Anticlinic smectic C phase in new and novel five-ring hockey stick-shaped compounds

The synthesis of a new homologous series of novel five-ring compounds composed of hockey stick-shaped molecules derived from 4-hydroxybiphenyl-3-carboxylic acid which exhibit an interesting sequence of phase transitions is presented. Uniaxial nematic and smectic A phases, anticlinic smectic C phase and an unidentified smectic phase at a lower temperature than the latter have been observed. This is perhaps the first example of hockey stick-shaped compounds exhibiting anticlinic smectic C phase directly from the isotropic phase. Polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction measurements and electro-optical switching studies were carried out to identify the mesophases.     

Synthesis and liquid crystalline investigation of chiral 6-alkoxy-2-naphathoic acid derivatives

A two new series of materials with a chiral fragment derived from ((S)-(─)-2-methyl-1-butanol and 6-alkoxy-2-naphathoic acid as the molecular core was synthesised and investigated. All the homologues exhibited enantiotropic mesomorphism. Chiral smectic C (SmC*), smectic A (SmA) and chiral nematic (N*) phases were observed in different homologues. All the compounds were characterised by spectroscopic and elemental analysis. Thermal investigations and mesophase characterisations for all the compounds were carried out by the combination of DSC and POM analysis. The effects of the central linkage and various terminal normal alkyl chains with its structurally related compounds have been discussed.     

The influence of flexible spacer and the chirality of the core on the formation of chiral nematic phase of symmetric dimers containing trifluoromethyl terminal

Seven symmetric liquid crystal (LC) dimers containing different chiral cores and LC arms have been synthesised, termed EPDA-(R,S)PD, TFBDA-(R,S)PD, TFBA-(R,S)PD, TFBDA-(R)PD, TFBA-(R)PD, TFBDA-IB and TFBA-IB, respectively. TFBDA-(R,S)PD, TFBA-(R,S)PD, TFBDA-(R)PD and TFBDA-IB displayed chiral smectic A (SmA*) phase, while EPDA-(R,S)PD, TFBA-(R)PD and TFBA-IB exhibited chiral nematic (N*) phase. The effects of flexible spacer, structural type of LC arms and the chirality of the cores on the thermal properties of the dimers and the formation of N* phase have been studied. The results indicated that the chiral core was prone to induce the N* phase in LC dimer that contained nematic arms although the chirality of the core is very weak, while for the smectic LC arms containing CF3 terminal, the removal of the flexible spacer between chiral core and rigid LC units was conducive to the formation of N* phase. For example, TFBDA-(R)PD and TFBDA-IB displayed SmA* phase, while TFBA-(R)PD and TFBA-IB exhibited N* phase. However TFBA-(R,S)PD did not display N* phase, which reminded us that the chirality of the core and the conformation of the dimer also played an influence in the formation of the LC phase.     

Isotactic polystyrene/cis-decaline mixtures: phase diagram and molecular structures

Organized structures grown from iPS/cis-decalin solutions (ranging from 5% to 50% w/w) have been studied by several techniques. From DSC experiments the thermal behavior has been investigated as a function of the annealing temperature. The temperature-concentration phase diagram has been established. From neutron diffraction experiments the short range molecular order has been determined. We show that between the gel state formed at high undercooling and the crystalline state obtained at low undercooling there exist two intermediate phases: thes-phase, already described by Klein et al., and thep-phase. Except for the crystalline state all the other phases contain intercalated solvent molecules. Thegel state displays nematic-like order, whereas thes-phase is reminiscent of smectic arrangements. Thep-phase is less solvated and can be described as a peritectic system. Preliminary neutron scattering experiments show that chain-folding reappears in thes-phase, whereas it was shown to be absent in thegel phase.Formerly Laboratoire de Spectrométrie et d'imagerie Ultrasonores     

新型含氧亚甲基和亚胺桥键的液晶化合物的合成及介晶性

报道一类新的、结构通式为MeO₂CC₆H₄CH₂OC₆H₄CH＝NC₆H₄Y, Y＝OC_nH_2n＋1, Me, Cl, Br, NO₂, H 的棒状液晶化合物的合成. 通过DSC和偏光显微镜对其介晶性研究发现, 除Y＝H外, 这些化合物均具有介晶性. 当Y为非烷氧基时, 呈向列相液晶; 当Y为较短的烷氧基时(n＝1～3), 液晶化合物具有向列相(N); Y为较长烷氧基时(n＝4～16 ), 液晶化合物只有近晶B相(S_B)和近晶A相(S_A); S_A-I相变的熵变随烷氧链原子数而奇-偶变化, 但与N-I相变的“奇-偶效应”相反.     

Oligo (p -phenylene)s substituted with long alkoxy chains I. Thermotropic liquid crystalline properties and UV absorption/emission characteristics

A series of linear oligo (p-phenylene)s containing three, five and seven phenylene groups, modified with short lateral and long terminal alkoxy chains, were synthesized via Palladium complex-catalysed cross-coupling reactions. The thermotropic liquid crystalline and UV absorption/emission properties of these compounds were studied. It was observed that tri (p -phenylene)s develop a rich mesomorphism including tilted smectic type mesophases (SmC and SmF/SmI) and the nematic phase, whereas penta- and hepta-(p-phenylene)s substituted with short lateral chains develop only the nematic phase. From these observations it is clear that the short lateral chains hinder the layered molecular packing typical of smectic phases and promote the formation of the less ordered liquid-like nematic phase. Mesophases appeared at lower temperatures when longer end chains were used. The optical properties studied by UV-Vis and emission spectroscopy indicate that these systems are promising candidates for blue-emitting layers in electroluminescent devices.     

Rubidium and lithium butanoates binary phase diagram

The temperature and enthalpy vs. composition diagrams of the binary system [xC₃H₇CO₂Li+(1–x)C₃H₇CO₂Rb], where x=mole fraction, were determined by differential scanning calorimetry (DSC). This binary systems displays the formation of two mixed salts with a composition 1:1 and 1:2, which melt incongruently at T _fus=590.5 K, with Δ_fus H _m=11.6 kJ mol^–1, and congruently at T _fus=614.5 K, with Δ_fus H _m=20.2 kJ mol^–1, respectively. The phase diagram also presents an ionic liquid-crystalline phase in a wide temperature range: 95 K.     

New symmetric azobenzene molecules of varied central cores: Synthesis and characterisation for liquid crystalline properties

A new series of azobenezene liquid crystals (LCs) was designed and synthesised by known and straightforward methods. The central connecting cores of the molecules varied viz., benzene/naphthalene/biphenyl. The molecular structures were confirmed by infrared, UV, nuclear magnetic resonance spectroscopic techniques. The LC texture and thermal phase behaviours were investigated by polarising optical microscopy and differential scanning calorimetry. Smectic B phase was found in biphenyl-derived azobenzene ester. The effect of central core on LC properties was investigated. The decreased angle at central connecting core suppressed the melting points, phase transition temperatures without losing LC properties, whereas, in moderate angle compounds LC properties were suppressed. The compounds with increased angle at central core favours rich mesomorphism.     

新型三噻吩衍生物的合成及其液晶性能

近晶A相;新型三噻吩衍生物的合成及其液晶性能     

有玻璃态和液晶态的胆甾烯基苯并菲的合成及介晶性

将盘状液晶基元苯并菲与手性向列型液晶基元胆甾烯基结合的化合物, 可望出现全新的性质. 合成了含有胆甾烯基的苯并菲化合物C₁₈H₆(OC₅H₁₁)₅(OC₅H₁₀COOCh) (2), 2,7-C₁₈H₆(OC₅H₁₁)₄(OC₅H₁₀COOCh)₂ (4), C₁₈H₆(OR)₃(OC_nH_{2nCOO- Ch)3 (R＝C5H11, C7H15, C9H19, C11H23, n＝1, 5, 10) (6a～6f), C18H6(OC5H10COOCh)6 (Ch: cholesteryl) (8). 偏光显微镜和差示扫描量热法对这些化合物的热致介晶性研究结果显示, 化合物 4, 6a～6e具有手性盘状向列相和玻璃态, 8呈现近晶B相(SB)和玻璃态. 随间隔基长度n和烷基链R碳原子数的增加, 化合物玻璃化温度和清亮点呈下降趋势. 随着胆甾烯基数目减少, 化合物的玻璃化温度和清亮点降低.}     

Thermal tuning band gap in cholesteric liquid crystals

The phase of a liquid crystal (LC) changing from a nematic phase to a cholesteric (Ch) mesophase is achieved by adding different ratios of chiral dopants S811. By studying the transmission spectrum, we are able to measure the helical pitch in cholesteric phase. The pitch in the mixtures of nematic E7 and chiral dopants S811 as a function of the concentration of the dopant and temperature is investigated. The sensitivity of the selective reflection notch of the cholesteric phase to the thermal tuning depends strongly on the ratios of the chiral dopants. It reveals that the influence of temperature is more profound for those cholesteric liquid crystals (CLCs) which exhibit smectic A (SmA) at lower temperatures. When fitted using Keating's formula, the helical pitch calculated from our experimental results lies on the predicted curve. Optimised ratios of the mixture CLCs for the optimised reflection band with the specified wavelength ranging from 467 nm to 2123 nm are suggested.     

Synthesis of novel nematic liquid crystals containing 3,3'-dimethyl-2,2'-bipyridyl

Liquid-crystalline 3,3′-dimethyl-2,2′-bipyridyl derivatives with long 4-(alkoxyphenyl)ethynyl (-C≡C-C₆H₄-OR) groups in the 5,5′-positions were synthesized by palladium-catalysed crosscoupling reactions. The compounds exhibit exclusively nematic behaviour; for example, the hexyl derivative showed a nematic phase over the temperature range 145.2–205.0°C. On increasing the length of the terminal chain, the transition temperatures were lowered; for example, the hexadecyl derivative was nematic in the range 117.0–126.8°C.     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

Flexible taper-shaped liquid crystal trimer exhibiting a modulated smectic phase

We prepared some taper-shaped liquid-crystalline trimers in which two phenylpyrimidine units and a 1,4-diphenyl-2,3-difluorobenzene unit are connected to 2,4-dihdroxy benzoic acid via flexible spacers. We then investigated their liquid-crystalline properties using polarised optical microscopy, differential scanning microscopy and X-ray diffraction. 6-[4–(5-Octylpyrimidin-2-yl)phenyloxy]hexyl 2-{7-{4-[4–(4-hexylphenyl)-2,3-difluorophenyl]phenyloxy}heptanoyloxy}-4-{6-[4–(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy}benzoate (1) was found to exhibit a phase sequence of isotropic liquid – nematic – intercalated smectic A – intercalated anticlinic smectic C – modulated smectic C. The structure–property relation in the taper-shaped trimers reveals that the modulated phase is induced by competition between an intercalated structure stabilised by dipole–dipole interaction and a monolayer structure by packing entropy effects. Conformational change of compound 1 induced by intermolecular interactions plays an important role in the phase transition behaviour.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

氢键缔合主链超分子液晶聚合物:间隔基及扩展介晶元长度的影响研究

采用慢挥发溶剂组装方法制备了一系列羧酸/吡啶氢键缔合的主链型超分子复合物,并采用FTIR,DSC以及偏光显微镜等对其相转变与热致液晶相行为进行了比较研究.研究表明,分别具有较短的6或10个亚甲基的烷烃间隔基的双苯甲酸衍生物4',4'-二羧酸-1,6-二酚氧基己烷(C6-2COOH)和4',4'-二羧酸-1,10-二酚氧基癸烷(C10-2COOH)的系列复合物具有较高的熔点和清亮点,一般都只出现结晶近晶相和多晶型转变现象.而具有柔顺性较好的四甘醇醚链间隔基的4,4'-二羧酸-α,ω-二酚氧基四甘醇醚(C8O4-2COOH)得到的系列复合物均在降温过程生成单致的流体近晶SA和/或向列N液晶相.可见,间隔基增长,相转变温度降低,最终导致真正的流体液晶相的产生.另一方面,对于从同一种二元羧酸得到的组装体系,从4,4'-联吡啶(4,4'-BPy)、4,4'-联吡啶乙烯撑(4,4'-BPyE)到对苯二酚二异烟酸酯(p-PhBPy),由于双键或酯基的引入,可变形性和极性增大,刚性依次减弱,尽管中心核部分持续长度增大,所得复合物的各向同性化温度降低,形成流体液晶相的趋势增强,液晶有序性降低,流动性增加.指出了早期文献报道的一些不一致甚至矛盾的结果.通过不同系列的对比研究,得出的一些规律性对氢键组装尤其对羧基/吡啶氢键缔合超分子体系设计与构筑具有一定指导意义.     

Thermal,morphology, and NMR characterizations on phase behavior and miscibility in blends of isotactic polystyrene with poly(cyclohexyl methacrylate)

The miscibility and phase behavior in a binary blend of isotactic polystyrene (iPS) and poly(cyclohexyl methacrylate) (PCHMA) were investigated by differential scanning calorimetry, optical microscopy (OM), and solid‐state ¹³C cross‐polarity/magic‐angle spinning NMR. The iPS/PCHMA blend was miscible when all compositions showed a single composition‐dependent glass‐transition temperature (T_g) and when the blend went through a thermodynamic phase transition upon heating to above the lower critical solution temperature as determined by OM measurements. The ¹H NMR spin‐relaxation times in the laboratory frame (T) and in the rotating frame (T) for iPS/PCHMA blends with various compositions and neat components were directly measured through solid‐state¹³C NMR. The results of T indicated that the blends are homogeneous, at least on a scale of 75–85 nm, confirming the miscibility of the system. The single decay and composition‐dependent T values for each blend further demonstrated the blends are homogeneous on a scale of 2.5–3.5 nm. The results suggested that iPS and PCHMA are intimately mixed at the molecular level within the blends at all compositions. The tacticity of polystyrene does not seem to adversely influence the miscibility in blends of iPS/PCHMA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 772–784, 2003     

Cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase

ABSTRACT

The synthesis and characterisation of several members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkane (CBnCB) and the 1-(4-cyanobiphenyl-4′-yloxy)-ω-(4-cyanobiphenyl-4′-yl) alkane (CBnOCB) homologous series are reported. The new odd members described CB5CB, CB13CB, CB4OCB, CB8OCB and CB10OCB all exhibit twist-bend nematic and nematic phases. The members of these series already reported in literature, CB7CB, CB9CB, CB11CB and CB6OCB, were also prepared in order to allow for a direct comparison of their transitional properties. The properties of these dimers are also compared to those of the corresponding members of the 1,ω-bis(4-cyanobiphenyl-4,-yloxy) alkanes (CBOnOCB). For any given total spacer length, for odd members of these series, the nematic–isotropic transition temperatures and associated entropy changes are greatest for the CBOnOCB dimer and lowest for the CBnCB dimer. These trends are understood in terms of molecular shape. For short spacer lengths, the twist-bend nematic–nematic transition temperature (T_NTBN) is higher for the CBnOCB series than for the CBnCB series but this is reversed as the spacer length increases. Of the CBOnOCB dimers, a virtual value of T_NTBN was estimated for CBO3OCB and T_NTBN was measured for CBO5OCB. These values are considerably lower than those observed for the corresponding members of the CBnCB or CBnOCB series. The dependence of T_NTBN on molecular structure is discussed not only in terms of the molecular curvature but also in the ability of the molecules to pack efficiently. As the temperature range of the preceding nematic phase increases, so the twist-bend nematic–nematic transition entropy change decreases and the transition approaches second order for the longer spacers. For comparative purposes, the transitional behaviour of the even-membered dimers CB6CB, CB5OCB and CBO4OCB is reported and differences accounted for in terms of molecular shape.     

Competition between micro-segregation and anti-parallel alignment of an amphiphilic rod-like liquid crystal

Recently, we reported that a rod-like molecule, 4-[4-(7-hydroxyheptyloxy)phenyl]-1-(4-hexylphenyl)-2,3-difluorobenzene, exhibited a nematic phase with a layered structure and smectic C phases consisting of three states. We prepared a homologous series of the rod-like molecules in which a 2,3-difluoro-1,4-diphenylbenzene unit and a hydroxyl unit are connected via a flexible methylene spacer. We investigated their physical properties using polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Although they showed nematic, smectic A and smectic C phases, the phase structures were found to depend on the flexible spacer length. Those compounds possessing a shorter spacer length than a heptyl unit exhibited bilayered smectic A and smectic C phases, whereas those possessing a longer spacer length than a heptyl unit showed conventional monolayered smectic A and smectic C phases. A nematic phase with a smectic-like layer ordering was observed for the compound possessing an octyl unit. The structure–property relations of the amphiphilic compounds are discussed.