Shear‐Induced Spiral‐Like Morphology of a Main‐Chain Liquid Crystalline Poly(aryl ether ketone)

The shear‐induced spiral‐like morphology of a main‐chain thermotropic liquid crystalline poly(aryl ether ketone) is observed and characterized by means of polarizing light microscopy, atomic force microscopy, transmission electron microscopy and electron diffraction techniques. The spiral‐like texture is formed during shearing in the temperature range of liquid crystalline to isotropic transition (335–340°C), and dispersed discontinuously in the mosaic matrix. Electron diffraction results indicate that the spiral exhibits orthorhombic lateral packing of the crystals and homeotropic alignment of the molecules. The spiral formation process and possible affecting factors are discussed.     

Electrodeposition of mesoporous semimetal and magnetic metal films from lyotropic liquid crystalline phases

Mesoporous semimetal bismuth film and magnetic metal nickel and cobalt thin films have been electrodeposited from hexagonal or lamellar structured lyotropic liquid crystalline phases with polyoxyethylene surfactant. The liquid crystalline templates are characterized by low-angle X-ray diffraction (XRD) and polarized-light optical microscopy (POM). The metal films are characterized by low-angle and wide-angle XRD, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The magnetic measurements on the mesoporous nickel and cobalt films are shown to have higher coercivity (Hc) than the nonporous polycrystalline films.     

Preparation of highly exfoliated epoxy/clay nanocomposites by clay grafted with liquid crystalline epoxy

Epoxy/clay nanocomposites with a high degree of exfoliation were achieved by intercalating liquid crystalline epoxy into clay intragallery as well as using a so-called ‘solution compounding’ process. In this process, clay modified was first treated with trichloromethane to form organoclay-trichloromethane suspension followed by liquid crystalline epoxy modification. The liquid crystalline epoxy grafted clay was then mixed extensively with epoxy to form epoxy/nanoclay composites. The mechanism of exfoliation was explored by monitoring the change of morphology of organoclay during each stage of processing with X-ray diffraction (XRD). The liquid crystalline epoxy grafted clay synthesised was characterised by fourier transform infrared spectroscopy (FT-IR) and polarising optical microscopy (POM). The clay platelets uniformly dispersed and highly exfoliated in the whole epoxy matrix were observed using transmission electron microscopy (TEM) and FT-IR imaging system. The epoxy nanocomposites were fabricated by incorporating different liquid crystalline epoxy grafted clay loading. The results revealed that the incorporation of liquid crystalline epoxy grafted clay resulted in a significant improvement in glass transition temperature (Tg) derived from dynamic mechanical analysis (DMA) and thermal stability measured by thermogravimetric analysis (TGA).     

Cryo-TEM studies of DNA and DNA–lipid structures

Studies published between 2001 and 2005 that utilise cryogenic transmission electron microscopy as a tool for investigating solutions containing DNA with or without amphiphiles present are reviewed. DNA or oligonucleotides form complexes with amphiphilic molecules such as lipids, so-called lipoplexes, and the structures and morphologies are excellent objects to study by cryogenic transmission electron microscopy. Recent studies show that this technique is an effective tool for identification of a range of structures such as unilamellar or multilamellar vesicles or dispersed liquid crystalline phases.     

Thermotropic and lyotropic liquid crystalline behaviour of 4-alkoxyphenyl beta-D-glucopyranosides

The liquid crystalline properties of a series of 4-alkoxyphenyl beta -D-glucopyranosides (methoxy to decyloxy and dodecyloxy) were studied using polarized light microscopy and differential scanning calorimetry. The compounds with the shortest alkoxy substituents are not liquid crystalline. The butoxy derivative displays a monotropic smectic A phase and the higher homologues display enantiotropic smectic A phases. The lyotropic behaviour was studied as a function of concentration and temperature. Hexagonal, cubic and lamellar phases were observed for compounds with alkoxy chains longer than butoxy. The nonyloxy derivative forms long ribbons in dilute solution as revealed by electron microscopy.     

Synthesis and characterization of liquid crystalline polysiloxanes containing benzyl ether mesogens

Side chain liquid crystalline polysiloxanes were synthesized by the hydrosilation of poly(methylhydrosiloxane) with p-(1-undecenyl-11-oxy) benzyl ethers of 4-cyanophenol (IM), 4-methoxyphenol (IIM), 4-cyano-4′-hydroxybiphenyl (IIIM), 4-methoxy-4′-hydroxybiphenyl (IVM), and 2-cyano-6-hydroxynaphthalene (VM). The phase behavior of both monomeric and polymeric liquid crystals was characterized by differential scanning calorimetry and optical polarization microscopy. IM is a monotropic liquid crystal, IIM is crystalline, and IIIM and IVM are enantiotropic liquid crystals, whereas VM presents two virtual liquid crystalline transitions and crystalline polymorphism. All the synthesized polysiloxanes present enantiotropic smectic mesomorphism.     

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3‐bis[4‐(4′‐aminophenoxyl) cumyl] benzene

The double melting behavior of a thermotropic liquid crystalline polyimide was studied by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). This liquid crystalline polyimide exhibited a normal melting peak around 278 °C and transformed into a smectic A phase. The smectic A phase changed to nematic phase upon heating to 298 °C, then became isotropic melt around 345 °C. The samples annealed or isothermally crystallized at lower temperature showed double melting endotherms during heating scan. The annealing‐induced melting endotherm was highly dependent on annealing conditions, whereas the normal melting endotherm was almost not influenced by annealing when the annealing temperature was low. Various possibilities for the lower melting endotherm are discussed. The equilibrium melting points of both melting peaks were extrapolated to be 283.2 °C. Combined analytical results showed that the double melting peaks were from the melting of the two types of crystallites generated from two crystallization processes: a slow and a fast one. Fast crystallization may start from the well‐aligned liquid crystal domains, whereas the slow one may be from the fringed or amorphous regions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3018–3031, 2000     

Compatibilization of PBT/PP Blends by Adding Side-chain Liquid Crystalline Ionomer with Quaternary Pyridinium Groups

A side-chain liquid crystalline ionomer(SLCI) was synthesized by grafting copolymerization of 4-(4-ethoxybenzoyloxy)-4′-allyloxybiphenyl and N-allyl-pyridium bromide on polymethylhydrosiloxane. The SLCI was blended with polypropylene(PP) and polybutylene terephthalate(PBT) by melt mixing. The thermal behavior, liquid crystalline properties, morphological structure, and mechanical properties of the blends were investigated by differential scanning calorimetry(DSC), polarizing optical microscopy(POM), scannin...     

Phase Transfer Catalysis in the Polycondensation Processes. XXV. The Relationship Between Structure and Supramolecular Ordering of Some Aromatic Polyethers Containing Flexible Spacer

Abstract

The paper presents a study concerning the influence of the chemical structure on the supramolecular ordering [crystalline, liquid crystalline (LC), or amorphous] of some aromatic polyethers. The polymers were synthesized using a phase transfer catalysis technique, in a liquid/liquid system, starting from 1,4‐dichlorobutane or 1,5‐dichloropentane and various bisphenols, as follows: 4,4′‐dihydroxyazobenzene (DHAB), 4,4′‐dihydroxydiphenyl (DHD), bisphenol A (BPA), and 2,7‐dihydroxynaphtyl (DN). All polymers were characterized by using ¹H‐NMR, DSC, and optical microscopy in polarized light. Some samples containing azobenzene moieties showed LC properties, but the majority of them resulted as semi‐crystalline compounds. If a bent bisphenol was used (BPA) to obtain homopolymers or copolymers, only amorphous products were obtained. The low thermal stability of the LC products generated some difficulties regarding the characterization of the mesophase. Generally, the copolymerization reaction influenced only the crystalline melting points, the isotropization temperature of the LC polymers being situated near their thermal degradation limit.     

Improvement of the properties of polyarylate reinforced with liquid crystalline polymers

Blends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.     

PDLC-like patterns at the isotropic to cholesteric transition entrapped by in situ photopolymerization

When investigated by optical microscopy between crossed polarizers, the isotropic to cholesteric transition may appear like fingerprint-patterned droplets embedded in a black isotropic matrix. In the present work, such PDLC-like (polymer dispersed liquid crystal) patterns, only occurring over 0.7 C, have been entrapped and stored at ambient temperature in a polymer film. We used a UV polymerization process with different sequences in which illumination time and UV power progressively vary. From a conceptual viewpoint, these PDLC-like patterns come solely from liquid crystalline material, whereas all the conventional PDLCs are binary mixtures of a macromolecular compound or 'prepolymer' with a conventional low molecular mass liquid crystal. The fact that isotropic matrix and cholesteric droplets differ only from the viewpoint of molecular order and not in their chemical nature, permits comparisons with the usual case for which the choice of polymer-forming material is crucial and the polymer/liquid crystal interface is an important factor for controlling PDLC electro-optic properties. The present system gives an opportunity to investigate by scanning electron microscopy (SEM) the droplet microstructure (isotropic-cholesteric interface, fingerprint patterns or defects), whereas previous SEM studies were focused on the shape and size of empty cavities, since the fluid liquid crystal was inevitably removed from the PDLC system.     

Cholesteric liquid crystals: Image contrast in the TEM

Bright-field image contrast of thermotropic cholesteric liquid crystalline materials in the transmission electron microscope (TEM) is investigated. Possible sources of contrast for these systems are discussed in terms of their molecular anisotropy. A cholesteric side-chain liquid crystalline compound was investigated with TEM, low voltage high resolution scanning electron microscopy (LVHRSEM), and atomic force microscopy (AFM) to determine the origin of the strong contrast observed in these systems using bright-field transmission electron microscopy. Initial contrast of thin microtomed sections, as viewed with TEM low dose techniques and an image intensifier, was much weaker than observed under normal viewing conditions. The periodic steady state contrast typically observed for these materials is the result of beam damage. Furthermore, the surface of microtomed samples (parallel to the cholesteric helical axis) is corrugated with a periodicity of 1/2 the pitch due to a preferred fracture path in the glassy cholesteric state. AFM profile analysis shows an average peak to valley height of approximately 20-25 nm. AFM of free surfaces from aligned films also indicates a corrugation with a periodicity equal to 1/2 the pitch with substantially smaller average corrugation depths. TEM indicates a series of +1/2 and -1/2 disclination lines at the surface due to a rotation of the preferred helix direction parallel to the surface, consistent with previously reported models.     

Interface induced crystal structures of dioctyl-terthiophene thin films

Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.     

STUDY ON THE BLENDS OF NYLON 66 AND LIQUID CRYSTALLINE POLYESTERS

Blends of polyamide (Nylon 66) with two different kinds of liquid crystalline polyesters were studied in all the composition range. Homogeneous samples were obtained by coprccipitation from 2 wt%. solution of blends. The thermal properties, crystallinity and morphology of these blends were studied by using DSC, polarizing microscopy, and scanning electron microscopy. The phase transition and morphology of the blends are markedly-influenced by the composition of liquid crystalline polyesters. The mechanical behaviour of PHB/HNA-Nylon 66 blend was improved. although polyamidc (Nylon 66)with the liquid crystalline polyesters were incompatible, but a rather strong interaction between the polymers did exist.     

Shear-induced phase transitions in sucrose ester surfactant

The behavior of a commercial sucrose stearate blend has been examined by means of various experimental techniques (differential scanning calorimetry, light polarization and electron microscopy, and rotational rheometry). A partial phase diagram in water has been established. It shows that the binary system forms a lamellar lyotropic mesophase and that the melting behavior is characterized by a lamellar gel-lamellar liquid crystalline phase transition. The identification of the liquid crystalline phase has been carried out from textural observation using polarization microscopy and freeze-fracture electron microscopy. At low surfactant concentrations, the phase transition has been followed through rheological experiments. Furthermore, a shear-induced transition, from the lamellar phase (sheets of surfactant bilayers including a few large multilamellar vesicles) to an onion phase, has been observed above a critical temperature of 43 degrees C. The vesicles so obtained did not relax over more than 3 weeks. The presence of a small ratio of distearate in the sugar ester blend seems to be the key to vesicle formation at low surface-active material concentration.     

Macromolecular cholesteric order observed by electron microscopy

The macromolecular cholesteric structure in the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA] cholesteric liquid crystalline solutions is studied by directly observing the morphology and structure of the ethyl-cyanoethyl cellulose [(E-CE)C]/polyacrylic acid [PAA] using electron microscopy. A periodical lamellar structure is observed in ultrathin slices of the composites with cholesteric order by both transmission electron microscopy (TEM) and low-voltage scanning electron microscopy (LVSEM). It is suggested that the periodical lamellar structure is induced by the twist of the molecular orientation in the cholesteric phase and reflects the structural features of the macromolecular cholesteric phase. The macromolecular cholesteric phase exhibits the twisted ring morphology in the initial stage of the formation of the liquid crystalline phase. The swelling of the ultrathin slices with cholesteric order in water is heterogeneous, which suggests the tight packing of the (E-CE)C chains in the direction of the helix axis in the macromolecular cholesteric phase. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 439–445, 1998     

一类含萘环结构的聚酯酰亚胺液晶聚合物的结构与性能研究

利用Higashi芳香聚酯直接缩聚法的原理,采用分步投料的方法,以N,N′-1,6-亚己基-双苯偏三酸酰亚胺二酸(IA6)、6-羟基-乙-萘甲酸(HNA)和4,4′-二羟基二苯酮(DHBP)为单体原料,合成了一系列聚酯酰亚胺共聚物.用核磁共振(NMR)、差热分析(DSC)、偏光显微镜(PLM)、广角X射线衍射(WAXD)、热重分析(TGA)等手段对所合成的聚酯酰亚胺的液晶行为、结构以及热性能进行了表征.研究结果表明,当HNA投料量占单体总投料量高于33mol%时,所得聚合物均呈明显的向列型热致液晶特性.但是,此类液晶聚合物仅在升温过程中出现液晶的相转变,而在降温过程中并未观察到液晶的相转变行为.由DSC结果分析可知,此类聚合物具有较高的玻璃化转变温度(Tg)和较低的熔融温度(Tm),有望成为一类既具有较低加工温度又有较高使用温度的液晶聚合物材料.     

Formation of ZnSe and CdS quantum dots via laser ablation in liquids

Formation of nanoparticles of both ZnSe and CdS under ablation of corresponding bulk semiconductors in liquid environment (diethyleneglycol, ethanol, etc.) using radiation of a Cu vapor laser is reported. X-ray diffraction (XRD), resonance Raman scattering (RRS), and transmission electron microscopy (TEM) confirm that the nanoparticles are crystalline and have average size of ca 10–20 nm. RRS of nanoparticles are characterized by several peaks multiple to frequency of corresponding phonon (LO replicas).     

Study of liquid crystal space groups using controlled tilting with cryogenic transmission electron microscopy

We developed a method that enables differentiation between liquid crystalline-phase particles corresponding to different space groups. It consists of controlled tilting of the specimen to observe different orientations of the same particle using cryogenic transmission electron microscopy. This leads to the visualization of lattice planes (or reflections) that are present for a given structure and absent for the other one(s) and that give information on liquid crystalline structures and their space groups. In particular, we show that we can unambiguously distinguish among particles having the inverted micellar cubic (space group Fd(3)m, 227), the inverted bicontinuous gyroid (space group Ia(3)d, 230), the inverted bicontinuous diamond (space group Pn(3)m, 224), and the inverted bicontinuous primitive cubic structure (space group Im(3)m, 229).     

Effects of alkyl chain length and anion size on thermal and structural properties for 1-alkyl-3-methylimidazolium hexafluorocomplex salts (C(x)MImAF6, x = 14, 16 and 18; A = P, As, Sb, Nb and Ta)

A series of 1-alkyl-3-methylimidazolium hexafluorocomplex salts (C(x)MImAF(6), x = 14, 16 and 18, A = P, As, Sb, Nb and Ta) have been characterized by thermal analysis, X-ray diffraction and polarized optical microscopy. A liquid crystalline mesophase is observed for all the C(16)MIm and C(18)MIm salts. The C(14)MIm(+) cation gives a liquid crystalline mesophase only with PF(6)(-). The temperature range of the liquid crystalline mesophase increases with an increase in alkyl chain length or with decrease in anion size. Single-crystal X-ray diffraction revealed that all the C(18)MImAF(6) salts (A = P, As, Sb, Nb and Ta) are isostructural with each other in the crystalline phase and have a layered structure. The interdigitated alkyl chain of the cation has a bent shape like a spoon near the imidazolium ring in the crystalline phase at -100 °C and is tilted with respect to the sheets of the imidazolium headgroups and anions. An increase of temperature increases the ratio of an all-trans conformation to the bent conformation in the crystalline phase. X-ray diffraction and polarized optical microscopy suggested that the liquid crystalline mesophase has a smectic A(2) structure. The interlayer distance increases with a decrease in the anion size since the smaller anion has a stronger coulombic interaction with the imidazolium headgroup, resulting in the decrease of the interdigitated part to give a larger layer spacing.