有机光导液晶光阀(透射式)及其性能的研究

本文报道用聚乙烯咔唑-2,4,7三硝基芴酮电荷转移复合物作光导层,与向列型及胆甾向列型混合液晶组成的夹心池结构制成的扭曲场效应、相变存储效应及动态存储效应三种直流透射式光阀及其性能的研究结果。制得的光阀均有明显开关效应。此外,还详细研究了扭曲场效应液晶光阀的阈值电压、对比度及上升时间与写入光功率的依赖关系。用白光写入,He-Ne激光读出,在扭曲场效应光阀上可实现非相干光-相干光转换,得到图象。用MTF法测得的光阀分辨率为34lps/mm。     

Electro‐optic effects and phase behavior of liquid‐crystalline physical gels: self‐assembly of hydrogen‐bonded molecules for the formation of dynamically functional composites

Anisotropic physical gels of liquid crystals are obtained by the formation of non‐covalently‐bonded networks through self‐organization of low molecular weight compounds in nematic solvents. They exhibit thermoreversible transitions between isotropic liquid and isotropic gel, and between isotropic gel and liquid‐crystalline gel, whose temperatures are dependent on the components. Electro‐optic properties of liquid‐crystalline gels are examined with twisted nematic cells. A nematic liquid crystal in a gel structure can respond to electric fields twice faster than a single liquid‐crystalline component.     

Helical twisting power and compatibility in twisted nematic phase of new chiral liquid crystalline dopants with various liquid crystalline matrices

ABSTRACT

Four chiral dopants exhibiting smectic LC phases themselves were prepared and their helical twisting power (HTP) and thermal phase behaviour in mixtures with four various LC hosts were studied. The influence of host liquid crystal on HTP was evaluated and generally higher values were found for hosts with high birefringence. Unexpectedly, high enhancement was found for an LC-chiral dopant pair, both having a similar aromatic core – biphenyl ring substituted with polar group. All studied chiral dopants exhibited limited compatibility with the LC hosts in twisted nematic phase at room temperature. For one of the studied mixtures, it was able to obtain single twisted nematic phase with selective light reflection band with maximum at wavelength about 1.0 µm. Carboxylic acid-type dopants exhibited total compatibility with the studied host in single twisted nematic phase at elevated temperatures, allowing preparation of mixtures with reflection band in the visible range. In case of the carboxylic acid dopants, blue phases for optimised compositions were observed. Intermolecular hydrogen bonding between carboxylic acid proton and pyridine nitrogen of chiral dopants was found. Doping the LC host with these dopants led to slight enhancement of HTP value and higher solubility in the LC host.     

Modular assembly of elliptical mesogens

Discotic mesogens featuring a pyridine ring were synthesized, and were found either to form ordered hexagonal columnar liquid crystalline phases or melt directly from a crystal to an isotropic liquid, depending on the position of the pyridyl nitrogen atom. Binary mixtures of the mesogenic pyridine derivatives with a similar discotic mesogen having a carboxylic acid group resulted in the formation of modular elliptical complexes through hydrogen bonding. The binary mixtures were found to exhibit ordered hexagonal columnar or ordered rectangular columnar and nematic mesophases, depending on the length of the alkyl chains, and displayed dramatically different properties from their constituent components. Binary mixtures of the non-mesogenic pyridine derivatives with carboxylic acid-functionalized discotic mesogens did not result in the formation of hydrogen-bonded complexes.     

液晶显示材料

介绍了液晶的结构类型,液晶分子的光电效应,实现液晶显示的偏振片透光原理,包括扭曲向列型（TN）、超扭曲向列型（STN）、薄膜晶体管型（TFT）液晶显示的异同,可用于液晶显示的有机材料,以及液晶显示材料的产业现状及发展趋势。     

Polymer dispersed liquid crystal display device for projection high definition television application

Polymer dispersed liquid crystal (PDLC) is a light scattering material that operates on the principle of electrically modulating the refractive index of the liquid crystal in an optical isotropic, transparent solid. The principle of operation of the PDLC device, the interface requirements between PDLC material and its driving circuit are studied. For high definition television (HDTV) application, a detailed comparison of PDLC vs. twisted nematic/super twisted nematic (TN/STN) display devices will be discussed. It was found that single crystal metal oxide semiconductor field effect transistor (MOSFET) is better than conventionally used thin film transistor (TFT) in driving these PDLC light valves.     

Dynamic response of super-twisted nematic liquid crystal displays

The dynamics of super-twisted nematic (STN) liquid crystal displays was studied by detailed computer simulation. The time evolution of director configuration and velocity of flow as obtained by solving Ericksen-Leslie hydrodynamic equations. The influence of d/p value and pretilt angle on the dynamic response was also studied. A comparison was also made between twisted nematic and STN liquid crystal displays.     

Self-assembled discotic nematic liquid crystals formed by simple hydrogen bonding between phenol and pyridine moieties

New discotic nematic liquid crystals have been prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) and the peripheral molecules of stilbazole derivatives. The various nematic phases formed by new hydrogen bonding building blocks were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The first discotic complexes of PG and trans-4-alkoxy-4′-stilbazoles exhibited nematic columnar (N_C) and hexagonal columnar phases depending on the length of alkyl chains, which were considered as the basic discotic structure. Several structural variations on the building blocks were attempted to examine their effects on the liquid crystalline properties of discotic complexes. The nematic lateral phase (N_L) with enhanced intercolumnar order was observed for the complexes of PG and trans-4-cyanoalkoxy-4′ stilbazoles due probably to the strong dipole interactions between cyano groups at the end of alkoxy chains. By introducing the nonlinear structure in three arms of supramolecular discotic mesogen, a discotic nematic phase (N_D) was observed for the complex of THPB and trans-4-octyloxy-4 -stilbazole. The single hydrogen bonding between phenol and pyridine moieties in this study provides a simple and effective method for preparing the rarely found discotic nematic liquid crystals.     

Dynamic response of super-twisted nematic liquid crystal displays

The dynamics of super-twisted nematic (STN) liquid crystal displays was studied by detailed computer simulation. The time evolution of director configuration and velocity of flow as obtained by solving Ericksen-Leslie hydrodynamic equations. The influence of d/p value and pretilt angle on the dynamic response was also studied. A comparison was also made between twisted nematic and STN liquid crystal displays.     

Liquid crystalline oxygen containing heterocyclic derivatives

This paper presents a review of the work on the molecular design of oxygen containing heterocyclic liquid crystals for nematic liquid crystal display applications and examines in some detail the correlations between the molecular structure of liquid crystalline oxygen containing heterocyclic derivatives and their physico-chemical and electro-optical properties.     

Anchoring effects on the electrically controlled optical band gap in twisted photonic liquid crystals

We study a one-dimensional twisted photonic liquid crystal (TPLC), consisting of various nematic liquid crystal cells adopting a twisted configuration intercalated by isotropic dielectric layers, submitted to a dc electric field (E^dc ) aligned along the periodicity axis. We write the corresponding Euler–Lagrange equations describing the nematic layer configuration. By assuming arbitrary anchoring quasi-planar boundary conditions, we calculate the equilibrium textures for the nematic, parametrized by the two types of strength of its interaction (polar and azimuthal) with the plane walls. We write the electromagnetic equations in a 4?×?4 matrix representation and using the transfer matrix formalism, we obtain the transmittance and reflectance coefficients for normal incidence as functions of the external electric field and anchoring strengths. We have observed a remarkable dependence of the electric field on the transmission and reflection spectra in opening and closing band gaps.     

Memory effects in chiral nematic liquid crystals doped with functionalised single-walled carbon nanotubes

Octadecylamine-functionalised single-walled carbon nanotubes (SWCNTs) were dispersed into nematic liquid crystals (LCs) doped with chiral molecules. The collective orientation of nematic LC molecules in helical layers was manipulated by varying dopant concentration. Highly anisotropic nature of SWCNTs enhanced the anisotropy of the LC as confirmed by polarised fluorescence spectroscopy. The π–π interaction of SWCNTs present in the planar alignment layers and twisted nematic LC molecules affects the molecular relaxation process. An irreversible electro-optic memory in the material has been observed.     

Amorphous twisted nematic liquid crystal displays: The characteristics and the theoretical considerations

Amorphous twisted nematic liquid crystal display cells have been prepared without rubbing. The textures consisted of twisted nematic multi-domains. Theoretical calculations of the optical properties of such cells have been carried out by the 4 × 4 matrix method. The optical anisotropy of the liquid crystal is optimized to suppress/optimize the background colour. The electro-optical characteristics of the a-TN have been measured. It is shown that the a-TN devices exhibit wide and uniform viewing angle characteristics and possess good gray scale capability. Viewing angles of - 47° to + 45° (up-down) and - 51° to + 46° (left-right) have been achieved. A rise time of 36.5 ms and decay time of 35.5 ms have been measured in an a-TN sample.     

Elastic model for twisted nematic textures in OOBA layers

An elastic model for the twisted nematic texture observed in nematic cells containing octyloxybenzoic acid is proposed. According to the model the twisted textures are due to the presence of cybotactic groups which are responsible for the chirality of the liquid crystal. We show that by assuming for the density of cybotactic groups a critical temperature behaviour close to a special temperature, the experimental data can be well interpreted by our mechanical model.     

Supramolecular hydrogen-bonded liquid–crystalline polymer complexes. Design of side-chain polymers and a host–guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.     

Analysis of operation mode of reflective twisted nematic liquid crystal display devices with rear film compensation

The rear film compensated reflective twisted nematic liquid crystal display device was studied in normally black and normally white operation conditions using a dynamic parameter space method. The electro-optical responses and reflectance spectra were also studied for different operation modes. A comparison was made between rear film and front film compensated reflective twisted nematic liquid crystal displays. We show that high quality normally white or normally black modes can be obtained by placing the fast axis of a quarter wave plate at 45° or 0° to the input director direction. The viewing angle characteristics of the optimum modes were also studied.     

Analysis of operation mode of reflective twisted nematic liquid crystal display devices with rear film compensation

The rear film compensated reflective twisted nematic liquid crystal display device was studied in normally black and normally white operation conditions using a dynamic parameter space method. The electro-optical responses and reflectance spectra were also studied for different operation modes. A comparison was made between rear film and front film compensated reflective twisted nematic liquid crystal displays. We show that high quality normally white or normally black modes can be obtained by placing the fast axis of a quarter wave plate at 45° or 0° to the input director direction. The viewing angle characteristics of the optimum modes were also studied.     

Field Effects in Nematic Liquid Crystals in Terms of Catastrophe Theory

The field effects in nematic liquid crystal layers are reanalysed using catastrophe theory. The layer with pretilted director orientation and obliquely applied magnetic field, the hybrid aligned nematic cell and twisted nematic structures are considered. The stable solutions are identified and transitions between them are specified. The results are in essential agreement with previous work. Some details concerning the behaviour near the threshold are revealed.     

A detailed derivation of extended Jones matrix representation for twisted nematic liquid crystal displays

A detailed derivation of the extended Jones matrix representation for twisted nematic liquid crystal displays at oblique incidence (which was previously published by the author) is given. It is shown that this representation reduces to the well-known ordinary Jones matrix representation at normal incidence.     

Twist molecular orientation transition in a nematic liquid crystal cell

We theoretically demonstrate that the application of a transverse next-to-static electric field to a planar nematic liquid crystal cell - obtained by strong planar anchoring of the liquid crystal on the first surface and negligible interaction with the second surface - causes an electro-reorientational transition of the Freedericksz kind. We show that, above the transition the cell behaves as a twisted nematic liquid crystal cell with total twist depending on the applied voltage. Preliminary experimental results confirming the predicted effect are presented.