Orientation of Thermotropic Liquid-Crystalline Polyesters in High Magnetic Fields

Strongly oriented poly-crystalline samples of polyesters containing mesogenic moieties and flexible spacers in the main chain have been produced by slowly cooling the molten samples in magnetic fields of up to 16 Tesla. This simple method appears to be successful for those polymers forming a “true” nematic phase over an extended range of temperatures. Cholesteric polymers are not oriented. Mesogenic polymers (such as SEB-5, SUC-5, and SEB-7) which pass only through a state of partial parallel ordering of chain segments before cystallizing cannot be oriented macroscopically. In these samples crystallization may interfere with the chain alignment in the magnetic field. In contrast to low molecular weight liquid crystals, the isotropic-liquid crystalline transition of the polyesters investigated has a strong thermal hysteresis.     

Phase Diagrams of Cholesteric and Nematic Thermotropic Liquid-Crystalline Polymers

Linear mesogenic polyesters with flexible spacers (molecular weight ranging from 9,000 to 20,000) are studied by polarized microscopy. The nematic and cholesteric mesophases are identified by means of the contact method. Two enantiomers form perfect solid, cholesteric and liquid solutions. The sign of the twist of the cholesteric phases are determines.     

Monte Carlo Simulation of the Liquid-Crystalline Ordering of Semiflexible Polymers

We present results from Monte Carlo simulations of the liquid-crystalline ordering in the athermal systems of partially flexible polymers in a two- and three-dimensional continuum. Any two non-bonded chain monomers interact via a hard spher potential. The chains are placed in a periodic box consistent with the number density C. It is observed that the mean dimensions of chains and the orientational order parameters increase sharply with increasing C. In other words, we observe elongation and stiffening of the chains. In contrast to semiflexible polymers, the mean dimensions of flexible chains are reduced as the density is increased.     

Liquid-Crystalline Solvents as Mechanistic Probes. 10. Dynamics of Intramolecular Quenching of Pyrenyl Fluorescence in the Liquid-Crystalline and Isotropic Phases of a Cholesteric Solvent1

Abstract

The effect of cholesteric order in a 59.5/15.6/24.9 (w/w/w) mixture of cholesteryl oleate/cholesteryl nonanoate/cholesteryl chloride (CM) on the intramolecular fluorescence quenching of l,3-bis(l-pyrenyl) propane (P3P) has been explored. A comparison with fluorescence quenching of N,N-dimethyl-4-[3-(l-pyrenyl)propyl]aniline (P3D) in CM is made. From the Arrhenius activation parameters for quenching in the cholesteric and isotropic phases, it is concluded that the motions which take the ground state conformers of P3P to their quenching transition state are nearly impervious to macroscopic CM mesophase order: in the cholesteric phase, E'_a = 10.5±0.4 kcal mol^?1 and ΔS^? = 1 ± 1 eu; in the isotropic phase, E'_a = 10.0 ± 0.2 kcal mol^?1 and ΔS^? = 0 ± 0.5 eu. An explanation of these results is advanced.     

Calorimetric Study of Crystalline and Liquid-Crystalline Polymorphism in the Homologues of Terephthal-bis-n-alkylaniline

The phase sequences of the homologues with n (the number of carbon atoms in the terminal alkyl chains) from 2 to 8 are obtained. At low temperatures, i) several crystalline modifications are found in each of the members with n = 4, 5, and 6 and ii) the monotropic transitions between crystal and smectic phase are observed in almost all the members. At intermediate temperature, iii) between the smectic H and C phases, the smectic F phase is found in the homologues with n ≥ = 5 by morphological observation or by a rheological method. The constancy of the temperature of the S_H(or S_F) – S_c transition with respect to “and broadening of the temperature range of S_H with increasing n in the expense of nematic phase are worthy of note. The even-odd effect of the end chain length n is observed very distinctively on the crystal melting and clearing point. Proton NMR measurement reveals a large mobility in the terminal alkyl chains in the crystal of the member with n = 6.     

Thermotropic Poly(Ester-Amides) Based on Naphthalene Monomers

The structure and properties of a range of thermotropic poly(ester-amides) derived from 2,6-naphthalene derivatives is described. Many of these polymers may be melt-processed into fibers, monofils, and molded structures having very attractive physical and mechanical properties. A variety of monomers has been used and structure/composition/property relationships are described along with details of synthesis and processing conditions. Both fibers and molded articles may be heat-treated to enhance their tensile properties. Molded articles and extruded rods have exceptional tensile moduli in the unfilled state.     

Fabrication of Pre-tilted Vertical Alignment Layers for High-Speed Liquid Crystal Display Using Bi-functional Photoreactive Monomers

Abstract

To enable recent 3D and moving picture applications, liquid crystal displays (LCD) must exhibit fast response and wide viewing angle characteristics. Pre-tilted vertical alignment layers for high-speed LCD were fabricated using bi-functional photoreactive monomers. The monomers can be confined to the polyimide layer and photo-polymerized by UV exposure under voltage. Response characteristics of photo-controlled alignment films according to the structure were investigated. Vertical alignment properties were evaluated using a polarizing optical microscope, and electro-optical characteristics were compared through the voltage-transmittance curve and response time measurement. Faster response speed could be obtained by using photoreactive monomers having a long alkyl chain.     

菱镁矿悬浮态与堆积态煅烧对产物特性的影响

利用实验室自制小型模拟悬浮态煅烧装置和马弗炉,对菱镁矿进行快速煅烧试验制备轻烧氧化镁,分别对悬浮态和堆积态的煅烧产物进行分解率、XRD、SEM、活性等分析,探讨两种煅烧方式对轻烧氧化镁特性的影响.结果表明:相对于堆积态煅烧,菱镁矿经悬浮态煅烧1 min后分解率即可达到98;以上,得到的轻烧氧化镁晶粒尺寸小、结晶度低,比表面积大、表现出很高的活性;悬浮态煅烧显著强化了热传递过程,加快了反应速度,生产效率成倍提高,产品性能好、质量稳定,可应用于大规模生产高活性轻烧氧化镁.     

Solid State Behaviour of Vinyl Quinones

Abstract

2,5-Bisvinyl-1,4-benzoquinones 1 and 2-vinyl-1,4-bsnzoquinones 2 substituted with aryl or ester end groups have been synthesized. The 2,5-bisstyryl-1,4-benzoquinones 1 (R=phenyl, p-tolyl, o-tolyl) crystallize with a 7 Å-stacking axis. But only for the o-tolyl derivative the contacts between the vinyl groups are close enough to allow a four-center type photopolymerization. The ester derivative 1 (R=COOEt) has a layer structure and can be photooligomerized in the crystal. The generated cyclobutane subgroups have twofold symmetry. The vinylquinones 2 (R=aryl) may be dimerized photochemically in the crystal at the vinyl groups to centrosymmetric cyclobutanes. Crystals with 4 Å stacking axis are also photoreactive.     

光子晶体多组元缺陷态问题研究

缺陷态光子晶体可以用于制作良好的谐振器、偏振器、滤光器等光学器件,具有重要的应用价值。本文发展了光子晶体缺陷态问题的PG有限元界面问题计算方法,有效地处理了各种不同组元体系、几何结构、界面形状、材料属性以及模态的光子晶体缺陷态问题。数值结果表明,二组元结构单点缺陷对带隙的影响较小,只是使局部范围内的波继续传播而产生一条缺陷带,多点缺陷使一些特定范围内的波可以传播而产生多条缺陷带,线缺陷产生的影响较大,可以使整个禁带消失。结合线缺陷与点缺陷,波导结构中的侧点缺陷可以有效地应用于光子晶体阻带内诱导窄通带或在波导的通带内诱导非常窄的阻带。三组元结构引入了不均匀介质、复杂介质形状以及不同几何结构的缺陷态。通过计算与分析发现Ω₃区域的介质形状对结果影响比较有限,表面层越不光滑禁带越窄,n型缺陷态在TM模中的高频区域更容易产生禁带。对于TE模来说,n型与v型的缺陷态更容易产生禁带。     

The Triplet State in Pyrene

Both emission and excitation spectra of phosphorescence and delayed fluorescence of pyrene single crystals have been investigated between 2 K and 300 K using cw dye laser excitation. The experiments prove that the lowest triplet state is excitonic in nature in the high and low temperature crystalline phases. No evidence for triplet excimer emission could be found. The so-called regular broad band triplet excimer emission was spectrally resolved at low temperature and identified as trap emission. On the basis of polarized high resolution excitation spectra of undoped normal and perdeuterated pyrene (supplemented by Zeeman spectra at helium temperature) and the concentration dependent phosphorescence excitation spectra of isotopically mixed crystals the triplet state symmetry and the excitonic Davydov splitting of the low temperature crystalline phase was determined. The resonance pair interaction between the dimer molecules was found to be an order of magnitude smaller than predicted from calculations reported so far.     

To the Unified Model of Condensed State

The problem of unified model of condensed state can be solved by using solid-like model of liquids. A liquid arises when in a heated crystal a universal process of microcrack formation takes place that leads to originating a great number of very small crystals: microcrystallites. In the paper the two basic notions: the effective temperature of crystal surfaces and the internal thermal stresses in crystals are discussed. These notions make possible the microcrystallite model of liquids and the unified model of condensed state. Thus, the microcracks, resulted from thermal stresses, below the melting point lead only to decreased strength of crystals but above melting point the microcracks are spread all over the crystal bulk and cause splitting of the crystal into microcrystallites that are moving freely, in short, making up a liquid. The simple relations for these processes are given. In the end of the paper the identical features of the condensed states, solid and liquid, has been considered.     

State of Order in Liquid Crystalline Elastomers

The orientation behavior of crosslinked liquid crystal-line side chain polymers is determined by IR-dichroism measurements. In stretched samples the conformation of the polymer main chain and the chemical constitution of the rodlike side chain determine the position of the director in relation to the axis of stress. The order parameter S has the same temperature dependence and is of the same magnitude as in the corresponding uncrosslinked liquid crystalline polymers. The order parameter and the nematic to isotropic phase transformation temperature are independent of the applied mechanical stress under the experimental conditions (elongation up to 50%).     

AFM in Organic Solid State Reactions

Abstract

Organic solid-state reactions are probed with the atomic force microscope (AFM). In all cases phase rebuilding gives rise to characteristic submicroscopic features which change in shape due to phase transformation in later stages of the chemical reaction. Photo-(E/Z)-isomerization of olefin 1 occurs in the crystal, photodimerization of 9-chloroanthracene 3 is used as a probe for characterizing the luminosity distribution of SNOM-tips. Gas/solid imbibition in chiral host 5 proceeds enantiospecifically. Histidine crystals form the dihydrochloride with HC1, ammonia and methylamine react face-selectively with crystalline adipic acid 8, furane-2-carboxylic acid 10 and 2-mercaptobenzothiazole 12. Crystals of olefin 14 add chlorine. Solid-state diazotations and subsequent transformations of the solid diazonium nitrates into triazenes occur quantitatively. Solid/solid pinacol- and benzilic acid rearrangements are probed with the AFM. The features formed by long range molecular movements relate to the crystal packing and are thus different on different faces. Correlations with X-ray structural data are demonstrated. All reactions proceed to completion on a preparative scale and do not produce wastes as do their less selective counterparts if performed in solution.     

Orientation of Alkoxybenzoic Acids in Their Nematic State

While studying the polymerization of various monomers within mesophases of alkoxybenzoic acids we have observed the formation of order in the oc-tyloxybenzoic acid in its nematic state. We would like to report here briefly our preliminary findings.     

Solid State Dimerization of a 5-Vinylidene- Cyclopentadiene

Abstract

The kinetically stabilized 1.3-di-t-butyl-5-vinylidenecyclopentadiene (1) dimerizes in a thermal solid state reaction to the tetraquinane derivative 6. A reaction mechanism for this topochemically controlled reaction is proposed on the basis of results of X-ray analyses and semiempirical calculations.     

Solid State Structures of Anhydrous 1-Aminoethylidenediphosphonic Acid

Abstract  

The 1-aminoethylidenediphosphonic acid (AEDPH₄) is anhydrous when it is synthesized according to the U.S. Patent 4239695. It crystallizes in water to form hydrous crystal AEDPH₃·H₃O (1). With the help of a simple low-temperature, low-pressure hydrothermal method and template 2,2′-bidpyridyl (2,2′-bipy), single crystals with the same structure of the anhydrous AEDPH₄ (2) is obtained. Compound 2 were characterized by elemental analysis (EA), infrared spectrometry (IR), thermogravimetric analysis (TGA) and X-ray single crystal diffraction. In compounds 2, the AEDPH₄ molecules are linked into 3D supramolecules by various hydrogen bonds.