New liquid crystals with very low viscosity, good mesophase behavior, and high reliability are necessary to achieve the breakthrough from flat computer monitors to large displays for television. Fluorine plays a decisive role not only because of the polarity it induces in organic molecules but also because of its low polarizability and weak propensity for ion solvation. In addition, subtle stereoelectronic effects in fluorine-containing liquid crystals influence material properties and allow these to be tuned to some extent to achieve the desired outcome. Some fairly sophisticated chemistry is required that is normally ruled out in the specialty chemicals industry because of cost. The television display market is now entering a phase of saturation. The broad availability of the internet has led to an ever increasing tendency for mobile products. Tablet PCs and smartphones require touch-panel functionality and low power consumption. New LCD modes with high-performance liquid crystals and additional components, such as polymerizable materials, can be used in such products.
We report the observation of the smectic A
F
, a liquid crystal phase of the ferroelectric nematic realm. The smectic A
F
is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10
5
V
/
m is observed. The SmA
F
phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z
A
(SmZ
A
)–ferroelectric nematic (N
F
)–SmA
F
phase sequence, and 7N/DIO, exhibiting an N–SmZ
A
–SmA
F
phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.
Electro-optical switching of the liquid crystalline Blue Phase exhibits extremely fast response times. However, the unstabilized Blue Phase is characterized by a rather narrow temperature range on the order of a few K. For display applications the operating temperature range needs to be increased. One very promising way is to broaden the stable temperature range by polymer-stabilization of the Blue Phase. Successful stabilization is achieved by proper material selection/matching of reactive mesogens (RMs) and the chiral host. One prerequisite for application in display manufacturing is excellent UV and heat stability as well as good processability. Improvements in relevant performance parameters will be presented and discussed. Fig. 1 Principal constituents of a Blue Phase (BP) mixture include the nematic host mixture, chiral dopant and monomers. 4.4 / M. Wittek SID 2012 DIGEST • 25 ISSN 0097-966X/12/4301-0025-$1.00
Abstract—
Notebook applications have been one of the most important driving forces behind the remarkable growth of liquid‐crystal displays (LCDs). LCDs have recently been well accepted in the monitor market and large growth is forecasted because of the replacement of CRTs. The next challenge for LCDs is the TV market. These new application areas are supported by advanced LC technologies such as film‐compensated twisted nematic (TN), in‐plane switching (IPS), and vertically aligned (VA) modes. Each TFT technology requires a corresponding LC material improvement. We will review the recent liquid‐crystal material development for these advanced LC technologies.
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