THE LIQUID-CRYSTALLINE PHASE-BEHAVIOR OF HARD SPHEROCYLINDERS WITH TERMINAL POINT DIPOLES

We examine the effect of dipolar interactions on the liquid-crystallin e phase behaviour of L/D = 5 hard spherocylinders with a terminal poin t dipole. The hard spherocylinder consists of a cylinder of length L a nd 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 a xis. 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 destabi lize the nematic (orientationally ordered) phase relative to the isotr opic phase when compared with the non-polar hard spherocylinders. More interestingly, the smectic (layered) phase is destabilized in the ter minal dipole case. and is only seen at the very highest densities. Thi s is in stark contrast to what is seen for systems with central point dipoles in which the smectic phase is stabilized relative to the nemat ic phase due to the strong anti-parallel dipolar interactions. We do n ot find any evidence for ferroelectric or anti-ferroelectric ordering in these systems.