Pattern of liquid crystalline droplets induced by two beam interference in azobenzene derivative

A pattern of liquid crystalline droplets dispersed in the isotropic liquid can be formed during illumination by two interfering laser beams in certain range of the temperature and the light intensity. Azobenzene derivative substituted by long alkyl and alkoxy chains exhibiting smectic phases has been used for the study. The pattern can be reversibly erased and rewritten by shutting down and opening of the interfering beams. Polarized microscope images have shown the formation of numerous liquid crystalline droplets at bright regions of the interference fringes. Influence of the temperature and the light intensity has been studied by measuring the diffraction efficiency dynamics. Photothermal and photoorientational mechanisms of the formation of liquid crystalline droplets pattern have been proposed and discussed.     

Characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of new chiral (S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino(methyl]phenol liquid crystalline compound

Synthesis, characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of a new chiral liquid crystalline compound are presented in this work. This new compound has prolate molecules and exhibits the chiral smectic C* mesophase in a sufficiently large temperature interval. Two types of solid crystalline phases have been found in this compound. Typical textures and temperatures of the direct and reverse phase transitions, taking place in the compound, are given. Typical peculiarities for the first-order transition between the smectic C* mesophase and isotropic liquid have been observed.     

Rheology and flow-induced liquid crystal phase transitions in thermotropic polyethers

This work investigates the interdependence of the phase behaviour, viscosity, temperature, molecular weight and shear rates of thermotropic liquid crystalline polyethers. The viscosity of the isotropic and nematic phases are quantitatively compared; a positive variation in viscosity with respect to temperature is found, with the isotropic viscosity being about an order of magnitude higher than the liquid crystalline viscosity. The dependence of viscosity upon molecular weight of well defined fractions is investigated in both the liquid-crystal and isotropic phases. In the liquid crystalline state the viscosity scales with M ^3.5–5. Variations in the viscosity due to temperature changes affect the isotropic phase more than the liquid crystal phase. No evidence for a negative first normal stress difference is seen. Finally, it is shown how the phase diagram of the material can be altered by shearing the material in the isotropic phase. This is evident by the onset of a shear thinning region at temperatures slightly above T _i, which can be attributed to the formation of shear induced liquid crystallinity.     

Photopyroelectric Calorimetry Investigations of 8CB Liquid Crystal–Microemulsion System

In this work, the photopyroelectric technique has been used to investigate the phase transitions in a liquid crystal microemulsion by combining the simultaneous high temperature resolution thermal diffusivity measurements and optical polarization microscopy observations. It has been found that, during the conversion from the isotropic phase into the nematic one, the micelles are expelled from the nematic domains and remain confined in islands of isotropic material which survive down to the smectic temperature range. A hysteresis in the thermal diffusivity profiles between heating and cooling run over the isotropic–nematic transition temperature range has been observed which has been ascribed to the different micelles distribution into the sample volume during cooling and heating runs. Finally, the almost bulk-like behavior of the thermal diffusivity over the nematic–smectic phase transition confirms that a significant fraction of the micelles are expelled during the nucleation of the nematic phase.     

基于季戊四醇的二代硅碳烷液晶树状物研究——端基含36个4-硝基偶氮苯基团

以基于季戊四醇的二代硅碳烷树状氯化物PCSi-2G-Cl为脚手架、4-硝基-4'-羟己氧基偶氮苯(M-NO2)为介晶基元, 合成了以季戊四醇为核、端基含36个硝基偶氮苯的新型硅碳烷液晶树状物PCSi-2G-NO2.利用红外光谱(IR)、核磁共振(1H NMR)、元素分析(EA)、偏光显微镜(POM)和差示扫描量热法(DSC)进行了表征,PCSi-2G-NO2显示近晶相, 其液晶相行为是K57SE76SA111I110SA75SE56K.而对应的介晶基元M-NO2则为向列相,树状物与修饰单元在熔点、清亮点和液晶态温度区间等方面也存在较大差异.     

Self‐Regulated Smectic Emulsion with Switchable Lasing Application

A structurally reversible smectic liquid crystal (LC) emulsion made of semifluorinated rod‐type molecules in silicon oil, which is controlled by simple heating and cooling, is presented. Without adding any kind of additives, such as surfactants, polymers or emulsifiers, and without using any special tools, such as microfluidics or gas bubbling, the LC molecules spontaneously form monodisperse spherical and myelin‐like structures upon cooling from the isotropic temperature. The LC emulsion can easily trap guest materials, providing a platform for repeatable and reliable switchable emulsification. For example, this interesting system enables the realization of an on–off lasing system by confining fluorescent dyes in the LC droplets.     

功能侧链液晶聚丙烯酸酯及聚丙烯酰胺的合成

基于国内外最研究文献，系统论述了两种新型功能性液晶聚合物－侧链液晶聚丙烯酸酯及聚丙酰胺的合成方法，大分子链结构及其液晶相转变温度，指出这类聚合物合成方法简单，一般显示热致性向列型或近晶型液晶相，液晶相转变温度和液晶态温度范围随链结构的不同发生显著变化。     

功能侧链液晶聚丙烯酸酯的性能及应用前景

基于国内外最新研究文献，系统论述了新型功能性侧链液晶聚丙烯酸酯的液晶性质，光电性质及应用前景，指出这类聚合物一般显示热致性向列型或近晶型液晶相，液晶相转变温度和液晶态温度范围随链结构的不同发生显著变化，具有较短的电场及光场响应时间，对某些有机物质具有选择吸附能力。可望用作光学信息储存材料，气相色谱固定相材料以及复合材料的界面改性材料等。     

Are liquid crystalline properties of nucleosomes involved in chromosome structure and dynamics?

Nucleosome core particles correspond to the structural units of eukaryotic chromatin. They are charged colloids, 101 Angstrom in diameter and 55 Angstrom in length, formed by the coiling of a 146/147 bp DNA fragment (50 nm) around the histone protein octamer. Solutions of these particles can be concentrated, under osmotic pressure, up to the concentrations found in the nuclei of living cells. In the presence of monovalent cations (Na(+)), nucleosomes self-assemble into crystalline or liquid crystalline phases. A lamello-columnar phase is observed at 'low salt' concentrations, while a two-dimensional hexagonal phase and a three-dimensional quasi-hexagonal phase form at 'high salt' concentrations. We followed the formation of these phases from the dilute isotropic solutions to the ordered phases by combining cryoelectron microscopy and X-ray diffraction analyses. The phase diagram is presented as a function of the monovalent salt concentration and applied osmotic pressure. An alternative method to condense nucleosomes is to induce their aggregation upon addition of divalent or multivalent cations (Mg(2+), spermidine(3+) and spermine(4+)). Ordered phases are also found in the aggregates. We also discuss whether these condensed phases of nucleosomes may be relevant from a biological point of view.     

含有双酚-S基团的液晶双马来酰亚胺的合成与表征

合成了一种含有双酚-S基团的液晶双马来酰亚胺(BPSBMI),并利用傅立叶红外光谱(FT-IR)、核磁共振氢谱(1H-NMR)、差示扫描量热分析(DSC)以及热台偏光显微镜(HSPM)对其结构和液晶行为进行了表征。结果表明,合成的含有双酚-S基团的双马来酰亚胺结构符合分子设计,具有向列态球粒织构。     

Infrared spectroscopic characterization of orientation and order of thin oligothiophene films

Thin films (2–100 nm) of oligothiophenes (ST, 6T) were prepared on semiconductors (ZnSe, Si/SiO₂) by Knudsen evaporation. The orientation and order of these films were determined by FTIR spectroscopy. The dichroism of the (C=C) and (C-H)-stretching vibration demonstrates, that the films are highly orientated with a fixed tilt angle to the surface normal. This tilt angle y can be calculated from the dichroitic ratio of the polarized spectra. The order of these films was derived from the factor group splitting of the γ-C-H-out-of-plane mode. Vapor deposition on a substrate at 380 K results in a crystalline phase. A liquid crystal phase was obtained by evaporating on substrates at room temperature (300 K). In 30–100 nm films of 6T two different liquid crystalline phases were observed. By annealing 5T films the liquid crystal phase changes into the crystalline phase. After annealing 6T only the smectic phase was obtained. The intensity ratios of the factor group splitted bands give the herringbone angle τ.     

Modelling and simulation of bulk metallic glass production process with suction casting

Abstract

An integrated model, which coupled nucleation and crystalline growth with the heat transfer process, is presented in the present paper. The temperature, temperature gradient, cooling rate and the crystalline fraction of Zr₆₅Al_7·5Cu_17·5Ni₁₀ in suction casting have been calculated with this model. The results show that the metallic glass can be obtained at the bottom and the radial boundary of the rod sample, and that the crystalline phase precipitates in the centre of the sample. The crystalline fraction reaches the highest value of 0·0128 in the centre of the sample. Comparatively lower nucleation rate, as well as the higher viscosity and the cooling rate account for the formation of the bulk metallic glass.     

手性二糖对主链液晶聚合物性能的影响

采用溶液缩聚的方法,以6,6′-二羟基麦芽糖六乙酸酯(MA)、4,4′-对羟基联苯酚(MB)、癸二酰氯(SD)为单体,合成了主链液晶聚合物(P1～P7)。通过红外光谱(FT-IR),核磁共振谱(1H-NMR)、偏光显微分析(POM)、旋光性分析(SROT)、差示扫描量热(DSC)、X射线分析(XRD)等手段研究了手性单体对主链液晶聚合物性能的影响。研究表明,P1～P5呈现出近晶相的破碎焦锥织构,P6～P7呈现出胆甾相的彩色平面织构,手性基元的引入诱导出了胆甾相。液晶聚合物的玻璃化转变温度(Tg),熔点(Tm)和清亮点(Ti)随手性单体含量的增加而降低。     

手性近晶C相串型液晶共聚物的合成与性能

以对苯二甲酰氮,2,5－二[4-((S)-2-甲基丁氧基）苯甲酰氧基]对苯二酚和三缩四乙醇为单体,采用低温溶液缩聚的方法,合成了一系列新的手性近晶C相串型液晶共聚物。通过DCS,偏光显微镜,WAXD和旋光分析等方法,发现所有的手性共聚物都有光活性,当加热至熔融温度以上时形成近晶C相,共聚物的熔融温度（Tm)和各负同性温度（Ti)随共聚物分子中三缩四乙二醇用量的改变呈规律性变化。     

硅氧烷胆甾接枝聚合物液晶 PHECS 和 PHPCS 的红外光谱研究~*

利用变温红外(IR)光谱分析技术研究了硅氧烷胆甾接枝聚合物液晶 PHECS 和 PHPCS.PHECS 和 PHPCS 的 IR 光谱随其相态的转变而发生变化,分析了特征峰强度随温度的变化规律,讨论了聚合物的组成对形成液晶相和结晶相的作用。结果表明,液晶相和结晶相的不同在于胆甾基团的不同排列。     

Relationships between molecular structure and physical properties in bent-core mesogens

New five-ring bent-core mesogens that possess only ester connecting groups between the aromatic rings and different lateral substituents at the central phenyl ring are presented. The mesophases have been assigned by polarizing microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical measurements. It is shown that the mesophase behaviour depends strongly on the position of the lateral substituents. Compounds, which are derived from 4-cyano-, 4-chloro- and 4,6-dichloro-resorcinol, show polymorphism variants where polar phases (SmAP, SmCP) occur together with nematic and conventional smectic phases, e.g. SmA-SmAP, SmA-SmC(S)P(A)-Col(ob)-SmC(S)P(A), N-SmA-SmCP(A), SmA-SmC-SmCP(A) and SmC-SmCP(A). On the basis of the behaviour of two series of materials, the occurrence of different polar-switching mechanisms could be demonstrated. Apart from the usual mechanism by director rotation around the tilt cone, the polar switching can also take place through collective rotation of the molecules around their long axes, which corresponds to a field-induced switching of the layer chirality. A remarkable finding is the polar switching in the crystalline modification of long-chain, bent-core compounds with a methyl group in 2-position, which is accompanied by a clear change of the optical texture and by a relatively high switching polarization (approx. 600 nC cm(-2)). It was found for selected bent-core compounds that, above the transition temperature of a polar to a non-polar phase, the non-polar phase can be transformed to the polar phase by application of an electric field, which was proved for the transitions isotropic-SmCP(F), SmA-SmCP(F) and isotropic-CrII polar.     

含手性基元的侧链液晶聚合物的合成与性能表征

文中设计与合成了国内未见报道的单体M1、M2和系列手性液晶聚合物。通过差示扫描量热(DSC)、偏光显微分析(POM)、广角X射线衍射、旋光仪等测试手段研究了单体M1和手性液晶聚合物液晶性能。结果表明,M1为向列型液晶单体,M2为手性非液晶单体。聚合物P2~P4呈现近晶A相,P5,P6为胆甾相,P7的液晶性能已不明显,聚合物P8已没有液晶性能。具有宽的液晶相范围,液晶相范围均高于140℃。随着手性单体M2含量(0%~50%)的增加,聚合物的玻璃化转变温度、清亮点温度、液晶相范围均呈现降低趋势。     

Effect of water quenching and SiO2 addition during vitrification of fly ash Part 1: on the crystalline characteristics of slags

The objective of this study is to investigate how cooling rate and basicity in a vitrification process govern the crystalline characteristics of slags. In this experiment, the incineration fly ash mixtures with various SiO2 addition ratios were vitrified at 1450 degrees C and cooled down separately by air or water. Different thermal analysis, scanning electron microscopy and X-ray diffraction analysis with an internal standard addition were applied to investigate the crystalline characteristics of slags. The microanalytical mapping images showed that water quenching and the addition of SiO2, both enhanced the glassy amorphous phase to distribute more uniformly in slags. Addition of SiO2 would lower the melting temperature of fly ash mixtures and retard the formation of crystalline phases in slags. When the basicity (mass ratio of CaO to SiO2 before vitrification) was >0.990, the profiles of crystalline phases in slags with equal basicity were similar no matter how they were cooled. However, when the basicity <0.674, water quenching greatly enhanced the formation of the glassy amorphous phase in slags. For air cooled slags, an even lower basicity (<0.511) is required to vitrify fly ash well.     

Thermodynamic–kinetic model for the simulation of solidification in binary copper alloys and calculation of thermophysical properties

An earlier developed thermodynamic–kinetic solidification model for binary copper alloys is extended to take into account the formation of the bcc phase via the peritectic transformation and the formation of binary compounds from the fcc phase. Also the eutectic and eutectoid transformations are simulated but only approximately, by modeling the movement of the fcc/eutectic and fcc/eutectoid interfaces due to the diffusion kinetics of the fcc phase only. The new model can handle binary copper alloys containing solutes Ag, Al, Cr, Fe, Mg, Mn, Ni, P, Si, Sn, Te, Ti, Zn and Zr. Depending on the alloy composition, cooling rate and dendrite arm spacing, the model determines the fractions and compositions of the phases (liquid, fcc, bcc, compounds) and calculates thermophysical material properties (enthalpy, specific heat, thermal conductivity, density and liquid viscosity), needed in heat transfer models, from the liquid state down to room temperature. The model is applied to Cu–Sn and Cu–Zn alloys but also to some other binary alloys to show the effect of cooling on the phases formed. Depending on the alloy system, the solidification structures obtained after real cooling processes are shown to be quite different from those estimated from phase diagrams.     

Phases in Plasma Sprayed Thermal Barrier Coatings from Yttria Partially Stabilized Zirconia

The application of thermal barrier coatings (TBC) is increasing in aeroengines. Surface temperatures up to 1450°C require the application of ceramic TBCs because the temperature capability of metallic substrate materials is not high enough. The service life of turbine components could be improved by the use of yttria partially stabilized zirconia top coatings. The most successfull TBCs are made from 7–9 wt‐% yttria partially stabilized zirconia. One of the most discussed reasons of damages of such TBCs is the transformation between monoclinic and tetragonal phase in zirconia in connection with a dramatic change in volume. Thus in this work resulting phases of plasma sprayed zirconia coatings were investigated. It was found that no monoclinic phase could be detected after heat treatments at 1300, 1400 and 1466°C with cooling rates > 2°/min. Only with cooling rates < 2°/min monoclinic phases occured. It can be concluded that the metastable tetragonal high temperature configuration of yttria partially stabilized zirconia is “very stable”. The conditions in aeroengines with cooling rates > 2°C prevent the formation of the monoclinic phase in zirconia.