Nonchiral Smectic Liquid Crystals - Applications

This chapter is concerned with the application of both tilted and orthogonal smectic phases that do not contain a chiral center, within these constraints it is the smectic A phase (SmA) that is of most interest and has been most widely studied. 

The simple, popular picture of a smectic phase (Sm) consisting of elongated molecules in sharp, distinct layers is rather misleading a more realistic picture is one where the molecules are arranged to provide a single sinusoidal density wave [1] with its wave vector either parallel to the molecular director (orthogonal phases such as SmA, SmB, etc. - see Fig. 1) or at some angle to it (tilted phases such as SmC, SmI, etc.). However, it is often convenient to refer to the layered nature of the smectic phase to help explain phenomena such as conductivity anisotropy. 

In thin films, smectic phases can adopt one of several microscopic textures [2] depending on the preceding liquid crystal phase, the nature of the substrate (whether any aligning layer has been used), and on the type of smectic phase. Of particular relevance are the homeotropic and the focal conic textures shown by the orthogonal 

In some cases a combination of these techniques has led to a high tilt alignment [3]. 

It is energetically unfavorable to alter the layer thickness of the smectic phase, therefore any process that relies on this feature is very unlikely to occur. However, bending of the smectic layers is possible, because this need not cause a change in the layer thickness thus the molecules can undergo a splay (A, ) distortion. In a smectic film, any point distortion of the layer, e.g., arising from a surface feature, propagates for some distance into the film this feature is important for electrically addressed dynamic scattering devices. Bend ( 33) and twist ( 22) elastic constants approach infinity at the nematic (N) to smectic transition. 

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