“Statistical” symmetry with applications to phase transitions

Hermann proposed that mesomorphic media should be classified by assigning certain statistical symmetry groups to each possible partially ordered array. Two translational groups introduced were called superordinate and subordinate. We find that the average density in such a partially ordered medium has the superordinate symmetry ₁, while the pair correlation function has the subordinate symmetry ₂. A complete listing is made of all compatible combinations of ₁ and ₂ in two and three dimensions. This leads to more possible symmetries than Hermann obtained, e.g., also to nonstoichiometric crystals. The order parameter space for the systems is found to be the quotient space ₁/₂. In most cases it is identical to the order parameter space of low-dimensionalXY spin systems. The Landau free energy is expanded as functional of the two-particle correlation functionK; the translation group is found to be ₁×₂. A Landau mean-field theory can then be carried out by expanding the system free energy into a series of invariants of the active irreducible representations ofK and mapping the free energy onto that for anXY planar spin system. We predict novel critical behavior for transitions between mesomorphic phases and go nogo selection rules for continuous transitions. We give the structure factors for X-ray scattering so changes in all such phase transitions are observable. The statistical symmetry groups, which describe point and translational symmetries of the mesophases, are classified. Proposals are made to include quasi-long-range or topological order in the classification scheme.This work supported in part by National Science Foundation (Division of International Programs), the PSC-BHE—Faculty Research Award CUNY and Deutsche Forschungsgemeinschaft.     

Synthesis and mesomorphic properties of novel tolane-type liquid crystals

Two series of novel tolane-type liquid crystals(LCs) comprising of hydrogen-bonded organic acids were synthesized.The formation of dimerized H-bond LCs was confirmed by IR spectroscopy,and mesomorphic properties of the LCs were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).It was found that the end groups of the liquid crystals as well as the unsaturated rigid core had effect on the mesomorphic properties.     

Syntheses and Mesomorphic Properties of 2-(4'-Alkoxyphenyl)-6-Substituted Benzothiazoles

Introduction Liquid crystals without a double bond bridge between two rings in the linear molecule are more stable chemically and photochemically. Alkyl cyanobiphenyl was synthesized by Richard in 1973. Later, liquid crystals with the strcture of phenylcyclohexane and cyclohexylcyclohexane also appeared. But the liquid crystals     

对甲氧基偶氮苯衍生物的核磁共振表征

用一维１ Ｈ ＮＭＲ、１３Ｃ ＮＭＲ 方法研究了对甲氧基偶氮苯衍生物的结构, 并通过二维１ Ｈ－ １ Ｈ 同核相关谱（ＣＯＳＹ） 、１３ Ｃ－ １ Ｈ 异核相关谱（ ＨＥＴＣＯＲ） 及１３Ｃ－ １ Ｈ 异核远程相关谱进一步地确定了该类衍生物的１ Ｈ 谱和１３ Ｃ 谱中各谱峰的归属, 为研究侧链液晶聚合物结构提供了有价值的数据。     

Synthesis and mesomorphic properties of 4-(4-bromopropyloxy)-4’-(4-alkyloxybenzylidene)anilines

This article describes the preparation and liquid crystalline properties of a new homologous series of 4-（4-bromopropyloxy）-4’- （4-alkyloxybenzylidene）anilines in which the phenyl ring is armed by a bromopropyloxy chain.The thermal behavior and mesomorphic properties of the synthesized compounds were studied with particular attention given to the correlation between their phase transition temperatures and anisotropic change influenced by molecular structure.All the members displayed enantiotropic smectic phase except for the homologue with the longest alkyloxy chain(R = C₁₈H₃₇),exhibiting only monotropic characteristic. The presence of bromine atom from the propyloxy side chain is found to be capable of altering and influencing the mesomorphic properties.     

The characterization of molecular orientation in PVC with emphasis on the use of Raman spectroscopy

A comparison is given of various methods for studying orientation in polymers, with particular reference to PVC. The Raman method and its application to PVC are described in more detail. The results of a study on PVC samples containing 0—20 pph of dioctyl sebacate plasticizer uniaxially drawn at various temperatures in the range 0 to 90°C are summarized. In this work the orientation of the crystalline regions was studied. More recent investigations are briefly discussed in which the orientation of short all-trans noncrystalline syndiotactic segments is investigated and in which Young's modulus of oriented samples is measured for correlation with the Raman data.     

液晶性芳族共聚酯的DSC研究

<正> 近年来热致液晶性的全芳族共聚酯的研究受到了人们的极大的关注,某些具有刚性主链和主链上包含介晶段的聚酯能显示出热致液晶性,这种高聚物在熔融态表现出自发取向的倾向,通过简单熔融纺丝有希望制备出高强、高模纤维。     

Heterocyclic benzoxazole-based liquid crystals:Synthesis and mesomorphic properties

New Schiff base liquid crystals containing benzoxazole core and alkanoyloxy chain at the end group of the molecules (C_n-1H_2n-1COO-,n=14,16,18) was synthesized.The present compounds are enantiotropic smectic A liquid crystals.It was also found that the end groups of the molecules and polar chloro substituent at the benzoxazole fragment had effect on the mesomorphic properties.     

Synthesis,characterization and comparative study of mesomorphic properties of some new compounds containing both 1,2,4- and 1,3,4-oxadiazole moieties linked in the same molecule

One new homologous series of compounds containing 1,2,4- and 1,3,4-oxadiazole rings in the same molecule was synthesized. 3-(4-Butoxyphenyl)-5-{4-[5-(4-alkoxyphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-1,2,4-oxadiazole (VII)_1–8 were synthesized by several procedures. This series has been characterized by FT-IR and ¹H NMR spectroscopy. Their liquid crystalline properties were studied by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). This series did not show any liquid crystalline behaviors and only crystal to isotropic liquid transition was observed.     

热固性丙烯酸酯液晶

介绍了热固性丙烯酸酯液晶单体的合成路线、取向方式和聚合工艺，叙述了数种影响热固性丙烯酸酯液晶单体及其聚合物性能的主要因素，简要介绍了国内外热固性丙烯酸酯液晶研究的最新动向。