The driving force for homeotropic alignment of a triphenylene derivative in a hexagonal columnar mesophase on single substrates

An interesting discotic triphenylene derivative, 2,7-biscarbethoxy-3,6,10,11-tetrapentyloxytriphenylene, can be homeotropically aligned on a large scale as a film on single substrates, i.e. the film with one side on the substrate and the other side freestanding. The alignment is achieved in a controlled condition close to a thermodynamic equilibrium state in a liquid crystal phase when interactions at the substrate surface are limited. Phase changing properties of this material are also a key factor in the alignment processes. The aligned structures are observed with an optical microscope. Within a single domain a hexagonal lattice of a d-spacing 16.3 Å is confirmed by X-ray diffraction measurement.     

对称型苯并菲盘状液晶研究进展

盘状液晶是近年来研究的一种新型光电材料,其独特的光电性能显示了巨大的应用前景,本文主要从类型与合成方面介绍了近年来对称型苯并菲盘状液晶的研究进展.     

Pressure-jump X-ray studies of liquid crystal transitions in lipids

In this paper, we give an overview of our studies by static and time-resolved X-ray diffraction of inverse cubic phases and phase transitions in lipids. In [section sign] 1, we briefly discuss the lyotropic phase behaviour of lipids, focusing attention on non-lamellar structures, and their geometric/topological relationship to fusion processes in lipid membranes. Possible pathways for transitions between different cubic phases are also outlined. In [section sign] 2, we discuss the effects of hydrostatic pressure on lipid membranes and lipid phase transitions, and describe how the parameters required to predict the pressure dependence of lipid phase transition temperatures can be conveniently measured. We review some earlier results of inverse bicontinuous cubic phases from our laboratory, showing effects such as pressure-induced formation and swelling. In [section sign] 3, we describe the technique of pressure-jump synchrotron X-ray diffraction. We present results that have been obtained from the lipid system 1:2 dilauroylphosphatidylcholine/lauric acid for cubic-inverse hexagonal, cubic-cubic and lamellar-cubic transitions. The rate of transition was found to increase with the amplitude of the pressure-jump and with increasing temperature. Evidence for intermediate structures occurring transiently during the transitions was also obtained. In [section sign] 4, we describe an IDL-based 'AXcess' software package being developed in our laboratory to permit batch processing and analysis of the large X-ray datasets produced by pressure-jump synchrotron experiments. In [section sign] 5, we present some recent results on the fluid lamellar-Pn3m cubic phase transition of the single-chain lipid 1-monoelaidin, which we have studied both by pressure-jump and temperature-jump X-ray diffraction. Finally, in [section sign] 6, we give a few indicators of future directions of this research. We anticipate that the most useful technical advance will be the development of pressure-jump apparatus on the microsecond time-scale, which will involve the use of a stack of piezoelectric pressure actuators. The pressure-jump technique is not restricted to lipid phase transitions, but can be used to study a wide range of soft matter transitions, ranging from protein unfolding and DNA unwinding and transitions, to phase transitions in thermotropic liquid crystals, surfactants and block copolymers.     

盘状液晶的性能及应用

简要介绍了盘状液晶的基本概念、分子结构和相态,综述了盘状液晶的分子结构对相的影响、自组装性能、电导性能、光学性能、磁学和铁电性能方面的最新研究进展.盘状液晶柱状相拥有高的有序性和电荷传输速率,作为新型有机半导体材料具有广阔的应用前景.最后,系统概述了盘状液晶材料的应用,并指出了盘状液晶在应用方面存在的问题以及解决问题的方法和建议.     

Phase development in the hardening process of two calcium phosphate bone cements: an energy dispersive X-ray diffraction study

This work was aimed at the application of an energy dispersive X-ray diffraction technique to study the kinetics of phase development during the setting and hardening reactions in two calcium phosphate bone cements. The cements under study are based on either tricalcium phosphate or tetracalcium phosphate initial solid phase, and a magnesium carbonate-phosphoric acid liquid phase as the hardening liquid. The application of the energy dispersive X-ray diffraction method allowed to collect the diffraction patterns from the cement pastes in situ starting from 1 min of the setting and hardening process. The only crystallized phase in both cements was apatite-like phase, the primary crystallization process proceeds during a few seconds of the setting reaction. Both the compressive strength and the pH value changes during the hardening period can be attributed to the transformations occurring in the intergranular X-ray amorphous phase.     

X-ray diffraction and optical studies of Langmuir-Blodgett films formed from azobenzene derivatives

X-ray diffraction data were used to construct the electron density profiles of Langmuir-Blodgett films formed from two azobenzene derivatives, before and after annealing at moderate temperatures. The annealing process caused phase changes to occur that were apparent in the changes in optically observed textures and X-ray diffraction patterns. Consideration of these changes led us to conclude that, before annealing, the Langmuir-Blodgett films possessed smectic liquid crystal A phases and, after annealing, one compound had a tilted, layered crystal phase and the other a tilted liquid crystal phase.     

Synthesis and characterization of novel liquid crystalline polymers containing cholesteryl pendant groups

In order to investigate the chiral effect of cholesteryl pendant groups on the induction of the cholesteric phase, a new cholesteryl-containing liquid crystalline monomer was synthesized and copolymerized with an achiral comonomer in various molar ratios. The layer-like arrangement of the smectic mesophase with different monomeric compositions of copolymers was investigated using an X-ray diffraction analysis. The cholesteric liquid phase was induced by the chiral segments; the dependence of the reciprocal central reflection wavelength on the mole fraction of the chiral monomer for copolymers was investigated. This paper demonstrates the effect of chiral pendant groups on the induction of the cholesteric phase and layered molecular arrangement of side-chain liquid crystalline polymers.     

Thin films of liquid crystal fumarates and a related acrylate

Five fumarate esters and one acrylate ester have been synthesized and their properties examined. Four of them can be deposited as multilayers by evaporation in vacuo, and three of this group behave as thermotropic smectic liquid crystals. We have attempted to stabilize the homeotropic smectic phase by polymerizing the film using UV light. In two cases we have been successful and have produced films which are resistant to prolonged heating in THF. We infer that these materials are both polymerized and cross linked. They retain their regular layer structure after polymerization, a behaviour which we have demonstrated by X-ray diffraction. We have also attempted to form Langmuir-Blodgett multilayers with these compounds and in four cases have been successful.     

Reflective liquid crystal wavefront corrector used with tilt incidence

To allow angular separation of the beam reflected off a liquid crystal wavefront corrector from the incident beam, it is convenient to introduce a small incident angle. This avoids using a beam splitter and the associated energy losses. The effect of the tilt incidence on the liquid crystal wavefront corrector was investigated in this paper. For a parallel aligned liquid crystal wavefront corrector, a simplified model was established and used to analyze the change of the phase modulation under the tilt incidence. The simulated results showed that the effect of the tilt incidence on the phase modulation can be ignored when the angle of tilt incidence is less than 6 degrees. The phase modulation related to the incident angle was measured and the changing trend was similar to the calculated results. The effect of the tilt incidence on the diffraction efficiency of the liquid crystal wavefront corrector was also discussed. The simulated results indicated that the reduction of the diffraction efficiency is less than 1% for incidence angles under 3 degrees. Last, a closed loop correction experiment was done with an incident angle of 1 degrees. After correction, the averaged peak to valley (PV) and root mean square (RMS) of the wavefront were down to 0.15 lambda and 0.03 lambda, respectively, and a resolvable image was acquired.     

Enhanced activity of hierarchical zeolitic material with ZSM-5 structure for the tert-butylation of phenol

Nanocrytsalline phase of hierarchical zeolite structure with ZSM-5 was successfully synthesised via a facile and new method using NR latex as a polymer macrotemplate for the liquid phase alkylation of phenol with tert-butanol. X-ray diffraction pattern, FT-IR spectrum and TEM observations confirm the formation of pure and nanocrystalline zeolite ZSM-5 phase. Catalysis measurements show that the prepared zeolite ZSM-5 phase leads to high phenol conversion and 2,4-di-TBP selectivity which is mainly due to the presence of the hierarchical porosity within the zeolite ZSM-5 phase as confirmed by FESEM and pore size analyses.     

The effect of size and shape variation in discotic liquid crystals based on triphenylene cores

The triphenylene core provides a versatile platform from which discotic liquid crystals can be constructed. Synthetic advances permit the effect that substantial or subtle variation on structure has on mesophase formation. Through comparison of many derivatives, from our studies and others, it appears that the discotic core should be viewed as the triphenylene unit plus the attached polarizable substituents. Disruption of these extended cores discourages mesophase formation.     

盘状液晶材料及电导性能研究的最新进展

盘状液晶分子易于形成柱状相结构材料,从而具有较高的电导特性,是理想的电载流子传输材料,可用于制备光电器件。本文主要介绍苯并菲、酞菁、六苯并冠等盘状液晶材料的制备、电导性能的研究以及在器件应用研究中如纳米导线、有机太阳能电池的最新进展。     

Cationic liposome-DNA complexes: from liquid crystal science to gene delivery applications

At present, there is an unprecedented level of interest in the properties and structures of complexes consisting of DNA mixed with oppositely charged cationic liposomes (CLs). The interest arises because the complexes mimic natural viruses as chemical carriers of DNA into cells in worldwide human gene therapy clinical trials. However, since our understanding of the mechanisms of action of CL-DNA complexes interacting with cells remains poor, significant additional insights and discoveries will be required before the development of efficient chemical carriers suitable for long-term therapeutic applications. Recent studies describe synchrotron X-ray diffraction, which has revealed the liquid crystalline nature of CL-DNA complexes, and three-dimensional laser-scanning confocal microscopy, which reveals CL-DNA pathways and interactions with cells. The importance of the liquid crystalline structures in biological function is revealed in the application of these modern techniques in combination with functional transfection efficiency measurements, which shows that the mechanism of gene release from complexes in the cell cytoplasm is dependent on their precise liquid crystalline nature and the physical and chemical parameters (for example, the membrane charge density) of the complexes. In [section sign] 5, we describe some recent new results aimed at developing bionanotube vectors for gene delivery.     

A new metal-organic crystal: Potassium thiourea chloride

The growth and characterization of a new nonlinear metal-organic crystal, potassium thiourea chloride (PTC), is reported. The growth of single crystals of PTC was accomplished by the slow evaporation solution growth method. Single crystal X-ray diffraction analysis confirms the crystal structure. The FT-IR analysis confirms the presence of sulfur to potassium bonds in the complex. From the optical spectrum PTC has a good optical transmission in the entire visible region, which is an essential requirement for a nonlinear crystal.     

Optical beam deflection by phase-controllable dual-period grating employing liquid crystal

A dual-period grating is proposed that can change the period and the phase difference in the grating structure, allowing the switchable diffraction allocation of transmitted light. Liquid crystal is assumed to be a variable-refractive-index medium confined in the grating grooves. The distribution of the transmitted diffraction efficiencies is analysed using a rigorous diffraction analysis for dual-period gratings and this reveals that the efficiencies can be maximized among the zeroth-, first-, and second-order waves successively according to the refractive index change in the liquid crystal. The analytical model provides insight into the operation of the device and emphasizes its potential application as an optical beam deflector with large deflection angles.     

Molten salt route of single crystal barium titanate nanowires

Rather long barium titanate nanowires have been synthesised by molten salt method without any organic surfactants. The crystal structure of barium titanate nanowires is identified by X-ray diffraction to be the tetragonal structure phase, Raman spectroscopy and selected area electron diffraction measurements. Furthermore, scanning electron microscopy and transmission electron microscopy observations show that the barium titanate nanowires have uniform cylindrical structure, with lengths from 20 to 80 μm and diameters from 100 nm to 1 μm. Moreover, high resolution transmission electron microscopy observations and selected area electron diffraction analysis show that the barium titanate nanowires are single crystals with a tetragonal structure in nature.     

Note on the crystal structure of V3O5

The observation of a great many very weak extra reflexions in the X-ray diffraction spectrum of a single-crystal of V₃O₅ indicates slight deviations from the centric atomic arrangement. The indicated space groups are P2/c and Pc with a unit cell orientation different from the one originally used. A recently reported phase transition near 150°C has been confirmed by DTA measurements.     

Holographic polymer dispersed liquid crystal enhanced by introducing urethane trimethacrylate

This work characterizes holographic polymer dispersed liquid crystals (HPDLC) composite material based on a new monomer, urethane trimethacrylate, by fabricating switchable diffraction grating. The highest diffraction efficiency achieved was 90.3%. Details of the fabrication and preliminary results of electro-optical switching of the HPDLC diffraction gratings are presented and discussed based on the functionality of the monomer. These experimental results are explained by means of morphological scanning electron microscopy analyses.     

Growth and characterization of a new metal-organic crystal: Potassium thiourea iodide

Single crystals of potassium thiourea iodide (PTI), a semiorganic nonlinear optical crystal, have been grown from low temperature solution growth method by a slow evaporation technique at room temperature. Single crystal X-ray diffraction pattern and FTIR spectrum analysis has confirmed the formation of the new crystal. PTI has good optical transmission in the entire visible region, which is an essential requirement for a nonlinear crystal.