Chevron Layer Structure and Parabolic Focal Conics in Smectic A Liquid Crystals

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Abstract
The smectic A layer structures of homogeneously aligned 8CB and 4O.8 liquid crystals have been studied by X-ray diffraction analysis. It has been confirmed that the homogeneously aligned SmA cell is frequently characterized by the chevron layer structure with an array of elongated parabolic focal conics or by the tilted layer structure with the undulation pattern texture. This behavior is caused by the layer thinning and is generally affected by the cell thickness. The layer tilt angle of the chevron structure often depends on a phase sequence and a thermal history; for example, when a homogeneously aligned 4O.8 cell has cooled down to a SmB phase from a SmA phase, the layer tilt angle in the SmA phase in the heating process becomes two times larger than that in the cooling process.