Compositions – Radioactive compositions – Nuclear reactor fuel
Patent
1986-08-19
1989-08-01
Gron, Teddy S.
Compositions
Radioactive compositions
Nuclear reactor fuel
25229901, 25229966, 25229963, 25229961, 25229965, 25229962, 560 59, 560102, 350350R, G02F 113, C09K 1912, C09K 1952, C09K 1930
Patent
active
048529770
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to derivatives of .alpha.-hydroxy carboxylic acids suitable for use in liquid crystal materials and devices.
In particular the invention relates to ferroelectric liquid crystal materials, which show a tilted chiral smectic liquid crystal mesophase. Such materials have been proposed for use in rapidly switched electro-optical devices, for example processing and storage devices and displays, based on the ferroelectric properties of the material in the titled chiral smectic phase, eg as described by N A Clark and S T Lagerwall in `App Phys Lett` 36 P899, (1980) (Reference 1).
A measure of the effectiveness of a ferroelectric liquid crystal material is its spontaneous polarisation coefficient Ps. It is desirable to have as high a Ps as possible in a ferroelectric liquid crystal material for electro-optical applications, whilst also combining this high Ps with the other desirable properties generally sought in liquid crystal materials eg low viscosity, broad liquid crystal phase range, stability etc. The tilted smectic phases which exhibit ferroelectric behaviour are the chiral C, F, G, H, I, J, and K phases (designated hereinafter as S*.sub.C, S*.sub.F etc, the asterisk indicating chirality). The S*c phase is most commonly sought as this is the most fluid. It is also desirable that the liquid crystal materials shows an S.sub.A phase at a temperature above its S* phase, as tjhis assists surface alignment in the device.
Although some liquid crystal compounds show S* phases embodying many of the desirable properties outlined above, it is common in practice to use a material which is a mixture of at least two components, or sets of components, ie a `host` which exhibits a smectic phase which may or may not be chiral, and a `dopant` which is mixed with the host to produce a tilted chiral smectic phase with a high Ps. The dopant may serve to improve other properties of the host or mixture to produce an advantageous ferroelectric mixture.
In contrast to research on nematic liquid crystals, relatively little is known about desirable molecular structures for S* compounds and materials. Many materials which are at present used in ferroelectric displays have low Ps values or are chemically unstable, such as the compounds DOBAMBCand HOBACPC described in Ref 1.
It is an object of the present invention to provide a new range of S* ferroelectric liquid crystal materials having improved properties. Other objects and advantages of the present invention will be apparent from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration defining the dopant's sense of polarization; and
FIG. 2 is a cross-sectional view of a liquid crystal cell.
DESCRIPTION OF THE INVENTION
According to the present invention there is provided a compound which may be used as a host or dopant in a ferroelectric chiral smectic liquid crystal mixture, the compound being a derivative of an .alpha.-hydroxy carboxylic acid containing the chiral unit: ##STR2## in which Ro represents alkyl, alkoxy, halogen, ##STR3## where b is 0 to 3 and the phenyl ring may be substituted with one or more alkyl, alkoxy, halogen or cyano groups and a may be 0 or 1.
In such a compound this unit is linked at both of the indicated termini to a combination of groups which are mesogenic, is promote the formation of smectic liquid crystal phases either in the compound itself, or in mixtures with other potentially smectic compounds.
The type of groups which are likely to be mesogenic are generally well known in liquid crystal chemistry and the combination of the above unit with a wide rage of mesogenic groups will provide the advantages discussed below.
Some particularly advantageous combinations have been discovered, and therefore according to the present invention in a second aspect there is provided a derivative of an .alpha.-hydroxy carboxylic acid having a formula: ##STR4## wherein X represents a group having a structure: --(A.sup.3 S.sup.3).sub.k --(A.sup.8 S.sup.8).sub.r -- A.sup.5).sub.m --(S.sup.4 A.sup.4).sub.1
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Gray et al., Liqiud Crystals & Plastic Crystals, vol. 1, pp. 140-141 (1974).
Chan Lawrence K. M.
Coates David
Gemmell Peter A.
Gray George W.
Lacey David
Gron Teddy S.
The Secretary of State for Defence in Her Britannic Majesty's Go
Thomas J. E.
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