Extended Structure Research Articles

Dimensionality and Molecular Packing Control of Covalent Organic Frameworks through Pendant Group Design.

Tuning the dimensions and molecular packing geometry of crystalline organic frameworks and polymers represents an important challenge for reticular chemistry. Here we show that for extended structures made of 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTTA) linked with methoxy group functionalized terephthalaldehyde aldehydes, simple substituents on the aldehyde linker can have profound structure directing effects due to noncovalent interactions. Specifically, reacting 2,3-dimethoxyterephthalaldehyde with PyTTA gives a 2D covalent organic framework with unique AA-inclined-AA stacking and bilayer pyrene motifs, whereas reacting 2,5-dimethoxyterephthalaldehyde with PyTTA gives a 1D crystalline polymer with AB stacking and isolated pyrene motifs. Both materials show high crystallinity, allowing for atomic resolution structure determination using three-dimensional electron diffraction, and the similarity of their fluorescence properties shows the electronic structures of pyrene-based extended structures mostly depends on the in-plane structures, which is supported by density functional theory calculations. These two pyrene-based extended structures also show different fluorescence responses to organic vapors due to different pore environments. The current work shows the potential of noncovalent interactions in the reticular design of functional organic materials.

Dual active sites of N-rich triptycene-based 2D conductive metal–organic framework with 3D extended structures in high-performance lithium-ion batteries

Two-dimensional conductive metal–organic frameworks (2D c-MOFs) have attracted much attention in energy storage due to their special conjugated structures and electronic properties. However, the insufficient exposure of the active site due to layer stacking and the non-redox-active ligand molecules are detrimental to the specific capacity. In this study, a nitrogen-rich triptycene-based 2D c-MOF (M−TH5) with vertical extension was synthesized for the first time as an anode material. The triptycene-based ligand structure confers a 3D extension of the MOF alleviating the stacking problem and allowing full exposure of its active site. Furthermore, M−TH5 has a dual redox center (TH5 and MO4 units containing N sites), which can provide additional lithium storage sites. Expectedly, Mn-TH5 compared to Co-TH5 exhibits higher initial capacity (486.3 mAh·g−1 at 100 mA·g−1) and excellent long-term cycling stability (capacity retention of 91.9 % at 500 mA·g−1 after 400 cycles). Experimentally and computationally, the flower-like morphology and the nitrogen-rich system with three-dimensional (3D) expansion have more exposed active sites to facilitate Li+/e- transport. This finding provides new opportunities to improve anode material properties by integrating multiple active centers into 2D c-MOF

Effect of spatially varying earthquake ground motions on seismic response of a railway viaduct considering multiple site configurations

Currently, it is admitted that extended structures are subjected to spatially varying earthquake ground motions. It has been recognized that the causes of this variability are time delay at each support of the structure, coherency loss effect caused by the propagation of seismic waves and local site effect. The spatial variation of local characteristics of the soil profile defines the site effect, which affects the amplitude and the frequency content of seismic ground motion. The main objective of this work is to provide comparative results and evaluate the variation of the dynamic response of a bridge adopting varying characteristics of soil foundation. Based on the density spectral method, an efficient simulation method of spatially varying earthquake ground motions is developed. The simulation of spatially variable seismic ground motions is performed for different locations on the ground surface with varying site conditions. According to of soil classification described in seismic codes, four different soil configurations were considered for generating sixty-four displacement time series. Several dynamics analyses of a bridge to three cases of spatially variable seismic ground motions, besides the uniform case, are made. The results of this study indicate that depending on soil configurations beneath each support, the seismic response may vary significantly.

Conversion of Carbon Dioxide into Molecular-based Porous Frameworks.

ConspectusThe conversion of carbon dioxide (CO2) to value-added functional materials is a major challenge in realizing a carbon-neutral society. Although CO2 is an attractive renewable carbon resource with high natural abundance, its chemical inertness has made the conversion of CO2 into materials with the desired structures and functionality difficult. Molecular-based porous materials, such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), are designable porous solids constructed from molecular-based building units. While MOF/COFs attract wide attention as functional porous materials, the synthetic methods to convert CO2 into MOF/COFs have been unexplored due to the lack of synthetic guidelines for converting CO2 into molecular-based building units.In this Account, we describe state-of-the-art studies on the conversion of CO2 into MOF/COFs. First, we outline the key design principles of CO2-derived molecular building units for the construction of porous structures. The appropriate design of reactivity and the positioning of bridging sites in CO2-derived molecular building units is essential for constructing CO2-derived MOF/COFs with desired structures and properties. The synthesis of CO2-derived MOF/COFs involves both the transformation of CO2 into building units and the formation of extended structures of the MOF/COFs. We categorized the synthetic methods into three types as follows: a one-step synthesis (Type-I); a one-pot synthesis without workup (Type-II); and a multistep synthesis which needs workup (Type-III).We demonstrate that borohydride can convert CO2 into formate and formylhydroborate that serve as a bridging linker for MOFs in the Type-I and Type-II synthesis, representing the first examples of CO2-derived MOFs. The electronegativity of coexisting metal ions determines the selective conversion of CO2 into formate and formylhydroborate. Formylhydroborate-based MOFs exhibit flexible pore sizes controlled by the pressure of CO2 during synthesis. In pursuit of highly porous structures, we present the Type-I synthesis of MOFs from CO2 via the in situ transformation of CO2 into carbamate linkers by amines. The direct conversion of diluted CO2 (400 ppm) in air into carbamate-based MOFs is also feasible. Coordination interactions stabilize the intrinsically labile carbamate in the MOF lattice. A recent study demonstrates that the Type-III synthesis using alkynylsilane precursors enables the synthesis of highly porous and stable carboxylate-based MOFs from CO2, which exhibit catalytic activity in CO2 conversion. We also extended the synthesis of MOFs from CO2 to COFs. The Type-III synthesis using a formamide monomer affords stable CO2-derived COFs showing proton conduction properties. The precise design of CO2-derived building units enables expansion of the structures and functionalities of CO2-derived MOF/COFs. Finally, we propose future challenges in this field: (i) expanding structural diversity through synthesis using external fields and (ii) exploring unique functionalities of CO2-derived MOF/COFs, such as carriers for CO2 capture and precursors for CO2 transformation. We anticipate that this Account will lay the foundation for exploring new chemistry of the conversion of CO2 into porous materials.

Development of linear bearing equipment for modal testing of low-frequency weakly damped spacecraft structures

This article presents the results of a study of the bearing capacity and dissipative properties of an aerostatic linear bearing developed at JSC RESHETNEV for modal testing of complex structures. When selecting equipment for modal testing, the main condition is the requirement to minimize the distortions introduced into the determined dynamic characteristics: frequencies of natural vibration modes, the vibration modes themselves, as well as modal masses and damping coefficients. In other words, all equipment used for ground-based modal testing should ideally have zero added mass, stiffness and friction. The main systems containing elements that create dissipative forces that affect the determination of damping coefficients are systems for weight compensation and vibration excitation on natural modes. The weight compensation system usually contains either elastic elements or a system of guides with rolling or sliding bearings. If the former bring additional rigidity and mass to the test object, the latter bring mass and friction (dry or viscous), which increases the error in determining the dynamic characteristics. The excitation of vibrations on natural modes, in most cases, is carried out by electrodynamic vibrators consisting of a magnetization coil (or permanent magnet) and a movable coil moving in a magnetic gap. The movable coil is oriented in the magnetic gap using a special system containing either elastic elements or a linear guide bearing. Vibrators with elastic coil suspension elements cannot be used for modal tests of extended structures with low rigidity. The problem of creating an ideal bearing to replace classic linear (sliding or roller) ones arose during preparation for modal tests of the wing of a solar battery of a spacecraft (SC). Aerostatic bearings (supports) have virtually zero friction and sufficient load-bearing capacity, in which compressed air acts as a lubricant, eliminating physical contacts of the interacting surfaces. To confirm the possibility of using aerostatic bearings in equipment for conducting modal tests of extended structures with low frequencies of natural oscillations, comparative tests of a roller and aerostatic bearing were carried out. During the tests, optimal air flow parameters (nozzle diameter, operating pressure and gap) were selected, which ensure the required load-bearing capacity for radial forces and torques (bending and torsion). A comparative assessment of dissipative properties was carried out when measuring the attenuation parameters of single-mass harmonic oscillators, which include aerostatic and roller linear bearings. With a nozzle diameter of 0.6 mm, a working gap of 40 μm and a bearing input pressure of 1.0 bar, the logarithmic decrement of oscillations of the harmonic oscillator with an aerostatic bearing was 0.084, which is more than 28 times lower than the logarithmic decrement of oscillations of an oscillator with a roller bearing. The conducted studies confirmed the possibility of using the developed aerostatic bearing in test systems used in modal tests of large-sized transformable spacecraft structures.

Experimental study on the thermal performance of a novel vapor chamber manufactured by 3D-printing technology

Vapor chamber holds great application potential in the field of heat dissipation for high-power electronic devices. This study developed a novel vapor chamber using 3D-printing technology to enhance heat dissipation for compact electronic devices. The vapor chamber was constructed from aluminum alloy with a structural dimension of 60×60×30mm3. In this work, the extended condensation structure of the vapor chamber was combined with an external cooling structure, resulting in a 729 % increase in the external heat dissipation area compared to the evaporation area in a limited space. Extensive experiments were conducted using deionized water as the working fluid under various cooling conditions and heat loads. The results showed that the vapor chamber was capable of maintaining a low thermal resistance at high power and high heat flux conditions, with a minimum thermal resistance of 0.087 °C/W when the heat load was 1000 W. At a cooling water flow rate of 0.1 L/s, the vapor chamber demonstrated the capacity to withstand a critical heat load of up to 1600 W, with the heat flux of 326 W/cm2. Compared to conventional vapor chambers, this novel vapor chamber is better able to achieve stable and efficient heat dissipation under high power and high heat flux conditions, especially in a limited space.

Insights into lipid-modified recognition of Apolipoprotein E3 to extra-cellular domain of TREM2 associated with Alzheimer’s disease

E3 genotype of apolipoprotein E (ApoE) and triggering receptor expressed on myeloid cells 2 (TREM2) are critical genetic risk factors for late-onset Alzheimer’s diseases (AD) that influences the formation of plaques and neurofibrillary tangles associated with AD pathogenesis. In addition, variation in genetic association of ApoE and TREM2 in presence of lipids have been advocated to potentially regulate different aspects of AD pathology by facilitating the clearance of amyloid beta (Aβ) from brain. However, the proteinopathy and functional mechanism underlying their molecular interaction in presence of lipid remains poorly understood. Herein, to shed inherent insights into the mode of ApoE3-TREM2 interaction in both lipid and aqueous medium, we have used a combination of different state-of-the-art computational tools including knowledge-based protein–protein docking and molecular dynamics (MD) simulations. Remarkably, we find the direct involvement of regulatory complementarity-determining region-2 (CDR2) loop of TREM2 in interaction with the major hinge region and helix H4 of ApoE3. We further anticipate that ApoE3 attains distinct conformational states and forms an open and extended cavity-like structure in ApoE3-TREM2 complex in presence of lipids. Our data also exhibits reduced hydrophobicity in the ApoE3 binding interface of TREM2, which sets a baseline for reduced binding affinity towards ApoE3. Therefore, we hypothesize that this decline in hydrophobic index might have resulted due to structural variations in the H4 helix and major hinge region leading to altered TREM2 conformation in presence of lipids. Altogether, our findings demonstrate the effect of phospholipids on the structural dynamics and conformation of ApoE3, which contributes to our understanding of how APOE and TREM2 influences the development of AD. However, further experimental studies are necessary to validate and explore our findings which will open up new avenues towards development of novel therapeutic strategies for AD.

Temperature-dependent behavior of poly(N-isopropylacrylamide) brushes via neutron reflectometry

Poly(N-isopropylacrylamide) (PNIPAAm)-modified interfaces are promising for various biomedical applications, however, the PNIPAAm brush structure must be investigated at various temperatures to enable the design of functional PNIPAAm interfaces. In this study, PNIPAAm brush structures with various densities and chain lengths are prepared via atom-transfer radical polymerization and analyzed using neutron reflectometry. The volume fraction of PNIPAAm exhibits temperature-dependent shrinkage; slight PNIPAAm shrinkage is observed below the lower critical solution temperature (LCST) of PNIPAAm, whereas large shrinkage occurs across the LCST of PNIPAAm. The volume of water in the PNIPAAm brush is 40% even when it is dehydrated at 37 °C and is slightly extended relative to its dry state. The dense PNIPAAm brush is thicker than the diluted PNIPAAm brush because the densely packed PNIPAAm chain tends to form an extended structure. A higher volume fraction of D2O is observed in the diluted PNIPAAm brush than in the dense PNIPAAm brush because the former can accommodate a larger volume of D2O. These results indicate that neutron reflectometry can provide essential information on the PNIPAAm brush configurations with various chain lengths and densities at different temperatures. These findings are applicable to the design of further functional PNIPAAm brush interfaces for biomedical applications.

Molecular basis of global promoter sensing and nucleosome capture by the SWR1 chromatin remodeler.

The SWR1 chromatin remodeling complex is recruited to+1 nucleosomes downstream of transcription start sites of eukaryotic promoters, where it exchanges histone H2A for the specialized variant H2A.Z. Here, we use cryoelectron microscopy (cryo-EM) to resolve the structural basis of the SWR1 interaction with free DNA, revealing a distinct open conformation of the Swr1 ATPase that enables sliding from accessible DNA to nucleosomes. A complete structural model of the SWR1-nucleosome complex illustrates critical roles for Swc2 and Swc3 subunits in oriented nucleosome engagement by SWR1. Moreover, an extended DNA-binding α helix within the Swc3 subunit enables sensing of nucleosome linker length and is essential for SWR1-promoter-specific recruitment and activity. The previously unresolved N-SWR1 subcomplex forms a flexible extended structure, enabling multivalent recognition of acetylated histone tails by reader domains to further direct SWR1 toward the+1 nucleosome. Altogether, our findings provide a generalizable mechanism for promoter-specific targeting of chromatin and transcription complexes.

Constraints on the Gas-phase C/O Ratio of DR Tau's Outer Disk from CS, SO, and C2H Observations

Millimeter wavelength observations of Class II protoplanetary disks often display strong emission from hydrocarbons and high CS/SO values, providing evidence that the gas-phase C/O ratio commonly exceeds 1 in their outer regions. We present new NOEMA observations of CS 5–4, SO 76–65 and 56–45, C2H N = 3–2, HCN 3–2, HCO+ 3–2, and H13CO+ 3–2 in the DR Tau protoplanetary disk at a resolution of ∼0.″4 (80 au). Estimates for the disk-averaged CS/SO ratio range from ∼0.4 to 0.5, the lowest value reported thus far for a T Tauri disk. At a projected separation of ∼180 au northeast of the star, the SO moment maps exhibit a clump that has no counterpart in the other lines, and the CS/SO value decreases to <0.2 at its location. Thermochemical models calculated with DALI indicate that DR Tau’s low CS/SO ratio and faint C2H emission can be explained by a gas-phase C/O ratio that is <1 at the disk radii traced by NOEMA. Comparisons of DR Tau’s SO emission to maps of extended structures traced by 13CO suggest that late infall may contribute to driving down the gas-phase C/O ratio of its disk.

Influence of Magnesium Ion Binding on the Adenosine Diphosphate Structure and Dynamics, Investigated by 31P NMR and Molecular Dynamics Simulations.

Magnesium (Mg2+) is the most abundant divalent cation in the cell and is essential to nearly every biochemical reaction involving adenosine triphosphate (ATP) and its lower energy counterpart, adenosine diphosphate (ADP). In this work, we examine the solution dynamics of ADP at different concentrations and record the changes thereof due to the presence of Mg2+ ions. Relaxation and diffusion experiments were performed on a range of ADP solutions with increasing magnesium concentration. The most significant changes of both relaxation and diffusion behaviors are observed when adding Mg2+ up to 0.5 ADP equivalent (eq), with most of the changes complete at 1 eq. Molecular dynamics simulations also show a significant structure introduced by Mg2+ with very stable pyramidal coordination with the phosphate oxygens. A more extended structure found in the presence of Mg2+ is consistent with the experimental slowing of diffusion and an increase in the spin-lattice relaxation rate. We do not observe direct evidence of aggregation in solution, although translational diffusion is slowed down significantly at higher concentrations (while solvent diffusion remains constant).

A high gain quasi Z‐source based full‐bridge isolated DC‐DC converter with extendable structure for grid‐tied/standalone PV system

AbstractA multi‐input single‐output converter that is based on the impedance network and the standard isolated converters is presented. The topology is named quasi Z‐source full‐bridge isolated converter (qZSFBIC). The proposed topology helps to integrate various renewable power generation systems with a common three‐phase grid‐connected inverter. It was also capable of providing isolation between the input and output circuits in addition to the boost function. The integration of multiple energy sources is achieved using fewer components than conventional converters. As a result, it achieves greater conversion efficiency and has improved circuit characteristics. It offers a larger voltage control range as compared to the conventional ZSC and enhances the input‐output voltage transformation ratio. To determine whether or not the suggested converter is technically feasible, the circuit architecture, operating principle, control mechanism, and simulation results are presented. An improved proportional resonant‐second order general integrator (IPR‐SOGI) has been utilized to provide a gating signal for the voltage source inverter. The 1.5 kW, 400 V, 50 Hz model is designed to authenticate the proposed scheme with qZSFBIC. The results showed that the proposed converter offered double the time of boosting than the conventional ZSC converter and the conversion efficiency is around 89%.

Catena-Poly[[(8-amino-quinoline)-cobalt(II)]-di-μ-azido

The title coordination polymer, [Co(N3)2(C9H8N2)] n , was synthesized solvothermally. The CoII atom exhibits a distorted octa-hedral [CoN6] coordination geometry with a bidentate 8-amino-quinoline ligand and four azide ligands. Bridging azide ligands result in chains extending along [100]. N-H⋯N hydrogen bonds join the chains to give an extended structure with sheets parallel to (002).

Strongly bound anions featuring bismuth fluoride building blocks

The stability of polynuclear superhalogen anions composed of BiF5 building blocks was investigated using ab initio electronic structure methods and flexible basis sets. A comprehensive exploration of the ground state potential energy surfaces of (Bi2F11)−, (Bi3F16)− and (Bi4F21)− anions, which can be viewed as comprising BiF5 fragments and an additional fluorine atom, led to the identification of their isomeric structures. It was found that the most stable isomers, predicted to dominate at room temperature, correspond to chain-like extended structures containing BiF6 subunits, with fluorine ligands arranged octahedrally around Bi atoms, sharing F atoms to form Bi–F–Bi bridging linkages. The vertical electron detachment energies of the (BinF5n+1)− anions (n = 1–4) were found to be very high (ranging from 10.91 to 13.36 eV) and increased with the number of bismuth atoms (n) and thus the BiF5 building blocks involved in the structure. Thermodynamic stability of the (BinF5n+1)− anions (i.e., their susceptibility to fragmentation) was also verified and discussed.

Multiferroicity in plastically deformed SrTiO3

Quantum materials have a fascinating tendency to manifest novel and unexpected electronic states upon proper manipulation. Ideally, such manipulation should induce strong and irreversible changes and lead to new relevant length scales. Plastic deformation introduces large numbers of dislocations into a material, which can organize into extended structures and give rise to qualitatively new physics as a result of the huge localized strains. However, this approach is largely unexplored in the context of quantum materials, which are traditionally grown to be as pristine and clean as possible. Here we show that plastic deformation induces robust magnetism in the quantum paraelectric SrTiO3, a property that is completely absent in the pristine material. We combine scanning magnetic measurements and near-field optical microscopy to find that the magnetic order is localized along dislocation walls and coexists with ferroelectric order along the walls. The magnetic signals can be switched on and off via external stress and altered by external electric fields, which demonstrates that plastically deformed SrTiO3 is a quantum multiferroic. These results establish plastic deformation as a versatile knob for the manipulation of the electronic properties of quantum materials.

In LIGO’s Sight? Vigorous Coherent Gravitational Waves from Cooled Collapsar Disks

We present the first numerical study of gravitational waves (GWs) from collapsar disks, using state-of-the-art 3D general relativistic magnetohydrodynamic simulations of collapsing stars. These simulations incorporate a fixed Kerr metric for the central black hole (BH) and employ simplified prescriptions for disk cooling. We find that cooled disks with an expected scale height ratio of H/R ≳ 0.1 at ∼10 gravitational radii induce Rossby instability in compact, high-density rings. The trapped Rossby vortices generate vigorous coherent emission regardless of disk magnetization and BH spin. For BH mass of ∼10 M ⊙, the GW spectrum peaks at ∼100 Hz, with some breadth due to various nonaxisymmetric modes. The spectrum shifts toward lower frequencies as the disk viscously spreads and the circularization radius of the infalling gas increases. Weaker-cooled disks with H/R ≳ 0.3 form a low-density extended structure of spiral arms, resulting in a broader, lower-amplitude spectrum. Assuming an optimistic detection threshold with a matched-filter signal-to-noise ratio of 20 and a rate similar to Type Ib/c supernovae, LIGO–Virgo–KAGRA (LVK) could detect ≲1 event annually, suggesting that GW events may already be hidden in observed data. Third-generation GW detectors could detect dozens to hundreds of collapsar disks annually, depending on the cooling strength and the disk formation rate. The GW amplitudes from collapsar disks are ≳100 times higher with a substantially greater event rate than those from core-collapse supernovae, making them potentially the most promising burst-type GW class for LVK and Cosmic Explorer. This highlights the importance of further exploration and modeling of disk-powered GWs, promising insights into collapsing star physics.

Synthesis and crystal structures of disubstituted ferrocenes carrying bromo and N-heteroaryl substituents

Noncovalent interactions in crystal packing play significant roles in the formation of extended network structures. Thus, this study aims to investigate the influence of noncovalent bonds, particularly halogen bonds, on the crystal packing of ferrocene derivatives. For this purpose, disubstituted ferrocene derivatives carrying both bromo and N-heteroaryl substituents, 1‑bromo-1ʹ-(Het)ferrocene [Het = 5-pyrimidyl (1), 2-pyridyl (2), and 4-pyridyl (3)] and 1‑bromo-2-(Het)ferrocene [Het = 5-pyrimidyl (4) and 4-pyridyl (6)], were synthesized. Here, we discuss a comparison of their molecular and crystal structures, with those of a related compound, 1‑bromo-2-(2-pyridyl)ferrocene (5). Although the crystal packings of 1–5 are classified into quasi-one-dimensional chain structures, their intermolecular interactions are different. Compounds 1–3 exhibit Br⋅⋅⋅cyclopentadienyl halogen bonds to form extended structures. In contrast, 4 shows the π–π stacking interactions between the pyrimidine rings of adjacent molecules, and 5 exhibits the Br⋅⋅⋅N halogen bonds between adjacent molecules. The crystal structures contained chiral molecules of opposing handedness.

(Invited) Fullerenes for Bio-Applications: The Way of Water

Nano-materials are emerging as important components for a series of bio-applications. In this context, carbon nanostructures such as graphene, carbon nanotubes and fullerenes have unique chemical and physical properties that make them attractive for such applications. Carbon nanomaterials have been used in tissue engineering, biosensing and drug delivery. They have also shown anti-microbial activity. They can be loaded with drugs for controlled local delivery. More importantly, the surface of carbon nanomaterials can be functionalised to enhance their biocompatibility by increasing their water-solubility.In this talk, I will present an update on our work in using fullerenes and their derivatives for developing bio-nanomaterials. I shall focus on the combination of carbon nanostructures and polymeric materials which can result in supramolecular hydrogels with interesting properties. Hydrogels are emerging as important materials in applications such as cellular scaffoldings in regenerative medicine/tissue engineering, tissue replacements, wound dressings, etc.I will present the synthesis of supramolecular hydrogels made from fullerenes of different sizes (C60, C84 and C90–92) that have been hydroxylated and functionalised with hydrophilic oligoethylene glycol chains. To the best of our knowledge, there have been no attempts made at incorporating higher fullerenes and their derivatives into such extended supramolecular structures, before now.I will also show possibilities for extending our approach to endohedral fullerenes such as N@C60. I will show how we can use advanced techniques including AFM to characterise the elasticity of the hydrogels formed. The ability to incorporate endohedral fullerenes in hydrogels may be important in extending the possibility for using these materials as sensors in vitro or even in vivo, exploiting the quantum properties of such molecular systems such as their extended electron and nuclear spin lifetimes.

Investigating the Effect of Chain Extender on the Phase Separation and Mechanical Properties of Polybutadiene-Based Polyurethane.

The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.

Ion-temperature- and density-gradient-driven instabilities and turbulence in Wendelstein 7-X close to the stability threshold

Electrostatic gyrokinetic instabilities and turbulence in the Wendelstein 7-X stellarator are studied. Particular attention is paid to the ion-temperature-gradient (ITG) instability and its character close to marginal stability [Floquet-type turbulence (Zocco et al., Phys. Rev. E, vol. 106, 2022, p. L013202) with no electron temperature gradient]. The flux tube version of the $\delta f$ code stella (Barnes et al., J. Comput. Phys., vol. 391, 2019, pp. 365–380) is used to run linear and nonlinear gyrokinetic simulations with kinetic electrons. The nature of the dominant instability depends on the wavelength perpendicular to the magnetic field, and the results are conveniently displayed in stability diagrams that take this dependence into account. This approach highlights the presence of universal instabilities, which are less unstable but have longer wavelengths than other modes. A quasi-linear estimate of the heat flux suggests they are relevant for transport. Close to the stability threshold, the linear eigenmodes and turbulence form highly extended structures along the computational domain if the magnetic shear is small. Numerical experiments and diagnostics are undertaken to assess the resulting radial localisation of the turbulence, which affects the interaction of the latter with zonal flows. Increasing the amplitude of the magnetic shear (e.g.through current drive) has a stabilising effect on the turbulence and, thus, reduces the nonlinear energy transport.