystals by solid state nmr
ACS Macro Letters, 2014Co-Authors: Youlee Hong, Toshikazu MiyoshiAbstract:Despite tremendous efforts over the last half-century to elucidate the chain-folding (Cf) Structure of semicrystalline polymers, the re-entrance sites of folded chains, the successive Cf number n, and the adjacent re-entry fraction F have not been well characterized due to experimental limitations. In this report, 13C–13C double-quantum (DQ) NMR was used to determine for the first time the detailed Cf Structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) in solution-grown crystals blended with nonlabeled iPB1 across a wide range of crystallization temperatures (Tcs). Comparison of the results of DQ experiments and spin dynamics simulations demonstrated that the majority of individual chains possess completely adjacent re-entry Structures at both Tc = 60 and ∼0 °C, as well as indicated that a low polymer concentration, not kinetics, leads to cluster formations of single molecules in dilute solution. The changes in crystal habits from hexagonal shapes at Tc = 60 °C to rounded shapes at ∼0 °C (kinetic...
Youlee Hong - One of the best experts on this subject based on the ideXlab platform.
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chain trajectory chain packing and molecular dynamics of semicrystalline polymers as studied by solid state nmr
Polymers, 2018Co-Authors: Shijun Wang, Youlee Hong, Shichen Yuan, Wei Chen, Wenxuan Zhou, Kun Wang, Xu Min, Takashi Konishi, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, 13C⁻13C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (Cf) Structure and packing Structure of 13C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.
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Molecular Structural Basis for Stereocomplex Formation of Polylactide Enantiomers in Dilute Solution
ACS Macro Letters, 2015Co-Authors: Wei Chen, Youlee Hong, Shijun Wang, Wei Zhang, Toshikazu MiyoshiAbstract:Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) alternatively pack with each other and form stereocomplex crystals (SCs). The crystal habits of SCs formed in the dilute solution highly depend on the molecular weight (⟨Mw⟩). In this study, we investigated chain-folding (Cf) Structure for 13C labeled PLLA (l-PLLA) chains in SCs with PDLAs that have either high or low ⟨Mw⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨n⟩ for the l-PLLA chains drastically change depending on ⟨Mw⟩s of the counter PDLA chains in the SCs. It was concluded that the Cf Structures of l-PLLA depending on ⟨Mw⟩s of PDLA determine the crystal habits of SCs.
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Chain Trajectory and Crystallization Mechanism of a Semicrystalline Polymer in Melt- and Solution-Grown Crystals As Studied Using 13C–13C Double-Quantum NMR
Macromolecules, 2015Co-Authors: Youlee Hong, Tadanori Koga, Toshikazu MiyoshiAbstract:The re-entrance sites, successive chain-folding number ⟨n⟩, and chain-folding fraction ⟨F⟩ of the chain-folding (Cf) Structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) with an weight-averaged molecular weight (⟨Mw⟩ = 37 K g/mol) in solution- and melt-grown crystals as a function of crystallization temperature (Tc) were determined using solid-state (SS) NMR. The solution- and melt-grown crystals possessed adjacent re-entry Structures between the right- and left-handed stems along the (100) and (010) planes, which were invariant as a function of Tc. The adjacent re-entry Structures in the former exhibited long-range order (⟨n⟩ ≥ 8) compared with that in the latter (⟨n⟩ ≥ 1.7–2). These results indicated that the concentration and entanglement of polymers play significant roles in the Cf process and structural formation during the initial stage of crystallization, whereas kinetics does not. Transmission electron microscopy (TEM) revealed well-defined hexagonal and circular crystals grown from the so...
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elucidation of the chain folding Structure of a semicrystalline polymer in single crystals by solid state nmr
ACS Macro Letters, 2014Co-Authors: Youlee Hong, Toshikazu MiyoshiAbstract:Despite tremendous efforts over the last half-century to elucidate the chain-folding (Cf) Structure of semicrystalline polymers, the re-entrance sites of folded chains, the successive Cf number n, and the adjacent re-entry fraction F have not been well characterized due to experimental limitations. In this report, 13C–13C double-quantum (DQ) NMR was used to determine for the first time the detailed Cf Structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) in solution-grown crystals blended with nonlabeled iPB1 across a wide range of crystallization temperatures (Tcs). Comparison of the results of DQ experiments and spin dynamics simulations demonstrated that the majority of individual chains possess completely adjacent re-entry Structures at both Tc = 60 and ∼0 °C, as well as indicated that a low polymer concentration, not kinetics, leads to cluster formations of single molecules in dilute solution. The changes in crystal habits from hexagonal shapes at Tc = 60 °C to rounded shapes at ∼0 °C (kinetic...
Shijun Wang - One of the best experts on this subject based on the ideXlab platform.
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chain trajectory chain packing and molecular dynamics of semicrystalline polymers as studied by solid state nmr
Polymers, 2018Co-Authors: Shijun Wang, Youlee Hong, Shichen Yuan, Wei Chen, Wenxuan Zhou, Kun Wang, Xu Min, Takashi Konishi, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, 13C⁻13C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (Cf) Structure and packing Structure of 13C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.
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Molecular Structural Basis for Stereocomplex Formation of Polylactide Enantiomers in Dilute Solution
ACS Macro Letters, 2015Co-Authors: Wei Chen, Youlee Hong, Shijun Wang, Wei Zhang, Toshikazu MiyoshiAbstract:Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) alternatively pack with each other and form stereocomplex crystals (SCs). The crystal habits of SCs formed in the dilute solution highly depend on the molecular weight (⟨Mw⟩). In this study, we investigated chain-folding (Cf) Structure for 13C labeled PLLA (l-PLLA) chains in SCs with PDLAs that have either high or low ⟨Mw⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨n⟩ for the l-PLLA chains drastically change depending on ⟨Mw⟩s of the counter PDLA chains in the SCs. It was concluded that the Cf Structures of l-PLLA depending on ⟨Mw⟩s of PDLA determine the crystal habits of SCs.
Wei Chen - One of the best experts on this subject based on the ideXlab platform.
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chain trajectory chain packing and molecular dynamics of semicrystalline polymers as studied by solid state nmr
Polymers, 2018Co-Authors: Shijun Wang, Youlee Hong, Shichen Yuan, Wei Chen, Wenxuan Zhou, Kun Wang, Xu Min, Takashi Konishi, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, 13C⁻13C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (Cf) Structure and packing Structure of 13C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.
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Molecular Structural Basis for Stereocomplex Formation of Polylactide Enantiomers in Dilute Solution
ACS Macro Letters, 2015Co-Authors: Wei Chen, Youlee Hong, Shijun Wang, Wei Zhang, Toshikazu MiyoshiAbstract:Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) alternatively pack with each other and form stereocomplex crystals (SCs). The crystal habits of SCs formed in the dilute solution highly depend on the molecular weight (⟨Mw⟩). In this study, we investigated chain-folding (Cf) Structure for 13C labeled PLLA (l-PLLA) chains in SCs with PDLAs that have either high or low ⟨Mw⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨n⟩ for the l-PLLA chains drastically change depending on ⟨Mw⟩s of the counter PDLA chains in the SCs. It was concluded that the Cf Structures of l-PLLA depending on ⟨Mw⟩s of PDLA determine the crystal habits of SCs.
Ming Liu - One of the best experts on this subject based on the ideXlab platform.
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Analysis on the Filament Structure Evolution in Reset Transition of Cu/HfO2/Pt RRAM Device
Nanoscale Research Letters, 2016Co-Authors: Meiyun Zhang, Hangbing Lv, Shibing Long, Jordi Suñé, Enrique Miranda, Yang Li, Qi Liu, Ming LiuAbstract:The resistive switching (RS) process of resistive random access memory (RRAM) is dynamically correlated with the evolution process of conductive path or conductive filament (Cf) during its breakdown (rupture) and recovery (reformation). In this study, a statistical evaluation method is developed to analyze the filament Structure evolution process in the reset operation of Cu/HfO2/Pt RRAM device. This method is based on a specific functional relationship between the Weibull slopes of reset parameters’ distributions and the Cf resistance (Ron). The Cf of the Cu/HfO2/Pt device is demonstrated to be ruptured abruptly, and the Cf Structure of the device has completely degraded in the reset point. Since no intermediate states are generated in the abrupt reset process, it is quite favorable for the reliable and stable one-bit operation in RRAM device. Finally, on the basis of the cell-based analytical thermal dissolution model, a Monte Carlo (MC) simulation is implemented to further verify the experimental results. This work provides inspiration for RRAM reliability and performance design to put RRAM into practical application.