Hexatic ordering in liquid crystal films

For many decades, the lamellar liquid crystal phases with the general label ‘smectic’ were considered to be quite mysterious. However, developments in theories of melting in two dimensions have led to the introduction of the concept of fluids with bond orientational (hexatic) order. Application of these concepts to liquid crystals leads to a natural Classification of the smectic phases. Simultaneous with these theoretical developments, synchrotron X-ray studies of free-standing liquid crystal films have provided new, incisive experimental information in two and three dimensions which has confirmed the basic model. This in turn has led, through concepts adopted from renormalization group theories of multicritical phenomena in magnets, to a detailed model for the growth of two-dimensional and three-dimensional smectic liquid crystals having bond orientational order.