Title: Theories of the Smectic Liquid Crystal State

Abstract: Smectic liquid crystals, first identified merely as "slimy
liquid crystals" by Otto Lehmann in the late 1880s, were finally
identified as layeredphases by Georges Friedel in 1922. There are two
principal phases, the smectic A phase (in which molecules are oriented
normal to layers), and the smectic C phase (in which they aren't). In
this talk shallintroduce the subject by discussing standard theories
of this state at the mean-field and Landau level. One feature of
particular interest is the nature of the transition between the
orientationally ordered nematic phase and the smectic phase. I shall
illustrate some important issues by using examples from my own work,
some of which are more successful than others. I shall conclude by
discussing recent work in collaboration with Osipov and coworkers
concerning the so-called de Vries phases, in which the thickness of
the layers is relatively temperature independent.