Study of the liquid crystalline phases of benzopurpurin in water

We report the NMR study of the liquid crystalline phases of aqueous solutions of the dye benzopurpurin (BP-4B). Upon changing dye concentration, the system exhibits a phase transition between two ordered phases at about 3·5 wt %. The structure of these phases was not determined but the evidence suggests that they consist of columns or helically twisted columns of stacked dye molecules which are randomly oriented, similar to nematic phases.     

Characteristics and self‐assembly behaviors of photochromic triblock azo‐copolymers based on hard‐soft‐hard segments synthesized via RAFT process

A novel series of hard‐soft‐hard triblock azo‐copolymers (TBCs) composed of poly(2‐[2‐(4‐cyano‐azobenzene‐4‐oxy)ethylene‐oxy]ethyl methacrylate) (PCEAMA), poly(methyl methacrylate) (PMMA) and poly(p‐dodecylphenyl‐N‐acrylamide) (PDOPAM) were synthesized by employing reversible addition‐fragmentation chain transfer polymerization. Chemical structures and molecular weights were characterized by ¹H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Thermal behavior, mesophase, photochemistry and morphology were investigated using differential scanning calorimetry (DSC), optical polarizing microscopy (OPM), ultraviolet–visible spectrophotometry (UV–vis), atomic force microscopy (AFM) and grazing‐incidence small‐angle X‐ray scattering (GISAXS). Kinetic studies confirmed characteristic of controlled/living radical polymerization with low polydispersities (≤1.40). TBCs manifested both endothermic and exothermic transition peaks assigned to smectic to nematic, nematic to smectic, and smectic‐A to smectic‐C phases. TBCs having hight azo fractions of 39 and 34 wt % revealed textures of smectic phase whereas TBC possessing 30 wt % of azo content exhibited poor texture, suggesting nematic phase. Regarding TBC with low azo ratio (25 wt %), neither mesophase texture was found. All TBCs showed photoresponsive behavior under UV–vis irradiation or thermal relaxation. TBC‐1 with PCAEMA (39 wt %), PMMA (40 wt %) and PDOPAM (21 wt %) generated a mixture of cylinder and lamellar nanostructures compared to TBC‐2 and TBC‐3 which formed lamellae. However, TBC‐4 having the highest PDOPAM fraction (50 wt %) produced hexagonal cylindrical nanostructure. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1617–1629     

An X-ray diffraction study of the different nematic mesophases of liquid-crystalline poly(urethane-ester)s

An x-ray investigation on powder specimens and stretched oriented fibers of poly(urethaneester)s TDI-CmCn, derived from various mesogenic alkylene di[4-(ω-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn; m = 2, 4, or 6, and n = 4, 6, 8, or 10) and 2, 4-toluenediisocyanate (TDI), is reported. Evidence is provided for the formation of two different nematic mesophases in the polymers, namely a cybotactic nematic and a conventional nematic mesophase. Whereas samples TDI-C2C6, TDI-C6C4, and TDI-C6C10 formed one cybotactic nematic mesophase, samples TDI-C4C6, TDI-C6C6, and TDI-C6C8 exhibited both cybotactic nematic and conventional nematic mesophases in a sequence with increasing temperature, which were connected by a first-order transition. The analysis of the various features of the small-angle x-ray diffraction patterns indicates that two structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophase of these poly(urethane-ester)s. © 1995 John Wiley & Sons, Inc.     

The phase diagram of the lyotropic nematic mesophase in the TTAB/NaBr/water system

The phase diagram of the nematic mesophase present in the tetradecyltrimethylammonium bromide/sodium bromide/water ternary system was determined. A calamitic nematic mesophase (N_C) was observed which extends to very high concentrations of electrolyte. The order parameters of the surfactant head group in the mesophases were studied by the NMR quadrupolar splitting of the deuterated surfactant. On increasing the temperature of nematic mesophases with low electrolyte concentrations, a phase separation occurs with the formation of a more highly ordered hexagonal phase and an isotropic phase. Diffusion measurements of the isotropic micellar solution by the NMR PFG method were used to estimate hydrodynamic radii at low surfactant concentrations and to study micelle diffusion as the concentration of the surfactant was increased to the liquid crystalline region. At higher surfactant concentrations, the diffusion coefficient reached a limiting value. The calamitic nematic mesophase in this surfactant/electrolyte/water system appears to be formed by long wormlike micelles.     

聚对苯甲酰胺液晶态球晶生长机理

本文用热台偏光显微镜和透射电子显微镜研究了聚对苯甲酰胺(PBA)/H_2SO_4液晶态生长球晶的形态结构和结晶机理。结果表明,PBA/H_2SO_4向列型液晶相具有过冷状态,可达30—40℃左右,并可生长球晶结构,一般直径可达5毫米左右。20Wt％溶液在不同的过冷态结晶时,可以生成三种形态的球晶结构,这是由于构成球晶的基本结构单元——有序微区结构在不同过冷条件下堆砌排列的规整程度不同的缘故。球晶的形态结构只与过冷程度有关,而与溶液的浓度无关。同时还研究了变温和剪切应力下结晶的球晶形态。     

The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethaneester)s

The peculiar liquid crystalline behavior of two poly(urethane-ester)s TDI-C6C4 and TDI-C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI-C6C8 and of one cybotactic nematic mesophase in TDI-C6C4. IR spectroscopy indicates that different hydrogen bonded and non-bonded structures occur with varying temperature. The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic-mechanical behavior of these poly(urethane-ester)s which is similar to the one of slightly crosslinked thermoreversible networks.     

Effect of salt on the phase diagrams of two binary lyotropic liquid crystalline solutions

The effect of adding salts NH₄OH and CsOH to aqueous solutions of NH₄PFO and CsPFO, respectively, was studied for concentrations in the range 0 to 2 wt %. In both systems, the isotropic to nematic and nematic to lamellar phase transition temperatures were elevated. There was an insignificant effect on the width of the nematic range in the NH₄PFO system, while the nematic phase was widened by as much as ∼3°C in the case of CsPFO. High-resolution X-ray scattering measurements were performed to determine the micellar size and its dependence on temperature for 52 wt % NH₄PFO solution in water.     

Optical Properties and Photopolymerization of Liquid Crystalline (Acetyl) (Ethyl) Cellulose/Acrylic Acid System

The structure and properties of a chiral nematic phase, which reflects one hand of circularly polarized light in a narrow region of wavelength, of fully acetylated (ethyl) cellulose [(acetyl) (ethyl) cellulose, AEC] in acrylic acid (AA) were studied in comparison with (ethyl) cellulose (EC). AEC mesophase formed right-handed chiral nematic structure while EC formed left-handed one. AEC mesophase showed higher birefringence and reflection intensity. The relationship between the reflection wavelength and the polymer concentration was negatively correlated for both AEC and EC mesophases. The relationship between the reflection wavelength and the molecular weight was also negative for AEC mesophase whereas positive for EC mesophase. AEC mesophase was solidified by photopolymerization of AA moiety. It was revealed that the optical properties of AEC mesophase could be preserved by photopolymerization, since the resulting solid material reflects selectively one hand of circularly polarized light.     

Thermotropic homopolyesters. IV. Study of fiber formation

We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun from both the nematic and smectic phases of these semiflexible chain polymers were poor. Increasing the polymer molecular weight or extrusion rate only afforded a modest improvement in fiber properties. Most polymers could not be spun at temperatures corresponding to the existence of the single mesophase. Hence the low viscosity typical of the nematic mesophase is not necessarily an advantage in fiber formation from the melt. It appears from these results that this type of polyester does not possess adequate chain extension to develop ultrahigh-modulus properties. The director, which describes the local orientation of molecules within the mesophase, may undergo more frequent variations than is the case for rigid chain polyesters. Mechanisms relevant to flexible polymers may contribute to the development of orientation for this class of nematogenic melts.     

Preliminary communication Electro-optical properties of benzyl fluoroalkyl ether derivatives

Several new fluorinated liquid crystal compounds, 4- n -propylbicyclohexylbenzyl fluoroalkyl ethers (C2BFE) and a 4- n -propylcyclohexylbenzyl 2-perfluoropropoxy-2,3,3,3-tetrafluoropropyl ether (C1BFE), were synthesized and their phase transition behaviours and electro-optical properties investigated by DSC, polarizing optical microscopy, Abbe refractometry and other physical methods. All the C2BFE compounds showed a layered mesophase like SmB, while C2BFE had no mesophase. All the fluorinated compounds have good solubility in ZLI-1132 (more than 15 wt %) and can be used as a component for lowering the refractive anisotropy (Delta n ) of the nematic solvent ZLI-1132.     

Liquid Crystalline Organisation and Reaction Rate in the Formation of Liquid Crystal Thermoset Networks from Diepoxides and Dicyanates

Summary: The influence of the type of mesophase on the rate of reaction in amine curing or anionic polymerisation of mesogenic diepoxides, and in the cyclotrimerisation of mesogenic dicyanates has been investigated by isothermal DSC and IR-spectroscopy. Epoxide/amine systems were found to react faster in the nematic than in the isotropic phase. Anionic polymerisation of epoxides is an example where increase of the reaction rate occurs with the transition from a mesophase of higher order (smectic) to phases with lower order (nematic, isotropic). For triaromatic dicyanates with one or three methyl groups at the central ring cyclotrimerisation is faster in the isotropic than in the nematic phase showing an increase of activation energy in the nematic phase with the number of methyl groups. A pronounced rate increase has been observed in the smectic phase as compared to the nematic phase for the unsubstituted triaromatic dicyanate. In this case activation energies in the two phases are comparable with those of non liquid crystalline dicyanates.     

Preparation and properties of laterally multifluorinated benzoxazole-based nematic mesogens

Series of laterally multifluorinated heterocyclic compounds, 2-(2?,3-difluoro-4?-alkoxy-1,1?-biphenyl-4-yl)-benzoxazole derivatives (nPF(2)PF(3)Bx), are prepared and characterised. They mainly display enantiotropic nematic mesophases with wider mesophase ranges of 12–107°C (heating process) and 22–134°C (cooling process) than the corresponding analogues. The enhanced nematic mesophase stability is achieved via slightly increasing inter-ring twist angle with inter-ring lateral fluorine substitute in biphenyl unit, as well as through improving the molecular polarity with multifluorine substitutes. Meanwhile, two inter-ring lateral fluorine atoms lead to a decrease in melting/clearing points and a wide nematic mesophase range, which makes it possible for heterocyclic mesogens nPF(2)PF(3)Bx to use in nematic liquid crystal display mixtures.     

Mesomorphic properties of achiral halogen-substituted banana-shaped compounds

Three banana-shaped achiral compounds, derivatives of 4,6-dichloro-1,3-phenylene bis-[4-(4- n -octyloxyphenyliminomethyl) benzoate], were synthesized by varying the substituent ( X =H, F and Cl). Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray analysis. The compound with X = H exhibited an enantiomeric nematic phase. The compounds with X = F and Cl formed a nematic phase on heating, while on cooling they formed a nematic phase at high temperature and a smectic A phase at a lower temperature (monotropic). A schematic representation of the mesophase structures for the compound with X = F is also illustrated.     

Nematic Triphenyltriazine Triesters and the Induction of the Columnar Mesophase by Fluorine Substitution

Whereas their para homologs are not mesogenic, the disk-shaped triphenyltriazine meta-trialkylesters obtained via trimerization of 3-cyanobenzoic alkylester, which are configurationally more flexible, exhibit a monotropic nematic mesophase. Introduction of fluorine atoms into the alkyl chains or into the phenyl moieties leads to the appearance of an enantiotropic columnar mesophase. If fluorine is introduced both in the chains and in the phenyl moieties, only a monotropic mesophase remains. Fluorination of either the alkyl chains or the aromatic core, but not both, appears thus as a simple means of inducing or stabilizing columnar self-assembly in disk-shaped systems. As the homeotropically alignable columnar mesophase can thus be made to persist at room temperature, as energies higher than 3 eV of the first excited triplet state are computed in agreement with the value reported for the parent arene, and as they are not fluorescent themselves, these compounds are of promise as aligning host matrices for blue-emitting TADF devices with improved light outcoupling. Dilution of a columnar with a nonmesogenic homolog induces the nematic state, indicating that the nanoscopic make-up of both mesophases is closely related.     

Transformation of a kinetically controlled nematic phase of a linear polymer into one which is thermodynamically controlled via cyclization [1]

The synthesis and characterization of cyclic main chain liquid-crystalline oligomers based on 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)butane (TPB) with 1,7-dibromoheptane (TPB-7(c)] are described. These oligomers were synthesized by the phase transfer catalysed polyetherification of TPB with 1,7-dibromoheptane under high dilution conditions and separated by column chromatography. Their cyclic structure was confirmed by 200 MHz ¹H NMR spectroscopy. The mesomorphic behaviour of TPB-7(c) was characterized by differential scanning calorimetry and polarized optical microscopy. The cyclic dimer is only crystalline, while the cyclic trimer, tetramer and pentamer exhibit an enantiotropic nematic mesophase. The high molecular weight linear homologue TPB-7(1) exhibits a nematic mesophase which has an isotropization transition temperature located in the very close proximity of its glass transition temperature. Therefore, this nematic phase is kinetically controlled. Due to the higher rigidity of cyclics versus linear structures the cyclic trimer, tetramer and pentamer exhibit higher isotropization transition temperatures than their linear homologue. Subsequently, the kinetically controlled nematic mesophase of the linear homologue is transformed into a thermodynamically controlled phase via cyclization.     

Dependence of Mesomorphic Behaviour of Methylene‐Linked Dimers and the Stability of the NTB/NX Phase upon Choice of Mesogenic Units and Terminal Chain Length

Twelve symmetrical dimeric materials consisting of a nonamethylene (C9) spacer and either phenyl 4‐(4′‐alkylphenyl)benzoate, phenyl 4‐(4′‐alkylcyclohexyl)benzoate or phenyl 4‐(4′‐alkylbicyclohexyl)carboxylate mesogenic units were prepared and their mesogenic behaviour characterised by POM, DSC and XRD. All of the materials exhibited nematic phases with clearing points in excess of 200 °C. Four compounds were found to exhibit the twist‐bend nematic phase, with one material exhibiting a transition from the N_TB phase into an anticlinic smectic ‘X’ phase. Across all three series of compounds the length of terminal chain is seen to dictate, to some degree, the type of mesophase formed: shorter terminal chains favour nematic and N_TB mesophases, whereas longer terminal aliphatic chains were found to promote smectic phases.     

Nematic mesophase enhanced via lateral monofluorine substitution on benzoxazole-liquid crystals

Fluorine is widely used as a lateral substituent to modify the physical properties of liquid crystals. Here, laterally monofluorinated compounds, 2-(4?-alkoxy-2-fluorobiphenyl-4-yl)-benzoxazole derivatives (nPPF(2)Bx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(2)BH, nPPF(2)BM and nPPF(2)BN, respectively) at 5-position, were synthesised and characterised. It is interesting to note that these only display enantiotropic nematic mesophases with mesophase ranges of 12–28°C and 13–45°C on heating and cooling for nPPF(2)BH, 46–97°C and 62–120°C for nPPF(2)BM and 82–108°C and 87–113°C for nPPF(2)BN, which are very different from the corresponding monofluorine-substituted analogue (compounds I) with enantiotropic smectic or smectic/nematic mesophases. The enhanced nematic mesophase is attributed to the reduced π–π interaction/conjugation resulting from the twisted structure of the molecule caused by the introduction of a fluorine atom into the inter-ring of the biphenyl unit. These results suggest that modification of the monofluorine substituent position is an effective method to improve the nematic mesophase in benzoxazole-liquid crystals.     

一种新型甲壳型液晶高分子的设计与合成

甲壳型液晶高分子是我国科学家最早设计和合成、受到国际学术界广泛关注的一类新型液晶高分子[1～ 6 ] .迄今已合成出 1 0个系列 1 0 0多种甲壳型液晶高分子 ,其中多数以乙烯基氢醌 [7] 、乙烯基对苯二胺 [8] 、乙烯基对苯二甲酸 [9] 和 2 -羟基 - 5-氨基苯乙烯 [10 ] 为关键中间体 .液晶核由 3个苯环以— COO—或— CONH—连接而成 .由于— COO—和— CONH—易与阳离子和阴离子相互作用 ,故已报道的甲壳型液晶高分子都是由自由基聚合反应制得 ,而很难用离子型聚合反应合成 .本文设计合成了一类未见文献报道的小分子液晶化合物 ,由此…     

Liquid crystal polymers containing macroheterocyclic ligands. III. Side chain liquid crystalline polymethacrylates containing mesogenic units based on diarylacetylenes and benzo-15-crown-5

The synthesis and polymerization of 4′-[4-ethynyl-1-(11-methacryloylundecan-1-yloxy) benzene] benzo-15-crown-5 ( 8 ), 4′-[4-ethynyl-4′-(11-methacryloylundecan-1-yloxy) biphenyl] benzo-15-crown-5 ( 15 ), 4′-[2-ethynyl-6-(11-methacryloylundecan-1-yloxy) naphthalene] benzo-15-crown-5 ( 24 ), and 4′-[2-ethynyl-6-(11-methacryloylundecan-1-yloxy)naphthalene]-5′-ethylbenzo-15-crown-5 ( 35 ) is described. The synthesis and characterization of 4′-[4-(4-ethynyl-1-(2-ethynyl-6-(6-hydroxyhexan-1-yloxy)naphthathalene)benzene]) benzo-15-crown-5 ( 29 ) is also presented. Both monomers and polymers were characterized for their mesomorphic behavior. 8 , poly( 8 ), and 15 are crystalline. Due to the insolubility of 15 , poly( 15 ) could not be synthesized. 24 is crystalline, while poly( 24 ) displays a monotropic nematic mesophase. 29 exhibits also a monotropic nematic mesophase. 35 is crystalline, while poly( 35 ) displays an enantiotropic nematic mesophase which is kinetically controlled due to its close proximity to the glass transition temperature.     

Synthesis and study the liquid crystalline properties of compounds containing benzoxazole core and terminal vinyl group

Terminal vinyl-based benzoxazole liquid crystalline compounds, 2-(3-fluoro-4?-alkoxy-1,1?-biphenyl ?4-yl)-5-(2-propenyloxymethyl)-benzoxazole (nPPF(2)BP), were synthesised and their structures were confirmed by infrared (IR) spectra, proton nuclear magnetic resonance (¹H-NMR) spectra, gas chromatography with electron impact-mass spectrometry (GC/EI-MS), matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and elemental analysis (EA). The compounds show enantiotropic smectic/nematic phases with mesophase ranges are 71–97 °C and 87–136°C on heating and cooling processes for nPPF(2)BP, respectively. They give low melting points due to lateral fluoro substituent and flexible terminal 2-propenyloxymethyl chain. It is found that the compounds nPPF(2)BP with shorter alkoxy chain (n = 3, 4) exhibit a wide range of nematic mesophase, which is ascribed to enhanced π–π interaction caused by terminal vinyl moiety, whereas further elongation of the terminal alkoxy chain results in supressing nematic phase and increasing smectic mesophase. Compared with methyl terminated analogues, 2-propenyloxymethyl terminated compounds nPPF(2)BP display much lower melting points and wider or comparable mesophase range both in heating and cooling.