Phase Diagrams of New Compounds with Nematic Reentrant Mesophases

Two new series of compounds exhibiting nematic and smectic reentrant mesophases are presented here; the first one is 4-n-alkoxy benzoyloxybenzylidene 4'-cyanoaniline series the second one the 1-(4-n-alkylbenzoyloxyphenyl) 2-(4'-cyanophenyl) ethane series. Isobaric binary phase diagrams are plotted for each compound by means of the contact method and the mesophases so identified.     

Occurrence of Reentrant Nematic and Reentrant Smectic A Phases in Mesogenic Series

A systematic comparative study of several series of chemically neighbouring compounds apt to give a reentrant mesomorphism is proposed. Experimental data concerning the various reentrant phases are summed up. From these observations various factors favourable to the occurence of the reentrance are revealed. Thus, the chemical composition, the sense and the location of dipoles in the molecules, the reduced temperatures, the length of the rigid core are discussed as relevant parameters.     

Measurements of dc Kerr Constants for a Homologous Series of Nematic Compounds

The dc Kerr constants of seven p,p′-n-alkoxyazoxybenzene homologous compounds have been measured as functions of temperature in the isotropic phase. The observed pretransitional behavior near the isotropic-nematic transition is consistent with the phenomenological model of Landau-de Gennes with the Onsager's loal-field correction included in the dielectric tensor. The dc polarizability anisotropy and the average orientation of the permanent dipole with respect to the long molecular axis are deduced from the experimental results. Their variations with increase of methylene groups in the alkyl chains are discussed.     

New Mesogenic Compounds Exhibiting a Thermotropic Optically Isotropic Phase

Abstract

The only two series of carboxylic acids, 3-nitro- or 3-cyano-4-alkoxybiphenyl-4′-carboxylic acid, are known to exhibit the optically isotropic phase (S_D). Now we synthesised 4-(branched alkoxy)-anilinebenzylidene-4′-carboxylic acid series, all being racemic, and investigated their mesophase properties by means of DSC, optical microscopy and X-ray measurement. As a result, some branched azomethine derivatives were found to form a S_D phase. We also synthesised cinnamic acid derivatives with branched alkoxy tail that were turned out to exhibit either S_D phase or hexagonal columnar phase. We tried biphenyl or azobenzene core analogues which were found to produce a highly ordered smectic phase or no mesophase, respectively. At this stage, we suppose it plays an important role that the branch is introduced into the terminal chain and a certain dipole moment is located within the mesogenic core. These factors may allow the peculiar molecular packing that causes an optically isotropic property.     

常压化学水解反应生长氧化锌晶体

采用ZnCl2·2H2O在常压下高温水解反应生长ZnO晶体,反应温度为500℃.当以SiC为衬底时,可以获得六棱柱形氧化锌晶体,直径约为10μm,长为30～100 μm.当衬底为蓝宝石时,氧化锌沿[0001]呈定向柱状生长,柱的直径为5～10 μm,柱之间具有较多的内部缺陷.当以ZnO为衬底时,在{0001}面,形成连续膜,表面扫描电镜分析表明,晶体具有明显的极性生长特征,[0001]方向呈螺旋柱状生长.在{0001}面,晶体的平整性较好,呈现台阶性生长.     

纳米氮化铝常压溶剂热合成及其光致发光

低温常压下,在有机溶剂中制备出了氮化铝纳米晶.通过XRD、FTIR和定域电子衍射分析,样品中立方相和六方相共存;经XRD和TEM分析,样品中颗粒的平均粒度约为50nm;在样品的PL谱中,在475nm有一个非常强的由氮空位引起的发射峰,而在550nm有一个由AlN的本征缺陷及纳米颗粒的表面效应引起的宽且弱的发射峰.     

First Examples Exhibiting both Double Melting Behavior and Mesomorphism in a Series of Long Chain Substituted Compounds: 1,3-Di(p-n-alkoxyphenyl)propane-1,3-dione

A new series of β-diketones substituted by the same kind of chains, (alkoxy groups) having different lengths (C_nO-Diketone, n = 1-12), has been synthesized. It was found that C_nO-Diketone shows triple melting behavior for n = 1, double melting behavior for n = 2-7, and smectic mesomorphism for n = 8-12. It is the first example exhibiting both double (triple) melting behavior and mesomorphism in a series of long chain substituted compounds, so far as we know. Furthermore, it is noteworthy that the critical change from double melting behavior to mesomorphism occurs between n = 7 and n = 8, which is also the first example in the long chain substituted compounds, so far as we know.