Negative Liquid Crystal Research Articles

The influence of vicinal threo-difluorination on electro-optic and mesogenic properties of propyleneoxy-linked nematic liquid crystals

A protocol for the preparation of a series of liquid crystals is presented, where the structures carry a central propyleneoxy motif carrying two vicinal threo-C–F bonds. The negative dielectric anisotropy (−Δɛ) of the resultant liquid crystals has been explored. The stereoelectronic relationship between the vicinal C–F bonds was anticipated to orientate the fluorine atoms gauche to each other when the propylene chain is extended. This is shown to be the case. This orientation of the C–F bonds generates a net dipole perpendicular to the molecular axis, a prerequisite for the design of dielectrically negative liquid crystals. However the molecules adopt a conformation where one C–F bond reinforces the net molecular dipole, and the other has a counter effect, thus the introduction of the motif has an almost neutral effect on dielectric anisotropy (Δɛvirt) of these candidate liquid crystals. However, introduction of the difluoro motif raises the melting points of the liquid crystals and increases their conformational rigidity.

Fast switching of vertically aligned negative liquid crystals by optically hidden relaxation

We propose a method for fast switching of vertically aligned (VA) negative liquid crystals (LCs) by hiding the relaxation process of LCs. During the turn-off process, a strong in-plane electric field is applied for a short duration of time instead of relying solely on the slow relaxation of LCs. The LC molecules are rotated to the transmission axis of one of the polarisers by the applied in-plane electric field, resulting in turn-off switching that is 5.8 times faster than that of a conventional VA cell. By applying an overdriving scheme, we experimentally obtained a total response time of 3.3 ms.

Studies of nanocomposites of carbon nanotubes and a negative dielectric anisotropy liquid crystal

It has been widely recognized that the combination of carbon nanotube (CNT) and liquid crystals (LCs) not only provides a useful way to align CNTs, but also dramatically enhances the order in the LC phases, which is especially useful in liquid crystal display (LCD) technology. As the measure of this phase behavior, the complex specific heat is presented over a wide temperature range for a negative dielectric anisotropy alkoxyphenylbenzoate liquid crystal (9OO4) and CNT composites as a function of CNT concentration. The calorimetric scans were performed under near-equilibrium conditions between 25 and 95 °C, first cooling and then followed by heating for CNT weight percent ranging from ϕ(w) = 0 to 0.2. All 9OO4/CNT mesophases have transition temperatures ~1 K higher and a crystallization temperature 4 K higher than that of the pure 9OO4. The crystal phase superheats until a strongly first-order specific heat feature is observed, 0.5 K higher than in the pure 9OO4. The transition enthalpy for the nanocomposite mesophases is 10% lower than that observed in the pure 9OO4. The strongly first-order crystallization and melting transition enthalpies are essentially constant over this range of ϕ(w). Complementary electroclinic measurement on a 0.05 wt. % sample, cooling towards the smectic-C phase from the smectic-A, indicates that the SmA-SmC transition remains mean-field-like in the presence of the CNTs. Given the homogeneous and random distribution of CNTs in these nanocomposites, we interpret these results as arising from the LC-CNT surface interaction pinning the orientational order uniformly along the CNT, without pinning the position of the 9OO4 molecule, leading to a net ordering effect for all phases. These effects of incorporating CNTs into LCs are likely due to "anisotropic orientational" coupling between CNT and LC, the change in the elastic properties of composites and thermal anisotropic properties of the CNTs.

全漏光导波技术确定液晶材料的挠曲电系数

The fully-leaky optical guided wave technique was employed to measure the sum of splay and bend of flexoelectric coefficients in the negative nematic liquid crystal MS-N01300-000. The curves of reflectivity versus the internal angle (the angle of incident light to liquid crystal) with different flexoelectric coefficients under the same value of voltage can be calculated by the elastic theory of liquid crystal and the multi-layer optical theory. The director profile of the mentioned liquid crystal parameter filled in hybrid aligned nematic liquid crystal cell for different external applied voltages can be reflected by the curves of reflectivity versus the internal angle using the fully-leaky optical guided wave technique experimentally. There is a small move for the curves of reflectivity versus internal angle when alternating current voltage or direct current voltage with the same value is applied to the hybrid aligned nematic liquid crystal cell, which is induced by the flexoelectricity of liquid crystal. The approximate value of the sum of splay and bend of flexoelectric coefficient of MS-N01300-000 is 2.510-11 C/m by comparing theoretical results with experimental data.

FFS‐mode OS‐LCD for reducing eye strain

AbstractIn order to reduce eye strain, a driving method for reducing flickers of liquid crystal display (LCD) is devised. For this driving, an oxide semiconductor (OS) is used in a backplane, liquid crystal and alignment layer materials are optimized, and a fringe field switching (FFS) mode with a structurally formed storage capacitor is used. This work reveals that suitable usages of positive and negative liquid crystals differ from each other according to their characteristics. This work also describes an OS‐LCD with a touch sensor we fabricated for mobile devices, which proves the possibility of reducing‐eye‐strain technology (REST) with reduced flickers.

Effects of carbon nanotubes on electro-optic characteristics in vertically aligned liquid crystal display

Size- and aggregation-controlled dispersion of thin multiwalled carbon nanotube (t-MWCNT) in negative dielectric anisotropic liquid crystal (LC) material exhibits remarkable improvement in electro-optic response time in vertically aligned LC cells. The physical properties such as birefringence, dielectric anisotropy and clearing temperature of nanotube dispersed LC material appear to be almost invariant to that of pristine LC. Nevertheless, the response time shows noticeable improvement, especially in decaying time associated with transition from maximum to minimum transmission, hence important for faster switching LC devices. The effect is attributed to that vertically aligned t-MWCNTs along the field direction play role of vertical alignment layer between LCs, consequently resulting in increased bend elastic constant of LCs.

In-plane switching of vertically aligned negative liquid crystals for high transmittance and wide viewing angle

We propose a method for in-plane switching of vertically aligned negative liquid crystals (LCs) for high transmittance and wide viewing angle. By applying an in-plane electric field using a double-layered electrode structure, LC molecules can be rotated by the vertical as well as the in-plane components of the applied field over the entire region so that high transmittance can be achieved. The threshold voltage difference can be obtained simply by varying the electrode structure, which can reduce the off-axis gamma shift in a multidomain vertical alignment LC cell.

P.103: High Transmittance LC Mode Based on Fringe Field Switching of Vertically‐Aligned Negative LCs

AbstractIn this work we propose a liquid crystal mode in which vertically‐aligned negative nematic liquid crystals are switched on by applying a fringe electric field. In the proposed mode, vertically‐aligned negative liquid crystals can be switched on by the vertical as well as in‐plane components of an applied fringe field so that high transmittance can be achieved. By fabricating a test cell, we experimentally obtained a transmittance of 33.7 %, which is 8.7 % higher than a homogeneously‐aligned fringe field switching cell using positive liquid crystals.

扭曲排列增强的广视角技术

A new wide viewing angle liquid crystal device was developed using PET technology.The liquid crystal molecule was twisted by double electric field.The rising time of the design with negative liquid crystal is slightly greater than the positive's,and the falling time is accordance with the positive liquid crystal.Compared with positive liquid crystal,the transmittance is increased about 10%.The relationship of transmittance with response time and voltage,was analyzed in the effect of three electrodes.The wide viewing angle technology monopoly of FFS and IPS was effectively solved.

含有2,3,5,6-四氟亚苯基的负性液晶合成及液晶性研究

Two kinds of fluorinated negative liquid crystal compounds were synthesized.Two series of nematic liquid crystals were measured by polarised optical microscopy with a heating stage and differential scanning calorimetry and their good mesomorphic properties were observed.For example,the negative liquid crystals introducing 1,4-perfluorophenylene to molecular structure of diphenyl acetylene have high birfringence and low rotational viscosity.The result shows that the liquid crystal compounds with ethylidene bridge could have low birfringence and low viscosity.The first type of compounds could be used in adaptive system like as application in construction of spatial light modulator;the second type of compounds could satisfy the requirements of a low viscosity component in TFT-LCD.Two target compounds were synthesized by sonogashira coupling reaction and then Pd/C catalytic hydrogenation.

含链端烯基负性液晶单体的合成及其性能研究

Terminal alkeny-bearing liquid crystal compounds has been used in TN,STN,TFT and many other kinds of types of liquid crystal mixture,due to its advantages of solubility with other liquid crystals,low viscosity(especially low rotary viscosity γ1),but its synthetic difficulty is greater.This paper reports a modified synthetic method for the synthesis of terminal alkeny-bearing,lateral fluoro-benzene negative liquid crystals via the cross-coupling reactions of allyl chloride grignard reagent with substituted benzyl chlorides,which has high yields and low-cost.The liquid crystal characteristics of the prepared compounds are also investigated.

双环己基含氟二苯乙炔类负性液晶的合成及应用

双环己基含氟二苯乙炔类负性液晶的合成及应用

Measurement of nematic liquid crystal splay elastic constants by disclination line motion in high pretilt, negative dielectric anisotropy pi-cells

Negative dielectric anisotropy nematic liquid crystals confined to high pretilt pi-cells undergo a discontinuous, disclination mediated transition between a splayed and a twisted director configuration. A critical voltage, Us, exists at which the two states are in equilibrium and hence the movement of disclination lines ceases. We show that measurement of Us provides a simple and convenient means to determine the splay elastic constant, K11, of the liquid crystal to an accuracy of 10% or better.

Holy balls! Balls that walk on water

Related Articles Surface limitations to the electro-mechanical tuning range of negative dielectric anisotropy cholesteric liquid crystals J. Appl. Phys. 111, 063111 (2012) The effect of surface alignment on analog control of director rotation in polarization stiffened SmC* devices J. Appl. Phys. 109, 054108 (2011) Peculiar surface behavior of some ionic liquids based on active pharmaceutical ingredients J. Chem. Phys. 134, 074702 (2011) Stability in the memory state of the silica nanoparticle-doped hybrid aligned nematic device J. Appl. Phys. 109, 023505 (2011) Density functional theory of liquid crystals and surface anchoring: Hard Gaussian overlap-sphere and hard Gaussian overlap-surface potentials J. Chem. Phys. 133, 244701 (2010)

Achieving high light efficiency and fast response time in fringe field switching mode using a liquid crystal with negative dielectric anisotropy

The fringe-field switching (FFS) mode has been widely applied in high-resolution portable liquid crystal displays because of its excellent performances in transmittance, viewing angle, and operating voltage. Up to now, the FFS mode utilised a liquid crystal with positive dielectric anisotropy owing to fast response time and low operating voltage. This paper proposes a merit of using a liquid crystal with negative dielectric anisotropy. The optimised cell structures with thin cell gap and fine patterned electrode structures make the FFS mode with negative liquid crystals exhibit higher transmittance than that of the positive liquid crystals and a fast response time.

Experimental study of influence of external electric field on the photonic band gap of chiral liquid crystals

Influence of an external electric field on the boundaries of photonic band gap of a chiral liquid crystal has been studied experimentally. It is shown that by using a negative chiral liquid crystal and homeotropic boundary conditions one can increase the abruptness of photonic band gap boundaries and control thus the band gap width by application of the external electric field.

Surface limitations to the electro-mechanical tuning range of negative dielectric anisotropy cholesteric liquid crystals

Recent work on negative dielectric anisotropy cholesteric liquid crystals (CLCs) showed that externally applied dc voltages resulted in blue tuning of the reflection band position up to 20% of its original position. These results also showed that the observed shift in reflection band position was not caused by a direct interaction between the CLC and the applied voltage, but indirectly through electromechanical stresses that deformed the conductive glass substrates, in turn deforming the liquid crystal. In this work, the goal is to clarify that the major limiting factors on the tuning range limit result from the magnitude of the surface anchoring energy and surface induced hysteresis effects. An analytic solution for the tuning range limit and its dependence on the surface and bulk properties is derived that agrees well with the experimental data. Using this model, it was shown that tuning range limits in excess of 35% of the notch position should be expected with typically available alignment materials, and that with proper CLC/surface optimizations, values in the range of 75% are possible.

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.

A new negative liquid crystal lens with multiple ring electrodes in unequal widths

This study is dedicated to the design of a new negative liquid crystal (LC) lens with multiple ring electrodes in unequal widths. The number and widths of the multiple ring electrodes are designed to offer online tunability on focusing length by predetermined individual electrode voltages. This aims to render a smooth refraction index distribution that mimics well a divergent lens based on the theory of a gradient refraction index (GRIN) lens. Finally, the proposed negative LC lens is fabricated with the capability of realizing different focus lengths in a relatively large aperture of 5 mm and a thickness of 0.7 mm. Experiments are conducted to verify expected light-diverging performance. The effective focus length (EFL) is measured based on interference patterns. It is shown that the proposed negative LC lens is able to realize light-divergent effects with an EFL as short as -357.9 mm.

Study of Optical Bounce According to Electrode Structure in the Fringe-Field Switching Mode Using the Negative Liquid Crystal

The switching response behavior of negative dielectric anisotropic liquid crystal in the fringe-field switching (FFS) mode was investigated with respect to the pixel electrode positions. When the applied voltage relaxes to lower voltage, optical bounce was observed at the edge region of pixel electrode. Based on the simulation results, we have proposed a promising molecular behavior associated with optical bounce, which originates from the reorientation process of LC director that is in over-twist state associated with tilt angle. Experimental results also show the optical bounce during switching-off time.