Multicriticality in smectic liquid crystals

A phenomenological model permitting a unified description of different types of smectic liquid crystalline phases including the hexatic-B phase has been developed. The model describes five different liquid crystalline phases: nematic (N), smectic-A (SmA), smectic-C (SmC), hexatic-B (HexB) and smectic-E (SmE). We observe various multicritical points among different smectic phases. General arguments are presented for the topologies of the phase diagrams in the vicinity of the SmA–SmC–HexB and N–SmA–SmC bicritical points and in the vicinity of the SmA–HexB–SmE, SmA–SmC–SmE and SmC–HexB–SmE triple points. The existence of the SmA–HexB, SmA–SmC and SmC–HexB tricritical points near the SmA–HexB–SmE, SmA–SmC–SmE and SmC–HexB–SmE triple points is discussed. Calculations based on this model agree qualitatively with the experiments.