Stability of the nematic phase of dimerizing aligned cylinders with respect to the smectic and columnar phases

Abstract

The limit of stability of the nematic phase for dimerizing parallel cylinders is examined. The dimers consist of two cylinders bonded end-to-end to form a rigid cylinder. A bifurcation analysis following Mulder is undertaken and the bifurcation point for instability with respect to a smectic A phase is shown to be postponed to higher densities. It is shown that the formation of dimers disrupts the smectic layering. Columnar ordering is also studied and found to be affected little by end-to-end dimers. The phase behaviour of the dimerizing fluid is found to be strongly temperature dependent, and a reentrant nematic phase is observed for a small range of pressures. For these pressures the theory predicts nematic to smectic A to nematic to columnar phase transitions with decreasing temperature at constant pressure. To our knowledge this is the first time a reentrant liquid crystalline phase has been predicted for a microscopic model of a mesogenic molecule. The behaviour at the molecular level is examined for the nematic-smectic A instability and the possibility of two smectic A phases being present is discussed.