Introduction to Liquid Crystalline Phases
This chapter deals principally with structural aspects of liquid crystalline phases – the necessary asymmetry of the molecular structure, the way in which molecules assemble into layers or columns, and the larger-scale structures visible in the optical microscope.
There is a discussion of the molecular asymmetry which makes liquid crystalline behaviour possible, and then the structures of nematic, smectic and columnar phases are described. The hierarchy of smectic structures is outlined, together with the corresponding scheme for columnar structures.
Un-aligned samples of liquid crystalline phases spontaneously adopt characteristic ‘textures’ which have relaxed down to their lowest accessible energy state. For nematic phases these tend to have linear ‘disclinations’ and for smectic phases, the layers curve into ‘focal conic’ structures. The geometry of these structures is apparent when they are viewed with polarized light in an optical microscope, and the principal ‘optical textures’ of liquid crystal are explained.
The final section concerns X-ray diffraction patterns. As the crystalline solid is heated and passes through a succession of phases, the loss of order causes a stepwise change in the appearance of the diffraction pattern. Sharp features in the diffraction pattern of the crystalline solid, broaden and then disappear, one by one, until only very diffuse features remain for the isotropic liquid.
KeywordsLiquid Crystal Nematic Phase Liquid Crystalline Phasis Liquid Crystal Phasis Molecular Alignment
I acknowledge with gratitude, the extensive advice and help which I have received from Professor Richard Bushby whilst preparing this chapter. I am also grateful to Professor John Goodby for his advice concerning the section on smectic phases and to Professor Rob Richardson and Professor A. C. T. North for advice on X-ray diffraction patterns of mesophases.
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