Types Of Liquid Crystals Research Articles

Reducing driving voltage and securing electro-optic reliability of in-plane switching liquid crystal display by applying polysulfone photoalignment layer with photo-reactive mesogens

Newly synthesised photocurable polysulfone (PSCMh) was applied as a photoalignment layer of in-plane switching liquid crystal display (IPS LCD). When the linear polarised ultraviolet light (LPUVL) was irradiated on the typical calamitic nematic liquid crystals on the PSCMh alignment layer, the liquid-crystal director was aligned perpendicular to the LPUVL. Based on the experimental results, it was realised that IPS LCD photoaligned by PSCMh with additional polymer layer associated with reactive mesogen (RM) showed a low driving voltage with reduction of 0.2 V compared to the rubbed cell and also excellent electro-optic reliability such as alignment stability, residual direct current and voltage holding ratio compared to the purely photoaligned cell. Therefore, it was concluded that the polymer stabilisation of PSCMh with RM was effective for improving IPS LCD performances.

액정을 이용한 반사형 가변 광 감쇠기

본 논문은 광스위치등에 사용되는 가변 광감쇠기를 위해 반사형 액정셀을 채용한 광감쇠기 구조를 제안하고 특성을 검토한다. 본 제안의 가변 광감쇠기는 반사형구조로 소형화가 가능하고 저전압구동이 가능하다. 광통신용 파장에 적합한 액정셀의 설계방법, 주변온도에 따른 동작특성, 광감쇠기의 응답특성 등을 검토하여 본 제안 구조의 유용성을 검증한다. This work studies a variable optical attenuator using a reflective type liquid crystal cell for optical switches. The proposed architecture is capable of comprising a compact and low voltage driving variable optical attenuator. The usefulness of the proposed architecture is demonstrated by showing characterization of the liquid crystal cell, temperature effects, and response characteristics of the architecture.

Fundamental emission characteristics of light-emitting liquid crystal cells with rubrene-doped 4-cyano-4’-pentylbiphenyl

We have investigated the light emission properties in rubrene-doped nematic liquid crystal (LC) cells from the following three standpoints: (i) effect of the heating temperature during the sample preparation, (ii) role of the emissive LC layer thickness, and (iii) role of different LC types used as the emissive layer. As a result, the light-emitting LC cells simultaneously exhibit the features of electrochemiluminescent cells (the carrier transport is governed by an ionic conduction) as well as of organic light-emitting diodes (the luminance strongly depends on the emissive layer thickness). Furthermore, we report that devices with cyano group containing LCs exhibit higher luminance compared to a fluorinated LC.

Improved High-Frequency Performance of Microstrip-Line-Type Liquid Crystal Phase Shifter

A novel microstrip-line (MSL)-type liquid crystal (LC) phase shifter is designed to retain both the ease of fabrication with a coplanar waveguide (CPW)-type LC phase shifter and the excellent phase-shifting properties of the MSL-type one. The converting circuit, which is a key component of the device, is optimized so as to improve the operating frequency. Then, the phase-shifting properties and loss phenomena are investigated by using various LC materials. The operational frequency is extremely improved by employing a novel large birefringence LC material and the optimized design.

Adjustable Bistability and Hysteresis Loop in a Nd:GdVO4 Laser with an Intracavity Liquid Crystal Cell

Adjustable optical bistability and spatial hysteresis appearing in a Nd:GdVO4 laser with an intracavity liquid crystal (LC) cell were achieved. On the basis of optically induced LC reorientations and the varying magnitude of the order parameter, two types of LC were used to easily control the characteristics of hysteresis with a single control variable. Using an electrically driven twisted-nematic LC, an adjustable hysteresis area as well as a switching-on pump power was demonstrated and periodic spatiotemporal patterns were observed. By contrast, amplified hysteresis loops were obtained by increasing the rotation angle of homogeneous LC cells with a nearly invariable switching-on pump power.

Orientational Fluctuations Near the Smectic A to Smectic C Phase Transition in Two “de Vries”‐Type Liquid Crystals

On the basis of thorough analysis of 2D X-ray diffraction patterns from smectic monodomains, we examine the influence of orientational fluctuations on the weakly first-order smectic A (SmA) to smectic C (SmC) transitions in two nonchiral organosiloxane "de Vries"-type liquid crystals. We find that these materials exhibit very large molecular tilt fluctuations with magnitudes of up to 35°--thus larger than the average tilt itself. This is essential to understand the underlying molecular mechanism behind the practical absence of smectic layer contraction in these materials: in the SmA phase, the nematic order parameter is very low (molecular fluctuations correspondingly high), and the expected layer shrinkage at the SmA to SmC transition is almost fully compensated by the increase in orientational order, as the fluctuations diminish with decreasing temperature. In addition to the general tilt fluctuations, we observe intrinsic soft-mode fluctuations. They have a λ-shaped temperature dependence that peaks at the SmA-SmC transition with a maximum amplitude of about 2°.

Predicting the Anchoring of Liquid Crystals at a Solid Surface: 5-Cyanobiphenyl on Cristobalite and Glassy Silica Surfaces of Increasing Roughness

We employ atomistic molecular dynamics simulations to predict the alignment and anchoring strength of a typical nematic liquid crystal, 4-n-pentyl-4'-cyano biphenyl (5CB), on different forms of silica. In particular, we study a thin (~20 nm) film of 5CB supported on surfaces of crystalline (cristobalite) and amorphous silica of different roughness. We find that the orientational order at the surface and the anchoring strength depend on the morphology of the silica surface and its roughness. Cristobalite yields a uniform planar orientation and increases the order at the surface with respect to the bulk whereas amorphous glass has a disordering effect. Despite the low order at the amorphous surfaces, a planar orientation is established with a persistence length into the film higher than the one obtained for cristobalite.

Electro-optic characteristics of the fringe in-plane switching liquid crystal device for a liquid crystal with negative dielectric anisotropy

Fringe-field switching (FFS) liquid crystal (LC) mode is mainly used for high-end LC displays. At present, an LC with positive dielectric anisotropy is utilised, although light efficiency of the device in a white state is not maximised due to generation of tilt angle near the edge of electrodes along the field direction. In order to overcome the demerit, an LC with negative dielectric anisotropy has been challenged. In this article, FFS mode, which shows a high light efficiency and a low operating voltage, is investigated with the utilisation of fringe in-plane electric field. The optimised device shows improved electro-optic characteristics in comparison with not only conventional LC modes, but also previously proposed FFS device using a positive type of LC.

Preparation of Phenylenevinylene Derivatives Having Fluorescence and Chiral Induction Function

A series of chiral rod-like compounds with fluorescence was synthesized. The chemical structures of the materials thus synthesized were confirmed with 1H nuclear magnetic resonance spectroscopy (NMR), 13C NMR, and two-dimensional heteronuclear multiple quantum correlation (HMQC) methods. Furthermore, guest-host type liquid crystal (LC) devices were prepared using these compounds and electric field driven optical rotation switching of the LC devices based on change in helix-uniaxial orientation was demonstrated. The large optical rotation is derived from the helical structure of the ordered cholesteric LC. (Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.)

Steady-states for shear flows of a liquid-crystal model: Multiplicity, stability, and hysteresis

In this work, we study shear flows of a fluid layer between two solid blocks via a liquid-crystal type model proposed in [C.H.A. Cheng, L.H. Kellogg, S. Shkoller, D.L. Turcotte, A liquid-crystal model for friction, Proc. Natl. Acad. Sci. USA 21 (2007) 1–5] for an understanding of frictions. A characterization on the existence and multiplicity of steady-states is provided. Stability issue of the steady-states is examined mainly focusing on bifurcations of zero eigenvalues. The stability result suggests that this simple model exhibits hysteresis, and it is supported by a numerical simulation.

편광 흡수성 광기전성 고분자 박막 연구

We present the results of a study of the polarizing photovoltaic (PV) effects in an aligned polymer bulk heterojuction PV layer. The fairly uniform in-plane uniaxial alignment of the PV layer with a macroscopic axial orientational order parameter of 0.40 was achieved by means of a simple rubbing technique. Moreover, reflective polarizing PSCs having the aligned PV layers were applied to power-generating reflective type liquid crystal displays (LCDs), which exhibited a maximum contrast ratio of 1.7. These results form a promising foundation for various energy harvesting polarization dependent opto-electrical LCD device applications.

Orientational order parameters of a de Vries–type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction

The orientational order parameters (P{2}) and (P{4}) of the ferroelectric, de Vries-type liquid crystal 9HL have been determined in the SmA and SmC phases by means of polarized Raman spectroscopy, and in the SmA phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a "sugar loaf" orientational distribution in the SmA phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries-type behavior is considered.

Optical multi-stability of bimesogenic cholesteric liquid crystal

In this paper, we present a multi-stable property in a bimesogenic cholesteric liquid crystal material with a proper chiral additive and check its potential as an energy saving transmissive type liquid crystal display (LCD) through its electro-optic characteristics. Experimental results show that the multi-stable characteristics in the fabricated cholesteric LC cell are very stable. Such multi-stable properties depend on the driving frequency, voltage, and field direction. The contrast ratio in the fabricated transmissive type cholesteric LC cell was 15:1, which is a result produced by voltage and frequency control.

Small and Large Angle Quasi-Elastic Scattering Experiments by Using Nuclear Resonant Scattering on Typical and Amphiphilic Liquid Crystals

The microscopic slow dynamics with a time scale of around 100 ns in soft matters is important for understanding the origins of their mesoscopic structures. However, it is difficult to observe the slow dynamics at the microscopic level. Here, a newly developed time-domain interferometry (TDI) method using nuclear resonant scattering was applied to study the microscopic dynamics in a typical liquid crystal 4-cyano-4'-octylbiphenyl (8CB) and a partly fluorinated amphiphilic liquid crystal 11-(4'-cyanobiphenyl-4-yloxy)undecyl pentadecafluorooctanoate (BI) under a smectic A phase. As a result, the relaxation times of the molecular correlations in the intersmectic and intrasmectic layers could be obtained simultaneously by the TDI method and similar degrees of the anisotropic dynamical behaviour of 8CB and BI were observed.

The electro-optical characteristics of liquid crystal device in multi-component liquid crystal mixture system with non-contact photo-induced vertical alignment mode

In previous studies, we mixed photo-curable acrylic pre-polymer into negative dielectric anisotropy nematic type liquid crystal (N-type LC, NLC) to obtain a NLC/photo-curable acrylic pre-polymer mixture solution (NLC mixture system). After irradiation with UV light of fixed intensity, we successfully fabricated copolymer films with vertical alignment effect among the LC molecules. In this study, we propose a new type of multi-component LC mixture system by mixing chiral smectic type (SmA*) LC with homeotropic texture into NLC/photo-curable acrylic pre-polymer mixture system (NSLC mixture system). Our experimental results revealed that this SmA* LC exhibited the vertical alignment effect associated with LC molecules in the auxiliary LC mixture system. Moreover, we also discovered that altering the main chain type biphenol acrylic pre-polymer had drastic impact on the contrast ratio (CR) of the LC mixture system, with an increase of as much as 73%. More importantly, adding the SmA* LC can evidently increase the anchoring energy of the alignment film surface. We also further performed measurements, analyses, and discussions of electro-optical properties of devices fabricated from the new LC mixture systems.

笔段式LCD驱动设计

This paper mainly introduces the segment type liquid crystal display principle and control methods in design and application of digital display instrument.The liquid crystal display system made by Texas Instruments with ultra low power microcontroller CC430F6137,which has a segment type LCD controller,can drive 96 segments at most.The GD46532 LCD module is designed by DaLian JiaXian electronic Co.,Ltd.The authors design the driving program in temperature sampling system,and also give the twinkle display way to display the value of sampled temperature.By application testing,the digital instrument with LCD controller can reduce the system size to the largest extent.The system is high reliable.Its program is easily portable in other systems.

聚合物分散液晶的电场诱导定向聚合实验研究

The field induced stereo regular polymerization of polymer dispersed nematic liquid crystal both positive and negative dielectric character are experimentally studied,the picture in kind and polarizing microscope photograph of samples are given.The experiment results show that there are obvious distinguish with in different area of electric field applied or not,the electric field has the induced stereo regular polymerization action under the polymer dispersed liquid crystal sample preparation process.The experiment results are useful to understand the influence of polymer border condition to liquid crystal micro drop configuration,and are in a sense of gaining a good deal to design a new type liquid crystal display device.

Deep-Blue Photoluminescent Properties of a Liquid Crystal TB10A

A typical liquid crystal (LC) N,N-(terephthalylidene) bis (4-decylbenzenamine) (TB10A) was firstly synthesized at room temperature. The synthesized LC TB10A were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), ultraviolet-visible (UV-vis) spectrophotometry, photoluminecence (PL) spectroscopy and electronic structure calculations. Upon the 325 nm excitation, the dilute tetrahydrofuran solutions of TB10A could give off blue PL. With Hückel tight-binding method, the electronic structures of the TB10A were calculated. Our results demonstrated that the deep-blue PL observed at about 489 nm (2.54 eV) can be assigned to theπ* →ntransition for the TB10A.

Effect of Micro-Structural Light Guide Plate on Source of Linearly Polarized Light

In this work, three micro-structural plates are designed to guide linearly polarized light that is assumed to be emitted from four light emitting diodes in a typical compact liquid crystal display device. The brightness and uniformity of the emission from each guide plate are simulated for various orientations of linear polarized light. The experimental results show that the new light guide plate with two differently micro-structural v-cut surfaces provides higher brightness and uniformity of the output light.

Synthesis and Property of Liquid Crystal Polymers Containing Photosensitive Groups

The synthesis and free-radical polymerization of the acrylates monomer containing photosensitive chalcone group and the acrylates monomer containing mesogenic group are described in this paper. The monomers and polymers were characterized by FT-IR and 1 H NMR spectra. The thermal properties of polymers were measured by DSC and the liquid crystalline texture was measured by POM. And the results indicated that the polymers showed typical nematic phase and liquid crystal temperature range was 74 °C-103 °C.