The liquid-crystalline phase behaviour of hard spherocylinders with terminal point dipoles

Abstract

We examine the effect of dipolar interactions on the liquid-crystalline phase behaviour of L/D = 5 hard spherocylinders with a terminal point dipole. The hard spherocylinder consists of a cylinder of length L and diameter D with hemispherical caps on each end; the point dipole is located at the centre of the hemispherical cap (2.5D from the centre of the spherocylinder) and is oriented along the principal molecular axis. The phase transitions exhibited by this system are studied using the isothermal - isobaric Monte Carlo (MC-NPT) technique. As for systems with central dipoles, the terminal dipole is seen to slightly destabilize the nematic (orientationally ordered) phase relative to the isotropic phase when compared with the non-polar hard spherocylinders. More interestingly, the smectic (layered) phase is destabilized in the terminal dipole case, and is only seen at the very highest densities. This is in stark contrast to what is seen for systems with central point dipoles in which the smectic phase is stabilized relative to the nematic phase due to the strong anti-parallel dipolar interactions. We do not find any evidence for ferroelectric or anti-ferroelectric ordering in these systems.