Amount Of Chiral Dopant Research Articles

One-dimensional model for simulating blue-phase liquid crystal display

ABSTRACTWe proposed a one-dimensional model for simulating some performances of blue-phase liquid crystal (BPLC) and polymer-stabilised blue-phase liquid crystal (PSBPLCD). The one-dimensional model treats liquid crystal arrangement of BPLC as cholesteric liquid crystal with high and uniform tilt angle to simulate the Bragg reflection of BPLC. The simulated results agree quite well with the experimental results. The elastic and dynamical equations are formed to calculate the effective elastic parameters and the response times of PSBPLCD. The effective elastic parameter is a constant for low electric field and decreases with the increasing of electric field. The varied effective elastic parameter means the varied restoring force of liquid crystal under the electric field. The dynamical equations are proposed to calculate response times, and the response mechanism of BPLCD is discussed by researching the difference between the decay times from equation and experiment. The sub-millisecond response time results from the weak anchoring of polymer network or the increasing of rotational viscosity of PSBPLC with high-concentration monomer, and the reason of 10 µs response time is the strong anchoring and small amount of chiral dopant and monomer.

Optically isotropic liquid crystals for next-generation displays

LCDs have become indispensable in our daily lives. They are used everywhere, such as in cell phones, computers, television sets, and data projectors. Based on continuous innovation, their overall display quality has reached a satisfactory level. Viewingangle restrictions are no longer an issue following implementation of multidomain structures and phase-compensation films, their contrast ratio has exceeded onemillion to one through local LED-backlight dimming, and sunlight washout has been overcome by employing transflective displays. LCD technology is, thus, relatively mature. However, some challenges still remain, including their relatively slow response time. This causes image blur for fast-moving objects and holds back adoption of colorsequential displays, which promise to triple light efficiency and resolution density. Much effort has been devoted to improving LCD response times. With continuously improving low-viscosity liquid-crystal (LC) properties, device configuration, and driving methods, the response time has been reduced to 2–5ms.1 However, it is still not fast enough to eliminate the color breakup observed in colorsequential displays. Suppressing this phenomenon requires LC response times of less than 1ms. To achieve this goal, optically isotropic LC is emerging as a potential next-generation display technology. A conventional, nematic LC turns isotropic when the temperature exceeds the clearing point. Within a few degrees above the nematic-isotropic transition temperature, LCs can still be controlled by an electric field and exhibit 100ns response time.2 However, the remaining phase is too small and the required operating voltage too high for display applications. By introducing a certain amount of chiral dopant and polymers into a LC host, polymer-stabilized LC composites can be made optically isotropic over a reasonably wide temperature range.3 Compared to conventional, nematic LCDs, this new optically isotropic LC exhibits several advantages. First, the system can be Figure 1. Optically isotropic liquid crystals (LCs) in an in-planeswitching electrode cell. Left/right: Voltage-off/on. P: Polarizer. A: Analyzer. E: Electric field.

Effects of cell parameters on the properties of hybrid twisted nematic displays

This article presents the results of an investigation of the electro-optical response for a hybrid twisted nematic (HTN) liquid crystal display. The device used both a hybrid alignment and a twisted director configuration. In comparison with the conventional twisted nematic mode, a faster response and a smaller operation voltage were obtained by using an appropriate amount of chiral dopant. The characteristics of the HTN cells were dependent on cell parameters such as the chemical nature of the polymer alignment layer, the cell thickness, the set twist angle, and the concentration of chiral dopant. Response times of 1.0 ms for turn-on and 16 ms for turn-off were achieved by the regulation of cell parameters. Computer simulations of the director configuration demonstrated that twist deformation plays an important role in the determination of the response characteristics.

Effect of chiral dopant on a helical Sm1 phase of banana-shaped N-n-O-PIMB molecules

The chiral helical structures of the Sm1 phase of naphthalene-2,7-diyl bis[4-(4-alkoxyphenyliminomethyl)benzoates] (N-n-O-PIMB) occur with equal probability for right- and left-handed structures. In this report, we investigated the effect of chiral dopants on the formation of these structures. Two chiral homologues, N-4-O-PIMB2* with (S)-(+)-2-methylbutoxy tails and N-8-O-PIMB6* with (S)-(+)-6-methyloctyloxy tails, were synthesized for this purpose. We found that the chiral agent induces an imbalance between the two chiral domains such that the area of one of the two domains increases with chiral dopant content. The position of the chiral centre of the doping agent plays an important role in controlling the helical sense as well as the strength of the effect. A stronger effect was observed for N-4-O-PIMB2* in which the asymmetric carbon is closer to the central core. The helical pitch is not affected by the amount of chiral dopant as observed from the wavelength maximum in the CD curve. Further, it is interesting that N-4-O-PIMB2* induces preferentially left-handed helical structures, while N-8-O-PIMB6* forms right-handed structures. These unusual effects of the chiral dopant are discussed with a comparison with the conventional chiral phases such as the chiral nematic and SmC phases.

Effect of Chiral Dopant Concentration on the Time Response of a Twisted Nematic Cell

Abstract The dependence of the turn-off time, T off, of a twisted nematic cell on the cell thickness and the chiral dopant concentration has been measured. T off dropped and the optical bounce disappeared when the cell thickness exceeded p/2, where p is the induced pitch length. Under these conditions a 3π/2 cell was obtained. It appears possible, on the basis of our results, to reduce the temperature dependence of T off by adding the correct amount of chiral dopant.