Classical Smectic A Phase

The classical SmA phase can form on cooling the nematic phase or directly from the isotropic phase. Now we meet a new feature the phase becomes periodic in one direction. In Fig. 4.6 the interlayer distance equal in this case to period is marked by letter d. Thus, the SmA phase is simultaneously a one-dimensional solid and a two-dimensional liquid. There is no correlation between molecular positirms in the neighbor layers. Such a phase predominantly forms by more or less symmetric molecules with long alkyl chains. 

The value of pi is usually taken as translational order parameter, see Section 6.3. 

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