Observation of a chevron hybrid structure in the smectic A phase of a liquid crystal device

Abstract

Small angle X-ray diffraction experiments show the emergence of a chevron structure on cooling from the nematic phase into the smectic A phase of the commercial mixture S3 (Merck Ltd, UK), in a display device. The chevron angle increases from 0° at the nematicsmectic transition temperature, T _NS, to a maximum value of 8.5°, which is reached when the sample is 15°C below T _NS. Between 5°C and 15°C below the transition temperature a quasi bookshelf structure emerges, in addition to the prevailing chevron structure; such a structure has not been hitherto reported. There is no further resolvable change in the device structure on cooling lower than T _NS-15°C. The chevron structure is due to the combination of layer thinning and fixed surface layers, as confirmed by a comparison of layer spacing calculated from the Bragg angle equation and from the layer thinning equation (d=d ^nematiccosδ, where δ is the chevron angle).