"我"——"三草酸合铁(Ⅲ)酸钾晶体"的生长及影响因素

This article tries to personify potassium ferrioxalate crystal as "I" to describe the formation process and the factors affecting the growth of potassium ferrioxalate crystal. After growing into beautiful green crystals, I dreamed I was participating in the jewelry beauty contest. A serious of wonderful conversations between emerald and I revealed the properties and applications of potassium ferrioxalate crystal. It inspires and guides students to understand the growth of crystals and their properties, and it also stimulates students' interest in studying chemistry.     

Basic modes of three-dimensional polymer crystal associations: Interlocked single crystals and crystal halves

Tridimensional associations of lamellar polymer single crystals, grown from dilute solutions, are described as derived from their sedimentation patterns. These associations include interlocked crystals and decorating crystal halves. The origin of these crystals and their mutual orientation are discussed and tentatively interpreted by specific interactions between the fold surface and the crystallizing chains.     

Simple cubic super crystals containing PbTe nanocubes and their core-shell building blocks

We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge.     

Recent Progress in Polycyclic Aromatic Hydrocarbon‐Based Organic Co‐Crystals

Recently, the development of polycyclic aromatic hydrocarbon ( PAH )‐based organic co‐crystals has attracted increasing interest due to their unique packing modes, optic‐electronic properties and various potential applications in electronic, optic‐electronic and magnetic devices. In this account, we mainly discuss the definition, classification, packing patterns, preparation methods, and applications of PAH‐based co‐crystals. Specifically, the main categories of PAH‐based organic co‐crystals, the frequent methods to prepare them, three main packing patterns, their optical and electrical properties, and their potential applications will be presented. Finally, an outlook of this field is provided.     

Biologically Controlled Morphology and Twinning in Guanine Crystals

Guanine crystals are widely used in nature as components of multilayer reflectors. Guanine‐based reflective systems found in the copepod cuticle and in the mirror of the scallop eye are unique in that the multilayered reflectors are tiled to form a contiguous packed array. In the copepod cuticle, hexagonal crystals are closely packed to produce brilliant colors. In the scallop eye, square crystals are tiled to obtain an image‐forming reflecting mirror. The tiles are about 1 μm in size and 70 nm thick. According to analysis of their electron diffraction patterns, the hexagon and square tiles are not single crystals. Rather, each tile type is a composite of what appears to be three crystalline domains differently oriented and stacked onto one another, achieved through a twice‐repeated twinning about their ⟨011⟩ and ⟨021⟩ crystal axes, respectively. By these means, the monoclinic guanine crystal mimics higher symmetry hexagonal and tetragonal structures to achieve unique morphologies.     

Dissipative crystallization of sodium salts of poly (d-glutamic acid), poly (l-glutamic acid), and their low molecular weight analogs

Drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solution of sodium salts of poly (d-glutamic acid), poly (l-glutamic acid), and their low molecular weight analogs, monosodium d-glutamate, monosodium l-glutamate, and monosodium dl-glutamate. The low molecular weight analogs were hygroscopic and their drying patterns were observed in a dry box coexisted with the bags of desiccant. The broad rings, which are the typical macroscopic drying patterns, were observed for all the samples. Optical isomeric effects on the drying patterns were not recognized. Spherulite (or hedrite) and rod-like crystals from the assemblies of helical main chains of the polymers are formed mainly at the inner area from the broad ring (except central area) and the broad ring area, respectively. Coexistence of sodium chloride enhanced the crystal structures by the cooperative interactions between the polymers and the salts. The typical dissipative crystallization such as accumulation, segregation, and orientation effects of crystals were observed in the drying patterns.     

Liquid-crystal nanoscience: an emerging avenue of soft self-assembly

Liquid crystals are finding increasing applications in a wide variety of fields including liquid-crystal display technology, materials science, bioscience, etc., apart from acting as prototype self-organizable supramolecular soft materials and tunable solvents. Recently, keeping in pace with topical science, liquid crystals have entered into the fascinating domains of nanoscience and nanotechnology. This tutorial review describes the recent and significant developments in liquid-crystal nanoscience embracing contemporary nanomaterials such as nanoparticles, nanorods, nanotubes, nanoplatelets, etc. The dispersion of zero-, one- and two-dimensional nanomaterials in liquid crystals for the enhancement of properties, liquid-crystalline phase behavior of nanomaterials themselves, self-assembly and alignment of nanomaterials in liquid-crystalline media, and the synthesis of nanomaterials by using liquid crystals as 'templates' or 'precursors' have been highlighted and discussed. It is almost certain that the 'fourth state of matter' will play more prevalent roles in nanoscience and nanotechnology in the near future. Moreover, liquid-crystal nanoscience reflects itself as a beautiful demonstration of the contemporary theme "crossing the borders: science without boundaries".     

Crystallization of isotactic polystyrene from solution

Difficulties previously encountered in the growth of chain-folded single crystals of isotactic polystyrene suitable for study by electron microscopy and electron diffraction have been overcome using very poor solvents (including atactic polystyrene of low molecular weight). The hexagonal lamellar crystals produced are relatively stable under electron bombardment and, as a consequence, dark-field moiré patterns produced by double diffraction from overlapping layers are easy to study. These patterns show no evidence of differences in lattice spacing between fold and nonfold planes such as have been reported in single crystals of several other polymers. Such differences were attributed to congestion at fold surfaces and their absence in polystyrene, for which the surface energy of fold surfaces is small, supports this interpretation. A comparison of crystallization kinetics of polystyrene crystals grown from good and from poor solvents reveals differences in growth rates of three or more orders of magnitude at comparable supercoolings. This disparity cannot be accounted for by acceptable adjustments of thermodynamic parameters in current theories of crystallization with chain folding. The role of molecular conformation in solution appears to exert an unexpectedly large influence on crystallization rate.     

X-ray scattering on one-dimensional disordered structures

The review shows different treatments and methods for the analysis of the X-ray diffraction patterns from the crystals disordered in one direction; the possibilities, limitations, and applications of each method are discussed. The author also provides the examples of simulation of the diffraction patterns for the crystals, which have the effects on the experimental X-ray patterns related with 1D disordering. Several structural types and different kinds of one-dimensional disorder are considered.     

Theoretical thermo-optical patterns relevant to glass crystallisation

Mie computations are performed to evaluate light scattering on the virtual microstructures relevant to lithium disilicate glass internal crystallisation. The computations are expressed in the form of optical transmission (OT) patterns evolved on a scale of growing lithium disilicate crystals. Input data include the crystals number density, their size, the wavelength of the incident electromagnetic radiation, the indices of refraction of the lithium disilicate glassy and crystalline phases and the thickness of the virtual glass slab. In the computations, the spherical shape of crystals and their random distribution are assumed. The results reveal the quantitative effects of individual input data constants on the overall course of the computed OT patterns. They also relate the computed OT data magnitudes to the corresponding glass crystallinity (α). In addition, they point to singular combinations of the input data constants defining the conditions under which the OT data could potentially stand for the kinetically important α data. Finally, the results aid better recognition of some fundamental as well as practical properties of the optical thermal methods based on the optical transmission measurements.     

Moiré patterns in the electron image of solution-grown polymer crystals

Relative tilt between two similar thin crystals may result in the formation of a moiré pattern in the electron image. Patterns hitherto interpreted as being parallel moirés or rotation moiré obtained from overlapping solution-grown polymer crystals are reconsidered, and it is shown that in some cases a tilt model is more acceptable. The general features of tilt moiré patterns predicted for crystals of this kind are discussed and compared with micrographs appearing in the literature. Methods of distinguishing tilt moiré patterns are indicated, though it is admitted that such experiments would be difficult to complete in the time limited by destruction of the crystal structure under the action of the electron beam. Extinction contours may also sometimes be confused with long-period tilt moiré patterns, and again careful experimentation is required for accurate identification. The model of the structure of solution-grown polyethylene crystals inferred from a tilt moiré interpretation of many of the electron image fringe patterns found in the literature is consistent with that derived from other sources.     

A matrix method for modelling liquid crystal textures

A simple method for modelling the textures of liquid-crystalline phases, recently proposed by Bedford et al., is here rewritten in matrix form. A formal similarity is found between their method and the continuum theory of liquid crystals. Disclination patterns are simulated by solving a modified matrix equation.     

唐代五言律诗句法与诗境

本文对唐五律句法作出全面系统的梳理,首先分出简单主谓、复杂主谓、题评三大类句型,然后找出每一类中最重要的句式共十种,一一加以详细分析。通过与先唐五言句式作比较,作者试图判断这十种句式究竟是化旧为新,还是翻空出奇,从而确定它们各自的审美特性。末节在理论层次上归纳上文对十种句式的分析,揭示唐五律诗人如何开展全方位的句法创新,不仅实现了齐梁五言所追求的“圆美流转”之理想,而且还超越视听之域,创造出“境生象外”这种前所未有的诗境。     

Co‐crystals with Acetylene: Small Is not Simple!

Acetylene is an amazingly versatile component for the formation of co‐crystals. It requires careful handling and special techniques for crystallisation, but the efforts seem to be rewarding when attaining co‐crystals with small molecules as partners. Many basic questions such as the dominance of specific heterogeneous intermolecular interactions, their driving force for the formation of multicomponent crystals instead of neat ones are expected to be easily analysed. The underlying packing patterns and resulting stoichiometries based on the known supramolecular synthons seem to be straightforward for such small molecules and crystal engineering, considered as the prototype of supramolecular synthesis, should be a simple task. Nineteen co‐crystals with acetylene are presented in this paper, some of which have been previously reported individually. An attempt has been made to find features shared by the groups of co‐crystals, including those that could not be co‐crystallised. But in spite of clear ideas and experiences from previous experiments, surprisingly almost none of systems reached our expectations. Our intuitive approach was not fulfilled, which demonstrates that multicomponent crystals even of small molecules will remain a great challenge for theoretical methods and the crystal structures shown herein represent good candidates for future testing. On the other hand, we wish to encourage other groups to present their views on the crystal structures with an unbiased approach that may offer a better explanation than we are able to outline in this article.     

Liquid-crystalline phases of circular superhelical plasmid DNA and their modification by the action of nuclease enzymes

CD spectra of liquid-crystalline dispersions, X-ray diffraction patterns and optical textures of liquid crystals prepared from native superhelical DNA in poly(ethyleneglycol)-containing water-salt solutions before and after treatment of DNA with micrococcal nuclease have been obtained. It was found that condensation of native superhelical DNA is accompanied by the formation of liquid crystals with a non-specific optical texture. After treatment of the DNA, liquid-crystalline dispersions, with Micrococcal nuclease the DNA is able to form two similar types of liquid crystals with abnormal optical activity which differ in the peculiarities of their textures. The data obtained demonstrate the formation of multiple types of liquid crystals from high molar mass double-stranded optically active DNA molecules.     

Biomineralization of sea urchin teeth

The sea urchin tooth, which is composed almost entirely of Mg-enriched CaCO₃, is of particular interest as a model for the study of biomineralization process due to its amazing mechanical toughness and hardness. Our recent work on the formation process, the crystal composition and orientation, and the mechanical properties of sea urchin tooth are summarized in this paper. First, transmission electron microscopy images and electron diffraction patterns, as well as crystal overgrowth experiments, show that the highly convoluted primary plate-lamellar needle complex grows into a single crystal of calcite from a transient amorphous precursor phase in the sea urchin tooth. Amorphous calcium carbonate exists in the center of both the primary plates and the needles, even though the surfaces are already well crystallized. Second, X-ray photoelectron emission spectromicroscopy demonstrates that the needles, primary plates, and polycrystalline matrix crystals are all aligned. And there are two alternating crystal orientations in the stone part of the sea urchin tooth. Microbeam X-ray diffraction patterns further prove the existence of the two crystal orientations in sea urchin tooth. The c axes of calcite in the two oriented crystals are only a few degrees from each other. Third, the mechanical properties of sea urchin tooth grinding tip were studied by nanoindentation. The polycrystalline matrix has a higher elastic modulus and hardness than single crystalline needles and plates. It is proposed that the grinding capability of the tooth can be attributed to the small and uniform sizes of the polycrystalline crystals, their high Mg contents, and the two co-orientations of single crystals and polycrystalline structure. The improved understanding of the biomineralization process of sea urchin tooth and the relations between their structures and mechanical properties may shed light on the design of mechanical grinding and cutting tools with tunable properties.     

原位磁场下粉末样品的X射线衍射图谱

To obtain more crystal and magnetic structural information of powder crystals,magnetic field is introduced into X'Pert-MPD XRD apparatus with the strength of 0. 42 T and two different directions:one direction of magnetic field is vertical to the sample holder and another is parallel. XRD patterns in situ magnetic field are obtained for six samples which are representative of paramagnetic,diamagnetic,ferromagnetic,ferrimagnetic,antiferromagnetic substances and reduction product of FeCl2 by NaBH4 respectively. Compared with XRD patterns obtained in the zero magnetic field,there are some diffraction peaks disappear,some occur,or some diffraction angles and counts change. In addition,the patterns are different under the different direction of magnetic field. The cause is that magnetic dipoles in crystals are oriented along with the direction of magnetic field. The oriented magnetic dipoles produce stress in crystals and make crystal lattice changed（such as magnetostriction）or even turn particles aligned along with the direction of magnetic field to form preferred orientation of particles.     

Bold relief fabrication by means of electroconvection: basic properties of a suitable mixture

Electroconvection of liquid crystals does not only lead to a large variety of spontaneously formed patterns, but these patterns can also be used as a template for the fabrication of polymer surfaces exhibiting a periodic bold relief. Here, a useful room-temperature nematic mixture consisting of two photostable liquid crystals and a photosensitive cross-linker is presented. Its stability diagram in the frequency-voltage plane, the influence of monomer concentration and the topography of the resulting polymer surfaces are described.     

Non‐Brownian Particle‐Based Materials with Microscale and Nanoscale Hierarchy

Colloidal crystals are interesting materials owing to their customizable photonic properties, high surface area, and analogy to chemical structures. The flexibility of these materials has been greatly enhanced through mixing particles with varying sizes, compositions, and surface charges. In this way, distinctive patterns or analogies to chemical stoichiometries are produced; however, to date, this body of research is limited to particles with nanoscale dimensions. A simple method is now presented for bottom‐up assembly of non‐Brownian particle mixtures to create a new class of hierarchically‐ordered materials that mimic those found in nature (both in pore distribution as well as stoichiometry). Additionally, these crystals serve as a template to create particle‐based inverted crystalline structures with customizable properties.