Ferroelectric liquid crystal polymers

Verrall, Mark Andrew (1999) Ferroelectric liquid crystal polymers. University of Southampton, Doctoral Thesis.

Abstract

The molecular structural requirements for ferroelectric electro-optic switching in a side group liquid crystal poly(acrylate) were investigated. A range of side group poly(acrylate)s was synthesised and studied in thin (2μm) cells under applied electric fields. Electroclinic, ferroelectric and antiferroelectric switching were observed depending on the molecular structure of the polymer side groups, and the mesophase behaviour which they displayed.

A method for controlling the degree of polymerisation in the solution-based preparation of a number of side group poly(acrylates) was devised, allowing formation of polymers ranging in degree of polymerisation from less than ten, to several hundred repeat units. The physical properties of a number of side group poly(acrylates) with a broad range of molecular weights were assessed, and electro-optic assessment of ferroelectric side group polymers was attempted. However, high molecular weight examples could not be filled into thin electro-optic cells due to their high viscosity. A method for their preparation in-situ within thin cells was therefore devised, involving UV photo-polymerisation of acrylate monomers. The polymers formed in this way were shown to have extremely high molecular weights, and very slow electro-optic response speeds.

A liquid crystalline chain transfer agent was synthesised, and used to give reproducible and simple control of molecular weight in the UV photo-polymerisation process. Using this technique ferroelectric liquid crystal poly(acrylate)s with a range of molecular weight were prepared, and their electro-optic behaviour assessed. The switching temperature range and electro-optic response speeds were influenced strongly by the degree of polymerisation.

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