Pretilt angle inducing mechanisms and surface-stabilized ferroelectric liquid crystals

Abstract

We have investigated the role of fluorine containing groups and of alkyl side chains in the generation of pretilt angles. From X-ray photoelectron spectroscopy it was concluded that the fluorine-containing groups force the polyimide to adapt a certain conformation and that this conformation governs the pretilt angle. The effect of alkyl side chains was studied by modification of the surface of poly(vinylalcohol) with alkanoyl chlorides. The pretilt angle was found to depend on the length and surface density of the grafted chains. A uniform and tilted orientation could only be obtained by grafting long alkyl chains. The influence of the pretilt angle on the effective cone angle in ferroelectric liquid crystals has been calculated and was found to agree reasonably well with the experimental values. Angles between the memory states of 40° have been obtained leading to brightness levels comparable to those of the twisted nematic effect.