Phase behavior of a substituted poly(paraphenylene): Poly(para-2,5-didecyl-p-phenylene)

The thermal behavior of poly(para-2,5-didecyl-p-phenylene) has been investigated by differential scanning calorimetry and real time X-ray diffraction. Poly(para-2,5-didecyl-p-phenylene) is a semicrystalline material that crystallizes in a layered structure. The system exhibits two thermal transitions in the investigated temperature range. The first one, occurring at lower temperatures, provokes a reduction of the layered spacing accompanied by an appreciable disordering of the lateral side chains. Above the first transition the material is shearable, highly viscous, and birefringent. Thus, we have associated this transition to the formation of a layered mesophase. The higher temperature transition exhibits a twofold endothermic DSC peak and is characterized by the disappearance of X-ray diffracted intensity. At temperatures above the second transition the system presents the characteristics of an isotropic melt. Consequently, we have associated this transition with the complete disordering of the polymeric backbones. By following an appropriate thermal treatment it has been shown that the twofold shape of the endotherm characterizing the higher temperature transition can be changed into a single endotherm. This effect has been interpreted as being due to the kinetics of main-chain ordering. This ordering seems to proceed by the initial growth of domains with a high level of order followed by the subsequent increase of these domains through the inclusion of less ordered material. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 49–54, 1998     

Effect of cellulose nanofiber on the dynamically asymmetric phase separation in epoxy/polysulfone blends

Significant effect of cellulose nanofibers (CNFs) on cure‐induced phase separation in dynamically asymmetric system is reported. An epoxy/polysulfone blends with typical layered structure formation was chosen as the polymer matrix, and morphology evolution and rheological behavior of systems with different nano‐size fiber loadings upon curing reaction were investigated using optical microscopy and rheological measurement. CNF distributed uniformly in the polymer matrix and had good interaction with polymer chains. Curing reaction of epoxy was promoted by CNF, making the system gel and phase separate earlier. Meanwhile, system viscosity was increased with CNF addition, and the movement of polymer chains and component diffusion were constrained, as a result, the structure evolution process was slowed down. The CNF altered the final morphologies, resulting in refined structures with smaller characteristic length scales or even completely change the morphologies from the layered structures to a bicontinuous structure when the CNF concentration reached to a relatively high level. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1357–1366     

Direct Observation of Defect-Aided Structural Evolution in a Nickel-Rich Layered Cathode

Ni-rich LiNi_1−x−yMn_xCo_yO₂ (NMC) layered compounds are the dominant cathode for lithium ion batteries. The role of crystallographic defects on structure evolution and performance degradation during electrochemical cycling is not yet fully understood. Here, we investigated the structural evolution of a Ni-rich NMC cathode in a solid-state cell by in situ transmission electron microscopy. Antiphase boundary (APB) and twin boundary (TB) separating layered phases played an important role on phase change. Upon Li depletion, the APB extended across the layered structure, while Li/transition metal (TM) ion mixing in the layered phases was detected to induce the rock-salt phase formation along the coherent TB. According to DFT calculations, Li/TM mixing and phase transition were aided by the low diffusion barriers of TM ions at planar defects. This work reveals the dynamical scenario of secondary phase evolution, helping unveil the origin of performance fading in Ni-rich NMC.     

高Tc超导体及相关化合物探索研究新进展

所有已知的层状铜氧化合物超导体结构均可按连接单元、分隔单元和三种不同的铜氧平面进行分类，由这几种基本的结构单元也可组合设计出新的结构类型，通过进一步的实验研究可以获得新结构类型的层状铜氧化合物超导体。以这一思想为出发点，本文从材料设计的角度总结了近五年来在新结构层状铜氧化合物超导体探索中的新进展。     

Hydrogen bonded co-crystallised layered isopropanol-pyrogallol[4]arenes

A novel isopropanol-pyrogallol[4]arene forms a layered structure via hydrogen bonding and C–H…π interactions. The layered structure results in encapsulation of one isopropanol molecule. The application of NMR methods to determine solution structures and crystal structures provides insight into host–guest properties and the molecular interactions between them.     

GaFPO3(C6H5): a new fluorinated gallium phenyl­phosphonate with a layered network

Crystals of gallium fluoro­phenyl­phospho­nate were synthesized hydro­thermally at 453 K under autogenous pressure. The solid crystallizes in the monoclinic system and its structure is built up by the connection of zigzag chains of edge‐sharing GaO₄F₂ octahedra to phenyl­phosphonate groups. This results in the formation of a layered structure, in which the phenyl groups point upward and downward from the inorganic sheet. The Ga atoms occupy the special positions 4a (inversion center) and 4e (twofold axis).     

Rheological properties of diblock copolymer/layered‐silicate nanocomposites

The melt‐state viscoelastic properties of nanocomposites prepared with a symmetrical polystyrene–polyisoprene block copolymer and organically modified layered silicates are examined. Nanocomposites based on three thermodynamically equivalent organically modified layered silicates, primarily differing in lateral disk diameter (d), are studied with small‐amplitude oscillatory shear. The effects of the domain structure of the ordered block copolymer and the mesoscale dispersion of the layered silicates on the rheological properties are examined via a comparison of data for the nanocomposites in the ordered and disordered states of the block copolymer. Hybrids prepared with 5 wt % organically modified fluorohectorite (d ～ 10 μm) and montmorillonite (d ～ 1 μm) demonstrate a notable decrease in the frequency dependence of the moduli at low frequencies and a significant enhancement in the complex viscosity at low frequencies in the disordered state. This behavior is understood in terms of the development of a percolated layered‐silicate network structure. However, the viscoelastic properties in the disordered state with 5 wt % organically modified laponite (d ～ 30 nm) and in the ordered state of the block copolymer for all layered silicates demonstrate only minor changes from those observed for the unfilled polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1434–1443, 2002     

Long-Range Cationic Disordering Induces two Distinct Degradation Pathways in Co-Free Ni-Rich Layered Cathodes

Ni-rich layered oxides are one of the most attractive cathode materials in high-energy-density lithium-ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long-range cationic disordering of Co-free Ni-rich Li_1−m(Ni_0.94Al_0.06)_1+mO₂ (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near-surface region of NA particles with very low cation disorder (NA-LCD, m≤0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a “core–shell” structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA-HCD, 0.06≤m≤0.15) that lead to a slow capacity decay upon cycling.     

Synthesis of Layered Hydroxide Zinc m‐Aminobenzoate Compounds and Their Exfoliation Reactions

Two types of layered hydroxide zinc m‐aminobenzoate compounds with structures of layered basic metal salt (LBMS) were prepared by the reaction of zinc hydroxide with m‐aminobenzoic acid solution in the temperature range of 40–120°C. The formation reactions, structures, chemical compositions, and exfoliation reactions of the layered compounds in alcohol solvents were investigated by XRD, TG‐DTA, SEM, and TEM. One layered phase with a basal spacing of 1.08 nm has a α‐Ni(OH)₂‐like structure, and its chemical formula can be written as Zn(OH)_0.67(m‐NH₂C₆H₄COO)_1.33. This phase has strip‐like particle morphology and cannot be exfoliated into its nanosheets in alcohol solvents. The other layered phase with a basal spacing of 2.66 nm has a zinc hydroxide‐nitrate‐like structure, and can be exfoliated in alcohol solvents.     

The Structure and Properties of Graphite Monofluoride Using the Three-Dimensional Cyclic Cluster Approach

In this paper, we present the theoretical study of the crystal and electron structure of an intercalated compound of graphite —the graphite monofluoride {CF}_n. The latter is widely used as a lubricant under extremely high temperatures and high vacuum, and as a successful cathodic depolarizer in batteries with high energy density. The layered structure of the graphite monofluoride has been confirmed, but statistical distributions of the individual layers are possible. This fact helps in understanding the problems linked to an experimental determination of the structure of this material. Small interlayer dissociation energies show that the bonding between the individual layers is mainly due to the weak interlayer electrostatic forces, which explains the excellent lubricant properties of this material. Band structure calculations reveal that, whereas some layer arrangements of the bulk material lead to insulating properties, others have a conductive character. This fact explains the weak overall conductive properties of synthetic graphite monofluoride.     

Structural and thermal properties of Co-Cu-Fe hydrotalcite-like compounds

The structural properties and thermal decomposition processes of Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray diffraction, thermogravimetric measurements, Fourier-transform infrared and Mössbauer spectroscopies. Due to the strong Jahn-Teller effect, the Cu-Fe layered system is stabilized only in the presence of Co²⁺. At low Co²⁺ contents, additional phases are segregated in the solids. X-ray patterns show the presence of Cu(OH)₂ and CuO. The decomposition process was investigated by in situ X-ray, in situ Mössbauer and FTIR experiments. By increasing the temperature from 25 °C up to 180 °C we observed that the structural disorder increases. This effect has been likely attributed to the Co²⁺→Co³⁺ oxidation since thermal decomposition was carried out under static air atmosphere. Part of the Co³⁺ cations could migrate to the interlayer region, thus forming a metastable compound that still has a layered structure. Collapse of the layered structure was observed at about 200 °C. By further increasing the temperature the system becomes more crystalline and the formation of Co₃O₄ is observed in the X-ray patterns. In Cu-rich HT, some of the carbonate anions are released at temperatures higher than 550 °C and this phenomenon is attributed to the formation of a carbonate-rich phase. The specific surface area data present its highest values in the temperature range where the collapse of the layered structure takes place.     

Topochemical Transformations of CaX2 (X=C,Si, Ge) to Form Free‐Standing Two‐Dimensional Materials

Topochemical transformations of layered materials CaX₂ (X=Si, Ge) are the method of choice for the high‐yield synthesis of pristine, defect‐free two‐dimensional systems silicane and germanane, which have advanced electronic properties. Based on solid‐state dispersion‐corrected calculations, mechanisms for such transformations are elucidated that provide an in‐depth understanding of phase transition in these layered materials. While formation of such layered materials is highly favorable for silicane and germanane, a barrier of 1.2 eV in the case of graphane precludes its synthesis from CaC₂ topochemically. The energy penalty required for distorting linear acetylene into a trans‐bent geometry accounts for this barrier. In contrast it is highly favorable in the heavier analogues, resulting in barrierless topochemical generation of silicane and germanane. Photochemical generation of the trans‐bent structure of acetylene in its first excited state (S₁) can directly generate graphane through a barrierless condensation. Unlike the buckled structure of silicene, the phase‐h of CaSi₂ with perfectly planar silicene layers exhibits the Dirac cones at the high symmetry points K and H. Interestingly, topochemical acidification of the cubic phase of calcium carbide is predicted to generate the previously elusive platonic hydrocarbon, tetrahedrane.     

A Highly Water‐Tolerant Magnesium(II) Coordination Polymer Derived from a Flexible Layered Structure

A two‐dimensional (2D) layered Mg^II coordination polymer (CP) with a high tolerance for H₂O was designed, synthesised, and crystallographically characterised. The synthesis was achieved by the introduction of a flexible 2D layered structure composed of Mg^II ions and isonicotinate N‐oxide ligands. Owing to its high H₂O tolerance, the obtained 2D layered structure has the flexibility to repeatedly adsorb a large amount of H₂O associated with interlayer expansion and enable the removal of H₂O from a H₂O/2‐propanol mixed vapour. These results indicate that the CP could be an excellent dehydrating agent.     

Lanthanide‐Based Functional Misfit‐Layered Nanotubes

The synthesis of nanotubes from layered compounds has generated substantial scientific interest. “Misfit” layered compounds (MLCs) of the general formula [(MX)_1+x]_m[TX₂]_n, where M can include Pb, Sb, rare earths; T=Cr, Nb, and X=S, Se can form layered structures, even though each sub‐system alone is not necessarily a layered or a stable compound. A simple chemical method is used to synthesize these complex nanotubes from lanthanide‐based misfit compounds. Quaternary nanotubular structures formed by partial substitution of the lanthanide atom in nanotubes by other elements are also confirmed. The driving force and mechanism of formation of these nanotubes is investigated by systematic temperature and time‐dependent studies. A stress‐inducement mechanism is proposed to explain the formation of the nanotubes. The resulting materials may find applications in fields that include thermoelectrics, light emitters, and catalysis and address fundamental physical issues in low dimensions.     

Construction of Helically Stacked π-Electron Systems in Poly(quinolylene-2,3-methylene) Stabilized by Intramolecular Hydrogen Bonds

π-Stacked polymers, which consist of layered π-electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π-stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π-stacked architecture based on poly(quinolylene-2,3-methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo-copolymerization of an o-allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted-tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic-force microscopy.     

Synthesis,Crystal Structure,and Colloidal Dispersions of Vanadium Tetrasulfide (VS4)

Although many of the layered metal chalcogenides, such as MoS₂, are well‐studied, some other chalcogenides have received less attention by comparison. In particular, there has been an emerging interest in vanadium tetrasulfide (VS₄), which displays useful properties as a component of hybrids. However, the synthetic methods and characteristics of individual VS₄ are not yet well defined, and there is no report on its solution processability. Here we have synthesized VS₄ by a simple and fast direct reaction between elements. Reinvestigation of the VS₄ crystal structure yielded more precise atomic coordinates and interatomic distances, thereby confirming the crystallization of VS₄ in the monoclinic C2/c group and its quasi‐1D chainlike structure. As the chains in VS₄ are only bonded by weak van der Waals forces, we further demonstrate that bulk VS₄ may be ultrasonically dispersed in appropriate solvents to form colloids, similarly to the layered chalcogenides. VS₄ particles in colloids retain their phase identity and rod‐shaped morphology with lengths in the range of hundreds of nanometers. Isopropanol dispersion exhibited the highest concentration and stability, which was achieved owing to the repulsion caused by high negative charges on the edges of the particles.     

The Effect of Interlayer Anion Grafting on Water Oxidation Electrocatalysis: A Comparative Study of Ni- and Co-Based Brucite-Type Layered Hydroxides,Layered Double Hydroxides and Hydroxynitrate Salts

The urge for carbon-neutral green energy conversion and storage technologies has invoked the resurgence of interest in applying brucite-type materials as low-cost oxygen evolution reaction (OER) electrocatalysts in basic media. Transition metal layered hydroxides belonging to the brucite-type structure family have been shown to display remarkable electrochemical activity. Recent studies on the earth-abundant Fe³⁺ containing mössbauerite and Fe³⁺ rich Co−Fe layered oxyhydroxide carbonates have suggested that grafted interlayer anions might play a key role in OER catalysis. To probe the effect of such interlayer anion grafting in brucite-like layered hydroxides, we report here a systematic study on the electrocatalytic performance of three distinct Ni and Co brucite-type layered structures, namely, (i) brucite-type M(OH)₂ without any interlayer anions, (ii) LDHs with free interlayer anions, and (iii) hydroxynitrate salts with grafted interlayer anions. The electrochemical results indeed show that grafting has an evident impact on the electronic structure and the observed OER activity. Ni- and Co-hydroxynitrate salts with grafted anions display notably earlier formations of the electrocatalytically active species. Particularly Co-hydroxynitrate salts exhibit lower overpotentials at 10 mA cm⁻² (η=0.34 V) and medium current densities of 100 mA cm⁻² (η=0.40 V) compared to the corresponding brucite-type hydroxides and LDH materials.     

Preparation and Characterization of TiO2-pillared Layered HNb3O8

IntroductionThelayeredcompoundssuchassmectiteclays,me-tallicphosphatesandtransitionmetaloxidespillaredwithinorganicoxideshavebeenattractingmoreandmoreattentionfrombothacademicandindustrialfieldsduetotheirpotentialapplicationsinadsorption,separa-tion,conductionandparticularlycatalysis.1-7NiobatessuchasKNb3O8andK4Nb6O17,andthecorrespondingprotonicoxides,HNb3O8andH4Nb6O17,aremembersofthefamilyoflayeredtransitionmetaloxidesbasedonoctahedralframeworkstructure,inwhichK+orH+liesbetweenlayersbuil…     

Tetranaphthyleno[5,6‐bcd:11,12‐b′c′d′:17,18‐b′′c′′d′′:23,24‐b′′′c′′′d′′′]tetrafuran

The title compound, C₄₀H₁₆O₄ or [C₁₀H₄O]₄, is a planar tetrameric cyclooligomer which crystallizes in the monoclinic space group P2₁/n. The compound is located on an inversion center with the asymmetric unit consisting of half of the molecule. The compound displays an interesting packing structure, where the cyclooligomer displays both layered packing with respect to nearest neighbors and a rotation of adjacent planar rings that results in additional interactions. The geometric parameters of the compound agree well with those of comparable cyclooligomers, while the packing reveals some similarities and differences.     

Construction of Helically Stacked π‐Electron Systems in Poly(quinolylene‐2,3‐methylene) Stabilized by Intramolecular Hydrogen Bonds

π‐Stacked polymers, which consist of layered π‐electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π‐stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π‐stacked architecture based on poly(quinolylene‐2,3‐methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo‐copolymerization of an o‐allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted‐tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic‐force microscopy.