Mark Verrall

The Influence of the Backbone on the Structure of Side-Chain Liquid Crystal Polymers

Abstract Structural investigations using X-ray diffraction on four side-chain liquid crystal polymers with the same mesogenic units but different backbones are described. An S*C phase was identified in all of them. Three of the polymers exhibit an unusual phase with a superlattice structure below this S*C phase. A simple model of the packing in this phase is proposed to explain the formation of the superlattice. The effects of varying the polymer backbone on the stability of this phase are also discussed.

Advances in LC display performance using optical films

New generations of large area liquid crystal displays require very high optical performance to compete with CRT and other emerging technologies. This performance must include high contrast ratio, high stability of all grey levels, and excellent colour reproduction, and typically this is requested for up to 80# viewing angles in all directions. Some potential difficulties to achieving wide viewing performance in single domain LCDs are discussed, with explanation for the advantages to multi-domain LC display. Finally we shall describe some new optical film developments which can be used to achieve the targets for high performance at all viewing angles combining multi-domain LC display, together with optical films prepared from reactive mesogens.

FERROELECTRIC SWITCHING LIQUID CRYSTAL POLYACRYLATES - THE CONTROL AND EFFECT OF MOLECULAR WEIGHT

Abstract The polymerisation of two liquid crystalline acrylate monomers is discussed with particular reference to control of the degree of polymerisation. Two series of liquid crystalline side chain polymers are produced, each with a broad smectic C phase and with a range of molecular weights. The electro-optic behaviour of the materials is discussed, and in one of the series ferroelectric response to electric field is observed for all molecular weights. This includes a sample with a very high degree of polymerisation where the molecular weight is too high to allow dissolution in tetrahydrofuran, and therefore cannot be measured by gel permeation chromatography.

FERROELECTRIC LIQUID CRYSTALLINE COPOLYACRYLATES - THE CONTROL OF PHASE BEHAVIOUR AND SWITCHING

Abstract The synthesis of two side group liquid crystalline polyacrylates is discussed, one bearing a biphenyl benzoate core structure, and the other a phenyl benzoate core. The three-ring variant displays electroclinic and ferroelectric switching, but the desired ferroelectric switching occurs only at temperatures greater than ≈50°C. The two-ring version displays only electroclinic behaviour, but the response can be observed even at room temperature (25°C). The copolymerisation of the two monomers is presented across a range of percentages, and the desired ferroelectric switching range is modified throughout the series to promote ferroelectric switching at room temperature.

Unusual Odd-Even Effects in Vinyl Ether and Acrylated Direactive Liquid Crystals

Abstract Four series of direactive liquid crystals are presented and their physical properties characterised. The core groups are based on either a lateral chloro or methyl terphenyl and the reactive groups are either acrylates or vinyl ethers. It is shown that reactive liquid crystals with vinyl ether reactive groups have higher transition temperatures, birefringence, and order parameter than the corresponding acrylates. Both the vinyl ether and acrylate series show an odd-even effect in transition temperatures, birefringence and order parameters. The odd-even effect in the vinyl ether series is particularly marked.

The laser exposure requirements of liquid crystal polymer thin films for photomasking applications

Thin solid films of a cyanobiphenyl based polymethacrylate liquid crystal polymer (LCP) coated onto quartz substrates have been thermally processed to give a UV light scattering texture for use as a photomask opaque layer. UV transparent line patterns in the scattering layer may subsequently be written by scanning a focused laser beam across the LCP surface. The exposed linewidths are found to be strongly dependent upon the thickness of the LCP film, the incident power of the laser, and the overall residence time of the focused beam waist at a given location on the film surface. Successful exposure of the LCP films demands that the absorbed laser energy and beam waist residence time should exceed minimum threshold magnitudes however, and it is demonstrated that the smallest feature size which may be defined in the scattering layer is effectively limited by heat conduction from the LCP to the quartz substrate. Possible approaches towards improving the exposure requirements of the LCP are considered, and the compatibility of the proposed LCP photomask with current industrial direct-write laser systems is appraised.

Layer structure in processed ferroelectric side-chain liquid-crystal polymers

Abstract Our investigations of the local smectic layer distribution formed by two ferroelectric side-chain liquid crystal polymers in device-like environments are described. At room temperature one of the polymers had a bookshelf distribution of its smectic layers. The addition of one methylene unit to the flexible spacer resulted in a different phase behaviour which included an overall decrease in the measured smectic periodicity. The local layer structure displayed by this polymer in the same device-like environment at room temperature was characterised by a chevron geometry.