Patrick Nolan

High on-state clarity polymer dispersed liquid crystal films

Abstract Results are presented which show that the on-state clarity of a UV cured polymer dispersed liquid crystal (PDLC) film depends on the refractive index of the final polymer in the PDLC film, the ordinary refractive index of the liquid crystal, the solubility of the liquid crystal in the prepolymer and the rate at which the film is cured. Liquid crystal mixtures for use in PDLC films are chosen such that the ordinary refractive index of the liquid crystal is equal to the refractive index of the polymer matrix. It has been shown previously that a large quantity of liquid crystal remains dissolved in the polymer matrix, thus increasing the mismatch between the refractive index of the polymer and the ordinary refractive index of the liquid crystal and therefore reducing the on-state clarity. For liquid crystal mixtures which have high solubility in the prepolymer (>60 per cent) the mismatch in the refractive indices can be very large and the on-state clarity of the resulting film can be very poor (T on...

Recent developments in materials for TFT/PDLC devices

Liquid crystal mixtures for use over an active matrix substrate must have a high resistivity and, to maintain high value during the lifetime of the display, the materials must be very stable. Many such liquid crystal mixtures are known and used in twisted nematic displays but they are of low birefringence; very few high birefringence liquid crystals of this type are known. Several classes of liquid crystal which fulfill these criteria have been developed and formulated into low melting point mixtures suitable for use with UV curing prepolymers. The properties of PDLC films containing these new mixtures show that the high birefringence values now possible can lead to substantially increased contrast ratios.

Film-formation parameters affecting the electro-optic properties of low-voltage polymer-dispersed liquid crystal (PDLC) films

Polymer dispersed liquid crystals have received much attention recently due to their potential applications in projection and direct view displays. In this paper, the effect of curing conditions, i.e., UV lamp power, exposure time and curing temperature, on the electro-optic properties of PDLC films are reported for both direct view and projection applications. The variation of electro-optic properties with variation of film thickness for different liquid crystal mixtures is also reported. The results presented indicate that an optimum curing temperature and lamp power exist at which an optimum contrast can be achieved for a given film thickness.