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1. A thermotropic liquid crystal smectic A composition exhibiting a smectic type A phase made up of multiple layers and capable of forming a liquid crystal optical device when sandwiched between a pair of electrodes, wherein:
under the influence of different electric fields applied between the electrodes, the alignment of the layers of the composition can become more ordered or more disordered, and the composition has stable states in which the alignment of the layers of the composition are differently ordered including an ordered state, a disordered state, and intermediate states, the composition being such that, once switched to a given state by an electric field, it remains substantially in that state when the field is removed, which composition comprises, in weight %: (a) 25-75% in total of at least one siloxane of the general formula I: wherein
p=1 to 10,q=1 to 12,t=0 or 1,k=2 or 3,A is a phenyl or cyclohexyl ring which may be the same or different and are bonded together in para positions,R=a C1-3 alkyl group, which may be the same or different,X=a C1-12 alkyl group, andZ=F, Cl, Br, I, CN, NH2, NO2, NMe2, NCS, CH3, or OCH3, CF3, OCF3, CH2F, CHF2; (b) 0.001-1% in total of at least one quaternary ammonium ionisable species of the general formula II: wherein:
T=a methyl group or a silyl or siloxane group, andv=1 to 30,R1, R2, and R3, which may be the same or different, are C1-4 alkyl,Q− is an oxidatively stable ion, (c) 20-65% in total of at least one polarisable linear molecule having an alkyl chain, the molecule having the general formula III:
D-A′k-Y (III)wherein:D stands for a C1-16 straight chained alkyl or alkoxy group, optionally containing one or more double bonds;k=2 or 3,A′ is a phenyl, cyclohexyl, pyrimidine, 1,3-dioxane, or 1,4- bicyclo[2,2,2]octyl ring, wherein each A′ may be the same or different and are bonded together in para positions, the terminal ring attached to Y optionally being a phenyl, andY is located in the para position of the terminal ring of the group A′k and is selected from Z (as defined above in connection with Formula I), C1-16 straight chained alkyl, C1-16 straight chained alkoxy, OCHF2, NMe2, CH3, OCOCH3, and COCH3; and (d) 2-20% in total of at least one side chain liquid crystal polysiloxane of the general formula IV: wherein:a, b, and c each independently have a value of 0 to 100 and are such that a+b+c has an average value in the range 3 to 200, and a is such that the chain units of the formula Y—R2SiO—[SiR2—O]a represents 0 to 25 mole percentage of the compound of the general formula IV, and c is such that the units of the formula chain —[SiHR—O]c—R2SiO—Y represents 0 to 15 mole percentage of the compound of the general formula IV,m=3 to 20t=0 or 1,k=2 or 3,A is a phenyl or cyclohexyl ring which may be the same or different and the rings are bonded together in para positions,R=a C1-3 alkyl group each of which may be the same or different, andY=a C1-12 alkyl group, a chromophore, or a calamitic liquid crystal group and each of which may be the same or different, andZ is as defined above in connection with Formula I, and wherein the amounts and nature of the components are selected such that the composition possesses smectic A layering and siloxane-rich sub-layering, as detected by X-ray diffraction. |
