The realignment of an achiral smectic C chevron structure with applied field

This is the second of two papers describing the study of a conventional display cell filled with an achiral smectic C phase. In our first paper we described the X-ray diffraction study of the smectic layer alignment in the cell in its initial 'off' state. The mesogen used has positive dielectric anisotropy and the cell surfaces were treated conventionally to give a parallel homogeneous alignment. The X-ray results were interpreted in terms of a complex three-component chevron pattern with two outer arms and a central, tilted bookshelf region. This paper concerns the change in optical texture of the cell as the applied field is increased. There is a sequence of reversible texture changes before the final irreversible breakdown of the structure. The optical data are consolidated by electro-optic and field-dependent X-ray data. We interpret the changes in optical texture in terms of a sequence of four distinct realignment processes as the field is increased: (I) re-alignment of the molecules within the existing layer structure by rotation of the director around the smectic C cones; (2) growth of the two outer chevron arms at the expense of the central bookshelf region; (3) a progressive modification of the domain structure; (4) an abrupt, drastic, irreversible re-alignment at high field with complete breakdown of the original chevron structure to a quasi-homeotropic structure.