Voltage reduction in twisted nematic liquid crystals by reverse (negative) doping

Nano P(VDF-TrFE) doped polyimide alignment layers for twisted nematic liquid crystal devices

The application of the Liquid Crystal Display (LCD) to TV application needs faster response time to reduce trailing effect of moving picture. Due to the strong anchoring energy of liquid crystals on the alignment layer, the overall response time is increased. Therefore the control of the anchoring strength of the Liquid Crystals at the surface layer in display device could improve the response time of LCD. From the previous research of various kinds of hydroxyl functional perfluorinated additives [1], we chose the monohydroxylated additives for further study. In this research the effects of degree of fluorination in additives on the performance of Liquid Crystal Displays were investigated for the structure-property relationship with respect to weak anchoring property. The overall electro-optical and physical properties were measured to determine the role of the additive in Liquid Crystal mixtures. The molecular structure of the additive was changed to impose different polarity and interaction with the Liquid Crystal and alignment layer. The additives reduced the operating voltage of host liquid crystal materials and produced a slippery surface without any phase separation.

Using image analysis techniques to enhance TFT-LCD manufacturing yield through timely detection of PI alignment layer defects

We studied the design rules of the reflective type liquid crystal display (LCD) and the retardation films in order to prevent the color shift and the change of the reflectance. By analyzing the polarized state of light after passing through the LCD, and excellent reflective LCD, which shows almost constant reflectance in wide viewing angle without color shift by using the twist liquid crystal cell.

In this paper, a flexible liquid crystal display (LCD) is developed by applying hybrid alignment layers made of vanadium dioxide (VO2) nanoparticles and homeotropic-polyimide (h-PI) onto colorless plastic substrates, and the proposed hybrid thin layers with randomly embedded agglomerated VO2 nanoparticles exhibit a transparency over 85% at 550 nm including the substrate and a strong surface irregularity. After rubbing, liquid crystals (LCs) are vertically aligned between the hybrid thin layers with a tilt angle of ∼90°, and due to the significant surface plasmon polariton (SPP) of VO2 nanoparticles, the switch of LCs under the external electrical field has been remarkably accelerated. The operating voltage to switch LCs in a 5 μm cell assembled using a pair of 0.5% VO2 nanoparticle doped h-PI hybrid alignment layers has been reduced to 3.536 V, and simultaneously, the decaying time is also shortened more than 18%. Notably, the vertical alignment of LCs was also stabilized under bending thanks to the use of undulating hybrid alignment layers. The fabricated flexible LC cell using 0.5% VO2 nanoparticle doped h-PI alignment layers yielded good flexibility at a bending radius of 1500 mm without aggravated light leakages and deduced electro-optical performance, and the VO2 agglomerates hindering the slide of LCs by providing adequate obstructions are believed as the main contributors in firmly stabilizing the vertical alignment of LCs during bending. Compared to micropatterned substrates, ultrathin VO2 nanoparticle doped h-PI alignment layers employed in flexible LC cells demonstrating their priorities in easy investigation and displaying quality improvement are emerging, highly appreciated, and of great interest for the potential applications in flexible LCDs.

Fabrication of homogenously self-alignment fringe-field switching mode liquid crystal cell without using a conventional alignment layer

In this paper we propose a new approach to fiber optic voltage sensors via voltage-controlled Liquid Crystals (LC), which would allow direct measurement of up to 400 kV/m electric fields at multiple points. In addition, the electro-optical behavior of deformed helix ferroelectric (DHF) liquid crystal in reflective mode is described and tested. The electrically controlled reflectance has been measured at sub-kilohertz driving voltage frequency for different polarizations of the incident light. Full Text: PDF References Y.V. Izdebskaya, V.G. Shvedov, A.S. Desyatnikov, W. Krolikowski and Y.S. Kivshar, "Soliton bending and routing induced by interaction with curved surfaces in nematic liquid crystals", Opt. Lett. 35, 1692-1694 (2010). CrossRef Z. Ge, S. Gauza, M. Jiao, H. Xianyu and S.T. Wu, "Electro-optics of polymer-stabilized blue phase liquid crystal displays", Appl. Phys. Lett. 94, 101104 (2009). CrossRef Z. Brodzeli, F. Ladouceur, L. Silvestri, A. Michie, V. Chigrinov, G. Q. Guo, E. P. Pozhidaev and A. D. Kiselev, "Liquid crystal-based hydrophone arrays", APOS (2012). CrossRef T. Tanigawa, Y. Sakakibara, S. Fang, T. Sekikawa and M. Yamashita, "Spatial light modulator of 648 pixels with liquid crystal transparent from ultraviolet to near-infrared and its chirp compensation application", Opt. Lett. 34, 1696-1698 (2009). CrossRef K. H. Yang and T. C. Chieu, "Transport Properties of Ions in Ferroelectric Liquid Crystal Cells", Jpn. J. Appl. Phys. 28, 2240-2246 (1989) CrossRef I.C. Khoo and S.T. Wu, "Optics and Nonlinear Optics of Liquid Crystals", World Scientific, Singapore (1993). V.G. Chigrinov, "Liquid Crystal Devices: Physics and Applications", Artech House, Boston: London, (1999). A.D. Kiselev, E.P. Pozhidaev, V.G. Chigrinov and H.S. Kwok, "Polarization-gratings approach to deformed-helix ferroelectric liquid crystals with subwavelength pitch", Phys. Rev. E 83, 31703 (2011). CrossRef N. A. Clark and S. T. Lagerwall, "Submicrosecond bistable electro-optic switching in liquid crystals", Appl. Phys. Lett. 36, 899-901 (1980). CrossRef L.A. Beresnev, V.G. Chigrinov, D.I. Dergachev, E.P. Pozhidaev, J. Funfshilling and M. Schadt, "Deformed helix ferroelectric liquid crystal display: A new electrooptic mode in ferroelectric chiral smectic C liquid crystals", Liq. Cryst. 5, 1171-1177 (1989). CrossRef Z. Brodzeli, H.K. Bal, V.G. Chigrinov, A. Murauski, and F. Ladouceur, "Electrical energy harvesting device for current/voltage fibre-based sensors", Optical Fibre Technology (ACOFT), 2010 35th Australian Conference on Fibre Technology, 1-2, (2010). DirectLink X. Zhao, F. Boussaid, A. Bermak and V.G. Chigrinov, "High-resolution thin ?guest-host? micropolarizer arrays for visible imaging polarimetry", Opt. Exp. 19, 5565-5573 (2011). CrossRef X.H. Li, A. Murauski, A. Muravsky, P.Z. Xu, H.L. Cheung, and V. Chigrinov, "Grayscale Generation and Stabilization in Ferroelectric Liquid Crystal Display," J. Display Technol. 3, 273-279 (2007). CrossRef E.P. Pozhidaev, S. Torgova, M. Minchenko, C. Yednak, A. Strigazzi and E. Miraldi, "Phase modulation and ellipticity of the light transmitted through a smectic C* layer with short helix pitch", Liq. Cryst. 37, 1067-1081, (2010). CrossRef E.P. Pozhidaev and V.G. Chigrinov, "Bistable and multistable states in ferroelectric liquid crystals", Crystallography Reports. 51, 1030-1040 (2006). CrossRef Q. Guo, F. Fan, T. Du, and V.G. Chigrinov, "Electrooptic Response of FLC: Effect of Alignment Materials", SID'11 Conference, P-144, Los Angeles, USA, May, (2011). CrossRef G. Hegde, P. Xu, E.P. Pozhidaev, V.G. Chigrinov, and H.S. Kwok, "Electrically controlled birefringence colours in deformed helix ferroelectric liquid crystals", Liq. Cryst. 35, 1137-1144 (2008). CrossRef

Photo-enforced stratification of liquid crystal / monomer mixtures : principle, theory and analysis of a paintable LCD concept

We have developed a method, using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), to directly analyze metal ion impurities in liquid crystals (LCs). From measurements of resistivity, a commonly used technique for quality control of liquid crystal display (LCD) cells, we found that the resistivities of the LCs decreased significantly upon progressing through the different stages of the LCD cell manufacturing process. We determined the levels of metal ion impurities in the LCs through direct loading of diluted LC samples into the HR-ICP-MS system at a steady flow rate. Solutions featuring LC contents of 10% (v/v) were formed by dissolving each LC in isopropanol (IPA) containing acetone as a modifier. We quantified the trace metal ion impurities in the LC samples using a certified standard of metal ions diluted in IPA (external calibration) without the need for digestion pretreatment. Next, we compared the levels of metal ion impurities with the resistivities of the LCs at the different stages of the LCD cell manufacturing process. We confirmed that the resistivities of the LCs decreased as the total levels of metal ion impurities in the LCs increased. The total content of metal ion impurities added into the LC was higher in the siphoning process than in the one-drop filling process during the fabrication of LCD cells. The HR-ICP-MS method could, therefore, be used to directly measure metal ion impurities in LCs during the LCD cell manufacturing process, potentially replacing resistivity measurements of LCs as a means of quality control. We suggest setting 1400 ng L−1 as the limit of the total metal ion concentration in LCs used for LCD cell manufacturing. We used the HR-ICP-MS method to analyze a stained LCD panel to confirm that the content of metal ion impurities was indeed significantly greater in the stained area of the defected LCD. HR-ICP-MS appears to be a promising technique for the direct and effective analyses of metal ion impurities in LCs.

The development of electrically tunable liquid crystal (LC) lenses is perspective and promising for a wide range of applications, for example, for imaging system, pico projectors, optical zoom systems, ophthalmology applications and other. Of particular note is the development of polarization-independent LC lenses, as eliminates polarizers from application devices that reduce the efficiency of light transmission through optical systems. Alignment benzaldehyde photosensitive materials, capable of changing the pretilt angles of nematic LC from 90 to 0 ºС in a controlled manner under UV exposure are developed. The anisotropy of the benzaldehyde alignment layers is generated by a two-stage treatment consisting of uniform rubbing with a cloth and subsequent non-polarized UV exposure. Inhomogeneous UV exposure of uniformly rubbed alignment layers allows formation of refractive index gradient inside the LC cell. The concept of tunable polarization-independent self-aligned LC lens based on gradient pretilt angle alignment materials with different photosensitivity is demonstrated. Self-alignment of two polarization-dependent sub-lens is achieved due to a single UV exposure act of two alignment layers, which are located on the same piece of glass on both sides, forming one common optical axis for a polarization-independent LC lens. The independence of the polarization of LC lenses is achieved by setting the azimuthal rubbing direction of the alignment layers of two polarizationdependent LC lenses perpendicular to each other. The sub-lens cells have uniform cell gap and are independently controlled using low-voltage driving. Devices based on gradient benzaldehyde alignment materials can be used in many modern optical and photonic devices.

Circularly polarized luminescent (CPL) materials featuring high luminescence dissymmetry factors (glum), high photoluminescence quantum yields (ΦPL), and tunable emission properties are essential for practical applications. Herein, three chiral aggregation-induced emission (AIE) tetraphenylbutadiene (TPB) derivatives (TPB-Chol*-H, TPB-Chol*-CHO, TPB-Chol*-OC6) with high ΦPL were synthesized, each bearing symmetric chiral bis-cholesteryl moieties and different electron-donating/accepting groups. When employed as chiral dopants, minute quantities of each derivative were individually doped into the achiral nematic liquid crystal (LC) 5CB, affording three series of luminescent chiral nematic LC composite systems (TPB-N*-LCs). These composites exhibit remarkable CPL activity with high glum values, attributed to host-guest interactions that facilitate co-assembly into ordered supramolecular helices and chiral amplification, despite the chiral AIE dopant itself lacking CPL emission. CPL signals and glum values enhance with increasing chiral dopant loading, peaking at +0.31, +0.42, and +0.58 for TPB-Chol*-H/5CB, TPB-Chol*-CHO/5CB, and TPB-Chol*-OC6/5CB, respectively, at 3 wt% doping. Notably, the introduction of electron-donating hexyloxy groups (TPB-Chol*-OC6) or electron-accepting aldehyde groups (TPB-Chol*-CHO) modulates molecular packing, compatibility with 5CB host, and intermolecular interactions. Doping TPB-Chol*-OC6 into 5CB achieves the optimal performance, with glum = +0.58 and ΦPL = 84.5%. This work offers an effective strategy for developing CPL materials with simultaneously high glum and ΦPL.

Time-dependent color simulation of active-matrix liquid crystal display adopting the field sequential driving method

Three in one: Mesogenic aromatic acid as a liquid crystal matrix, a chiral dopant in liquid crystals and a stabilizer for nanoparticles

Homogeneous liquid crystal alignment on poly(vinylidene fluoride-trifluoroethylene) films subjected to ion-beam irradiation

Vacuum pyrolysis characteristics and kinetic analysis of liquid crystal from scrap liquid crystal display panels