Microscopic Aspects of the Smectic Phases
First the empirical information on the molecular factors that influence smectic behaviours will be summarized. The various types of molecular model and commonly accepted concept that are supposed to lead to smectic layering will be evaluated. Introduction of a coupling between the smectic order parameter and any other relevant order parameter can drive the nematic-smectic A phase transition from second order to first order. Next the breaking of up-down symmetry will be considered, which can have either a steric or a polar origin. The presence of strong terminal permanent dipoles leads to various types of smectic A phase. The role of dipolar interactions will be discussed in some detail, including its importance for the occurrence of reentrant nematic behaviour. However, the latter effect is not restricted to strongly polar systems. Finally the origin of tilted smectic phases will be discussed.
KeywordsDipole Moment Dielectric Permittivity Nematic Phase Orientational Order Tricritical Point
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