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Title: Electro-optic studies of bistable smectic A organosiloxane liquid crystals
Author: Gardiner, D. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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This thesis examines the material and electro-optic characterisation of organosiloxane liquid crystals; these materials, by virtue of their chemically distinct, tri-block structure possess wide smectic A (SA) phases. They include one monomesogenic series, which consists of a 4-(ω-alkyloxy)-4’-cyanobiphenyl unit terminated by pentamethyldisiloxane and two bimesogenic series, which consist of twin 4-(ω-alkyloxy)-4’-cyanobiphenyls joined via tetramethyldisiloxane or decamethylpentasiloxane. It is shown that these liquid crystals possess highly anisotropic conductivity, with the ratio of the conductivities parallel (σ||) and perpendicular (σ) to the director as low as σ||/σ ~ 0.005. For typical smectic A materials e.g. 4-octyl-4’-cyanobiphenyl (8CB) this value is 0.5. It is also demonstrated that a typical value of the dielectric anisotropy, Δε, is ~ 1, which is significantly less than other SA materials e.g. 8CB and Δε ~ 8.4. These material properties are explained in terms of the structure generated by these materials; the microphase separation of the siloxane units restricts ionic flow parallel to the director; the reduced Δε is explained in terms of increased anti-parallel correlation of molecular dipoles. These properties explain the unusual electro-optic results, in an electrically addressed bistable smectic A display, in that the threshold voltage of one mode, the clear to scattering transition (write), was approximately 0.5 that of the other mode, scattering to clear (erase). For 8CB, this ratio is typically 2.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available