Liquid Crystal Formulations And Structures For Smectic A Optical Devices

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, and
• Z═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 salt of the general formula II:
• wherein:
• T=a methyl group or a silyl or siloxane group, and
• v=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, and
• Y 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 20
• t=0 or 1,
• k=2 or
• 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,
• and
• Y=a C1-12 alkyl group, a chromophore, or a calamitic liquid crystal group and each of which may be the same or different, and
• Z 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.