Phenomenological theory of the direct isotropic to hexatic-B phase transition.

Monte Carlo simulation studies have demonstrated the possibility of the first order isotropic to smectic-B phase transition. We present a mean-field description of the direct isotropic to hexatic-B phase transition. We analyze the question under which conditions a direct isotropic to hexatic-B phase transition is possible when compared to other phase transitions. Within this model the direct isotropic to hexatic-B phase transition is found to be always strongly first order than the isotropic to nematic and isotropic to smectic-A phase transitions. The presented analysis is in good agreement with Monte Carlo simulation studies.