Organic ionic plastic crystals (OIPCs) are the crystals of electrolytes with a long-range translational order. The rotational modes of ions in OIPCs are, however, activated even in solid phases such ...that the diffusion of dopants such as lithium ions may be facilitated. OIPCs have been, therefore, considered as good candidates for solid electrolytes. Recent experiments and theoretical studies have suggested that both the translational and the rotational diffusion of ions are quite heterogeneous: the diffusion of some ions are quite fast while other ions of the same kind hardly diffuse, either rotationally or translationally. Such dynamic heterogeneity would be a key to the transport mechanism of dopants in solid state electrolytes. In this work, we investigate the effects of defects on the dynamic heterogeneity of OIPCs. We perform atomistic molecular dynamics simulation of 1,3-dimethylimidazolium hexafluorophosphate (MMIMPF
6
) with a pair of cation and anion vacancies. At low temperature, vacancies undergo hopping motions toward each other and form a charge-neutral cluster. At high temperature, two vacancies act like a loosely bonded molecule and diffuse together
via
hopping motions. We find that the translational diffusion of ions is correlated strongly with the vacancy diffusion and becomes heterogeneous when the vacancies hop. The rotation of ions also becomes active when the ions are close to vacancies such that the rotational dynamic heterogeneity strengthens.
The presence of vacancies induces the translational and rotational dynamic heterogeneity of ions in the organic ionic plastic crystal.
Organic ionic plastic crystals (OIPCs) consist of molecular ions of which interactions are strong enough to maintain crystalline order but are weak enough to allow the rotations of the molecular ions ...at sufficiently high temperatures. When defects such as Schottky vacancies and grain boundaries are introduced into OIPCs, the defects facilitate the transport of dopants such as Li
+
ions, for which OIPCs are considered as strong candidates for solid electrolytes. The transport mechanism of dopant ions in OIPCs with defects, however, remains elusive at a molecular level partly because it is hard in experiments to track the dopant ions and control the types of defects systematically. In this work, we perform molecular dynamics simulations for 1,3-dimethylimidazolium hexafluorophosphate (MMIMPF
6
) OIPCs with Li
+
ions doped and show that the transport mechanism of Li
+
ions depends on the types and concentrations of defects. A high concentration of Schottky vacancies enhance the overall ion conduction, but decrease the transference number. The transference numbers of Li
+
ions in MMIMPF
6
with grain boundaries are similar to that in MMIMPF
6
with 0.78 mol% point vacancies. We also find that the transport of ions in OIPCs is strongly heterogeneous and the time scales of the dynamic heterogeneity of the ions are sensitive to the types of defects.
Defects such as grain boundaries alter the structure of ions and cause the non-Gaussian heterogenous dynamics of ions in OIPCs.
Various dopant alkali ions have been introduced into organic ionic plastic crystals (OIPCs) in order to design solid electrolytes with the desired thermal stability and ionic conductivity. We ...performed extensive molecular dynamics simulations to investigate at the molecular level how dopant alkali ions affect the rotational and the translational diffusion of ions and the thermal stability of OIPCs. We introduced lithium (Li
+
), sodium (Na
+
), and potassium (K
+
) ions as dopants into 1-methyl-3-methylimidazolium hexafluorophosphate (MMIMPF
6
) OIPCs at the molecular level. We found that as smaller alkali ions are doped, larger domains of the crystals are disrupted. This makes it harder for OIPCs doped with smaller alkali ions to maintain their crystal structure such that the melting temperature of OIPCs decreases and phase transitions between rotator phases change. The size of dopant alkali ions also affects the rotational diffusion of matrix ions of MMIM
+
and PF
6
−
: the rotational diffusion of matrix ions near Li
+
ions becomes more heterogeneous and facilitated than those near other kinds of alkali ions. We also find that alkali ions of different kinds diffuse translationally in OIPCs
via
different transport mechanisms: while the Li
+
ion undergoes continuous (anion-associated) diffusion through an amorphous region, the K
+
ion hops between neighbor lattice sites. To investigate the effects of the relative size between matrix cations and dopant ions on translational diffusions, we also simulate OIPCs with longer alkyl chains such as 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF
6
) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF
6
) crystals. We find that as the size of imidazolium cations increases, the hopping diffusion of the K
+
ion becomes suppressed and the K
+
ion is more likely to diffuse through amorphous domains.
The type of alkali ion dopant can alter the thermal stability and transport mechanisms of the organic plastic crystals (OIPCs).
The derivation of human embryonic stem cells (hESCs) by somatic cell nuclear transfer (SCNT) has prompted a re‐emerging interest in using such cells for therapeutic cloning. Despite recent ...advancements in derivation protocols, the functional potential of CHA‐NT4 derived cells is yet to be elucidated. For this reason, this study sought to differentiate CHA‐NT4 cells toward an endothelial lineage in order to evaluate in vitro and in vivo functionality. To initial differentiation, embryoid body formation of CHA‐NT4 was mediated by concave microwell system which was optimized for hESC‐endothelial cell (EC) differentiation. The isolated CD31+ cells exhibited hallmark endothelial characteristics in terms of morphology, tubule formation, and ac‐LDL uptake. Furthermore, CHA‐NT4‐derived EC (human nuclear transfer hNT‐ESC‐EC) transplantation in hind limb ischemic mice rescued the hind limb and restored blood perfusion. These findings suggest that hNT‐ESC‐EC are functionally equivalent to hESC‐ECs, warranting further study of CHA‐NT4 derivatives in comparison to other well established pluripotent stem cell lines. This revival of human SCNT‐ESC research may lead to interesting insights into cellular behavior in relation to donor profile, mitochondrial DNA, and oocyte quality. Stem Cells 2019;37:623–630
NT‐ESC derived ECs through a concave microwell system demonstrates functional potential regarding the restoration of blood perfusion to an ischemic limb through angiogenic factors.
The time-temperature superposition (TTS) principle, employed extensively for the analysis of polymer dynamics, is based on the assumption that the different normal modes of polymer chains would ...experience identical temperature dependence. We aim to test the critical assumption for TTS principle by investigating poly(ethylene oxide) (PEO) melts, which have been considered excellent solid polyelectrolytes. In this work, we perform all-atom molecular dynamics simulations up to 300 ns at a range of temperatures for PEO melts. We find from our simulations that the conformations of strands of PEO chains in melts show ideal chain statistics when the strand consists of at least 10 monomers. At the temperature range of T= 400 to 300 K, the mean-square displacements (⟨Δr2(t)⟩) of the centers of mass of chains enter the Fickian regime, i.e., ⟨Δr2(t)⟩∼t1. On the other hand, ⟨Δr2(t)⟩ of the monomers of the chains scales as ⟨Δr2(t)⟩∼t1/2 at intermediate time scales as expected for the Rouse model. We investigate various relaxation modes of the polymer chains and their relaxation times (τn), by calculating for each strand of
monomers. Interestingly, different normal modes of the PEO chains experience identical temperature dependence, thus indicating that the TTS principle would hold for the given temperature range.
Organic ionic plastic crystals (OIPCs) are a unique class of materials that undergo orientational and conformational motions while maintaining a long-range ordered lattice structure. OIPCs have ...attracted attention because the rotational motions were known to accelerate the diffusion of mobile ions such as lithium ions. However, only a small number of combinations of cations and anions lead to OIPCs because the rotational motion may be restricted by both the molecular structure and the crystal class. In this work, we perform molecular dynamics simulations to study the effects of the molecular structure and the crystal class on the rotational motion and the phase transitions. We investigate four imidazolium-based ionic crystals: (1) 1-methyl-3-methylimidazolium hexafluorophosphate (MMIMPF6), (2) 1-methyl-3-methylimidazolium chloride (MMIMCl), (3) monoclinic 1-butyl-3-methylimidazolium chloride (BMIMCl), and (4) orthorhombic BMIMCl ionic crystals. We construct initial configurations of OIPCs by employing experimental crystalline structures. Then, we increase the temperature gradually and monitor the density and the radial distribution functions. We estimate the rotational van Hove correlation functions and find that molecules in plastic crystal phases undergo rotational hopping motions and OIPCs exhibit rotational dynamic heterogeneity significantly. The structure of anions and cations affect the phase transition of OIPCs. And the crystal class is also critical to the phase transition of OIPCs because the rotational motion of ions depends on the crystal class.
The shape of a viral capsid affects the equilibrium conformation of DNA inside the capsid: the equilibrium DNA conformation inside a spherical capsid is a concentric spool while the equilibrium ...conformation inside an elongated capsid is a twisted toroid. The conformation of DNA, jammed inside the capsid due to high internal pressure, influences the ejection kinetics of the DNA from the capsid. Therefore, one would expect that the DNA ejection kinetics would be subject to the shape of the viral capsid. The effects of the capsid shape on the ejection, however, remain elusive partly due to a plethora of viral capsid shapes. In this work, we perform Langevin dynamics simulations for the ejection of a polymer chain from three different types of viral capsids: (1) spherical, (2) cubic, and (3) cuboid capsids. We find that the ejection rate of the polymer chain from the spherical capsid is much faster than that from either cubic or cuboid capsids. The polymer chain in the spherical capsid may undergo collective rotational relaxation more readily such that the polymer chain becomes more mobile inside the spherical capsid, which enhances the ejection kinetics. On the other hand, a threading motion is dominant inside cubic and cuboid capsids. We also find that the effects of the collective rotational motion become more significant for a more rigid chain inside a capsid.
Polymer chains in various biological and material processes are subject to repetitive cycles of packaging and ejection via small confinements. For example, a DNA is packaged into and ejected from a ...viral capsid during the virus replication. The ejection of the chain is often considered independent of how the chain was packaged in the first place. In this study, we perform Langevin dynamics simulations and investigate the packaging and ejection process of a semiflexible chain in a cubic confinement. We show that the ejection process should depend significantly on how the chain was packaged and that the ejection process can be categorized into three regimes: (1) knot dominant, (2) nonequilibrium conformation dominant, and (3) intermediate regimes. In case a polymer chain was packaged sufficiently slowly, the chain forms a complex knot easily such that the ejection slows down (the knot dominant regime). When the packaging occurred quickly, the knots hardly form, but the polymer chain is jammed in nonequilibrium conformational states, which slows down the ejection (nonequilibrium dominant regime). For a moderate packaging rate, the polymer chain may relax its conformation readily with a low chance of knot formation, thus leading to fast ejection (the intermediate regime).
High-quality indium–gallium–zinc oxide (IGZO) films synthesized by atomic layer deposition (ALD) using a single cocktail precursor based on a liquid-delivery system are demonstrated for the first ...time. A bottom-gate-top-contact thin-film transistor (TFT) consisting of an ALD-derived IGZO channel exhibited outstanding device performance, including a high linear field-effect mobility (∼20 cm 2 V −1 s −1 ), a substantial on/off ratio (∼5 × 10 9 ), and a low subthreshold swing (∼0.07 V dec −1 ) at an operating voltage of 5 V. High reliability and reproducibility of the proposed ALD-based IGZO TFT are confirmed from the statistics of device key parameters. The operational stability of the IGZO TFT subjected to electrical bias stresses for 20 000s is investigated, which is attributed to the oxygen-related defect states of the ALD-derived IGZO film and the field-induced interaction with oxygen on the surface. In addition, full recovery of V th without additional processes was achieved, indicating that the instability mechanism can be explained by shallow charge trapping at the interface. A simple and effective method of oxygen annealing is induced to improve the operational stability of the IGZO TFT by suppressing the oxygen-related shallow trap states. Finally, an enhancement-load-type n-channel metal-oxide semiconductor inverter consisting of two IGZO TFTs proposed in this study is developed.
We have measured the high-resolution vibrational spectra of a thietane (trimethylene sulfide) cation in the gas phase by employing the vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) ...spectroscopic technique. Peaks in the low-frequency region of the observed MATI spectrum of thietane originate from a progression of the ring-puckering vibrational mode (typical in small heterocyclic molecules), which is successfully reproduced by quantum-chemical calculations with 1D symmetric double-well potentials along the ring puckering coordinates on both the S0 and D0 states, the ground electronic states of neutral and cation of thietane, respectively. The values of the interconversion barrier and the ring-puckering angle on the S0 state, the parameters used for the quantum-chemical calculations, were assumed to be 274 cm–1 and 26°. The barrier and the angle on the D0 state, however, are found to be 48.0 cm–1 and 18.2°, respectively, where such small barrier height and puckering angle for the cation suggest that the conformation of thietane cation on the D0 state should be more planar than that of the thietane neutral.
PDF
