Spontaneous chirality in simple systems

Two simple examples of spontaneous chiral symmetry breaking are presented. The first is close-packed cylindrically confined spheres. As the cylinder diameter is varied, one obtains a variety of chiral phases. The second example involves unconfined dipolar particles with an isotropic attraction, which also exhibits chiral ground states. We speculate that a dilute magnetorheological fluid film, with the addition of smaller particles to provide an attractive entropic interaction, will exhibit a chiral columnar ground state.     

西佛碱型液晶化合物相变过程中分子排列方式变化的拉曼光谱研究

用变温拉曼光谱对相变过程的研究表明,液晶化合物的初始晶态与熔融后缓慢降温得到的晶态并不吻合,两个状态下分子尾链的构象及刚性核部分的构象不同导致分子的聚集状态不同。西佛碱型液晶化合物VO10相变过程中,在晶态到液晶态相转变过程中,烷氧基尾链链内构象发生突变,同时有序性降低,刚性核部分两个苯环之间的二面角在相变点时发生明显变化,二面角加大。     

Room temperature supramolecular columnar liquid crystals formed by hydrogen bonding of isoquinoline derivatives

We report new self-assembled discotic liquid crystals exhibiting columnar mesophases at room temperature, which are constructed by intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene or 1,3,5-cyclohexanetricarboxylic acid and the peripheral molecules of isoquinoline derivatives. The mesomorphic properties of supramolecular liquid crystals were investigated by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction studies. The self-assembled liquid crystals exhibited rectangular columnar phases (Col_ro) with an ordered stacking structure of the mesogens in a column at room temperature, regardless of the type of the core molecule, due probably to the close-packed aromatic rings around a core molecule and the angular structure in three arms of the discotic mesogen. These room temperature columnar phases are rare examples for the discotic liquid crystals, and our findings in the present study provide a new way to prepare low melting columnar liquid crystalline materials for molecular electronics.     

Entropy-driven formation of a chiral liquid-crystalline phase of helical filaments

We study the liquid-crystalline phase behavior of a concentrated suspension of helical flagella isolated from Salmonella typhimurium. Flagella are prepared with different polymorphic states, some of which have a pronounced helical character while others assume a rodlike shape. We show that the static phase behavior and dynamics of chiral helices are very different when compared to simpler achiral hard rods. With increasing concentration, helical flagella undergo an entropy-driven first order phase transition to a liquid-crystalline state having a novel chiral symmetry.     

Recent results on some columnar paramagnetic metallomesogens

The liquid crystalline and selected physical properties of some vanadyl and manganese(III)-porphyrin-TCNE complexes are discussed. These materials form linear chains from a magnetic point of view and columnar discotic LC phases. Some of the manganese complexes exhibit a bulk magnetic phase below ∼20 K. The discussed materials are studied by means of DSC, X-ray powder diffraction, dielectric spectroscopy, reversal current characterization and magnetic susceptibility measurements. A broader view on some physical properties of columnar paramagnetic metallomesogens is given.     

Effect of the chiral chain length on structural and phase properties of ferroelectric liquid crystals

Studies of structural and phase properties obtained on several ferroelectric liquid crystalline materials with 2-alkoxypropionate group used as a chiral centre and without any lateral substitution are presented. In dependence on the chiral chain length these compounds exhibit the cholesteric N* phase, the ferroelectric smectic C* and a low-temperature SmX phase. Values of the spontaneous polarization and spontaneous tilt angle have been determined within the whole range of the SmC* phase. A low-temperature SmX phase has been identified as the orthogonal hexatic SmB* phase. The molecular parameters, namely the layer spacing in the SmC* and SmB* phases and the average intermolecular distances (D) between neighbouring parallel molecules in all investigated phases have been determined using the results of the X-ray diffraction obtained on non-oriented samples. The effect of the chiral chain length on mesomorphic, structural and physical properties of the studied ferroelectric liquid crystalline materials is discussed.     

Tuning the phase diagrams: the miscibility studies of multilactate liquid crystalline compounds

Design of binary and multicomponent liquid crystalline mixtures is a very powerful tool to reach the desired self-assembling properties. Beyond many advantages, this method has a distinct negativity – it is very material-consuming. While working with unique chiral materials in the research laboratory, this problem can be solved by applying miscibility study by the contact preparation method. In this work, the miscibility studies of lactic acid derivatives and non-chiral/chiral liquid crystalline molecules of different structure have been done in order to establish the phase diagrams. Special attention is focused on the ferro(antiferro)electric smectic phases.     

Study on optical characterization of TGB and reentrant smectic-A phases in binary mixture of two liquid crystals

In this work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds, namely, cholesteryl nonanoate and p-methoxybenzylidene-p-ethylaniline, which exhibits a very interesting liquid crystalline twisted grain boundary (TGB) phase and reentrant smectic-A phase. The chiral liquid crystalline TGB phases and reentrant smectic-A phases have been observed at different concentrations and at different temperatures. The existence of TGB and reentrant smectic-A phases is confirmed by differential scanning calorimetry and optical microscopic studies. The variation of optical anisotropy has been discussed. The helical pitch of the cholesteric phase has also been discussed.     

Isotropic to ferroelectric and antiferroelectric liquid crystals phase transitions

This review is an attempt towards a unified picture of the direct transitions from the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases formed by rod-like and bent-core molecules. The Landau–Ginzburg theories of the phase transitions between the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases in compounds composed of chiral rod-like molecules and achiral bent-core molecules are presented. This includes a discussion of the nature of the order parameters and the nature of the various types of phase transitions. The various predictions are compared with the available experimental results.     

Critical behavior of three-dimensional frustrated helimagnets

The critical properties of classical frustrated helimagnets with different numbers of chiral order parameters are studied in three dimensions. The model of an antiferromagnet on a simple cubic lattice is considered with additional competing exchange interactions between spins of the first and the third range orders. In this model, helicoidal ordered phases exist with one, two, and three independent chiral order parameters. In all cases, it was found that a transition from an ordered to a disordered phase is a single first-order transition in the absence of partially ordered phases.     

Self-diffusion of rodlike viruses through smectic layers

We report the direct visualization at the scale of single particles of mass transport between smectic layers, also called permeation, in a suspension of rodlike viruses. Self-diffusion takes place preferentially in the direction normal to the smectic layers, and occurs by quasiquantized steps of one rod length. The diffusion rate corresponds with the rate calculated from the diffusion in the nematic state with a lamellar periodic ordering potential that is obtained experimentally.     

Counterion phase transitions in dilute polyelectrolyte solutions

In dilute solutions of rodlike polyelectrolytes some counterions are distributed far from polyions while others are located in their vicinity in the regions of cylindrical symmetry of the electrostatic potential. For these cylindrical regions around rodlike polyelectrolytes we find an exact solution of the nonlinear Poisson-Boltzmann equation for the case of nonzero net charge in these regions. This exact solution implies three qualitatively different phases of counterion distribution around the polyions with second order phase transitions between these phases.     

Orientational order of molecular assemblies on inorganic crystals

Surfactant micelles form oriented arrays on crystalline substrates although registration is unexpected since the template unit cell is small compared to the size of a rodlike micelle. Interaction energy calculations based on molecular simulations reveal that orientational energy differences on a molecular scale are too small to explain matters. With atomic force microscopy, we show that orientational ordering is a dynamic, multimolecule process. Treating the cooperative processes as a balance between van der Waals torque on a large, rodlike micellar assembly and Brownian motion shows that orientation is favored.     

Fabrication of NiO photoelectrodes by aerosol‐assisted chemical vapour deposition (AACVD)

Nanostructured nickel oxide (NiO) photoelectrodes were fabricated with controlled morphology and texture using single‐step aerosol‐assisted chemical vapour deposition (AACVD). The durable one‐step film fabrication process resulted in highly crystalline columnar structure. Texture controlled films were also fabricated from granular to crystalline columnar morphology by controlling the deposition temperature. The thin film electrodes are highly reproducible and possess an optical bandgap of ～3.7 eV and exhibit cathodic photocurrent. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

原子核层次的手征对称性

对称性及其破缺是基本的科学问题。手征对称性在自然界中广泛存在,大至星系旋臂、行星自转,小到矿物晶体、有机分子、基本粒子,都与手征对称性密切相关。原子核层次的手征对称性概念于1997年提出,随后成为核物理研究的热点问题。目前,实验上已经在核素图上的80,100,130和190质量核区发现了30多例可能具有手征对称性的原子核。简要介绍原子核中的手征对称性概念;手性原子核的预言、识别以及实验验证;并通过展示手性原子核结构的多样性（M_χD）,回顾了理论和实验研究进展;介绍最新发现的原子核中手性和空间反射对称性的联立自发破缺,对未来手性原子核研究的前景进行了展望。Symmetry and its breaking are basic scientific problems. Chiral symmetries are common in nature, for example, the macroscopic spiral arms of galaxies and the rotation of planets; the microscopic spirals of the mineral crystalline, the organic molecules and the elementary particles. The concept of chirality in atomic nuclei was first proposed in 1997. Since then many efforts have been made to understand chiral symmetry and its spontaneous breaking in atomic nuclei. Up to now, more than 30 candidates of chiral nuclei have been reported in the 80, 100, 130, and 190 mass regions. The concept of the chirality in atomic nuclei, the prediction, the signal, and the experimental verification of the chiral nuclei are briefly introduced; the recent theoretical and experimental progress are reviewed, in particular the existence of multiple chiral doublets (M_χD), i.e., more than one pair of chiral doublet bands in one single nucleus; the simultaneous spontaneous breaking of chiral and reflection symmetry in the newly observed atomic nuclei is introduced, together with a prospect on the future study on nuclear chiral symmetry.     

Fractional quantum hall effect in infinite-layer systems

Stacked two dimensional electron systems in transverse magnetic fields exhibit three dimensional fractional quantum Hall phases. We analyze the simplest such phases and find novel bulk properties, e.g. , irrational braiding. These phases host "one and a half" dimensional surface phases in which motion in one direction is chiral. We offer a general analysis of conduction in the latter by combining sum rule and renormalization group arguments, and find that when interlayer tunneling is marginal or irrelevant they are chiral semimetals that conduct only at T > 0 or with disorder.     

Symmetry of electrostatic interaction between pyrophosphate DNA molecules

We study chiral electrostatic interaction between artificial ideal homopolymer DNA-like molecules in which a number of phosphate groups of the sugar-phosphate backbone are exchanged for the pyrophosphate ones. We employ a model in which the DNA is considered as a one-dimensional lattice of dipoles and charges corresponding to base pairs and (pyro)phosphate groups, respectively. The interaction between molecules of the DNA is described by a pair potential U of electrostatic forces between the two sets of dipoles and charges belonging to respective lattices describing the molecules. Minima of the potential U indicate orientational ordering of the molecules and thus liquid crystalline phases of the DNA. We use numerical methods for finding the set of minima in conjunction with symmetries verified by the potential U . The symmetries form a non-commutative group of 8th order, S . Using the group S we suggest a classification of liquid crystalline phases of the DNA, which allows several cholesteric phases, that is polymorphism. Pyrophosphate forms of the DNA could clarify the role played by charges in their liquid crystalline phases, and open experimental research, important for nano-technological and bio-medical applications.     

Two-step melting of the vortex solid in layered superconductors with random columnar pins

We consider the melting of the vortex solid in highly anisotropic layered superconductors with a small concentration of random columnar pinning centers. Using large-scale numerical minimization of a free-energy functional, we find that melting of the low-temperature, nearly crystalline vortex solid (Bragg glass) into a vortex liquid occurs in two steps as the temperature increases: the Bragg glass and liquid phases are separated by an intermediate Bose glass phase. A suitably defined local melting temperature exhibits spatial variation similar to that observed in experiments.     

Bragg-regime engineering by columnar thinning of chiral sculptured thin films

Using a microscopic-to-continuum model of sculptured thin films (STFs) as two-phase composite materials, we have examined the optical consequences of post-deposition, uniform, columnar thinning of chiral STFs. Our results indicate that thinning processes such as etching and bioreduction can be useful in engineering the Bragg regimes of STFs after deposition. Uniform columnar thinning blue-shifts the Bragg regime and can improve the Bragg features of a chiral STF.     

Phase transitions in binary mixtures of rodlike colloids and stiff polymers

A suspension of long rodlike colloids and long stiff polymers is modelled as a mixture of hard rods. The diameter of the colloid particle is finite, while the polymer is considered in the limit of zero diameter. Two types of first-order phase transition may occur in such mixtures: an isotropic-nematic phase transition if the density (or the pressure) is high enough, and a demixing transition involving two isotropic phases. The demixing transition has a critical point, and a triple point with one nematic and two isotropic phases may also exist. Phase diagrams are calculated. For the demixing isotropic-isotropic transition to be observed the ratio between the polymer length and the colloid length must exceed 0.36.