12 April 2005 Optimization of organosiloxane mesogenic properties for use in a smectic-A display
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Organosiloxane liquid crystals have previously been shown to have much potential in bistable smectic-A devices; in this paper we aim to optimise the device performance by reducing threshold voltages and response times. Our results show that mixtures of novel organosiloxanes with enhanced dielectric coupling can significantly these key parameters. The molecules used were of the A/B and A/B/A type, where B refers to the number of siloxane units, and A to the mesogenic unit(s) attached. The molecule 5/2, which has a pentamethyldisiloxane (PMDS) group laterally attached to a pentyl-oxycyanobiphenyl (5OCB) mesogenic unit, was chosen as host for the mixtures. Of the A/B type, two napthylene-core molecules were chosen, which are designated Si2-4-ONEBN and Si3(iso)-4-ONEBN. These molecules have identical cores and alkyl chain lengths but differ in the number and conformation of the siloxane moiety. Of the A/B/A type, 5/2/5 was selected. This molecule consists of two 5OCB units joined via a PMDS group. The concentrations used were 0.3 mol (A/B type) and 0.15 mol (A/B/A type). Threshold voltages of the mixtures were measured as a function of shifted temperature; the response times were measured at fixed temperature as a function of applied voltage. It was found that all the mixtures gave favourable results, with the 0.3 mole fraction Si2-4-ONEBN response times of 20 ms were achieved - an order of magnitude faster than pure 5/2. Threshold voltages were shown to be reduced by approximately 25% for all mixtures with no degradation in mesogenic behaviour.
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Damian J. Gardiner, Harry James Coles, "Optimization of organosiloxane mesogenic properties for use in a smectic-A display", Proc. SPIE 5741, Emerging Liquid Crystal Technologies, (12 April 2005); doi: 10.1117/12.593893; https://doi.org/10.1117/12.593893

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