Mesogen polarity effects on biaxial nematics. Centrally located dipoles.

We investigate the phase organisation of thermotropic biaxial Gay-Berne (GB) mesogens yielding a biaxial nematic (Nb) phase upon endowing them with a central point dipole. We study the effects of changing the strength and orientation of the dipole on the phase behaviour, and in particular we examine, using molecular dynamics (MD) simulations, the possibility of improving the stability of the Nb phase. After mapping the boundaries of the Nb phase, we find that the strength of the embedded dipole is the parameter with the strongest influence on the mesogenic properties, while its orientation plays a minor role. For these central dipole systems, we find that the Nb phase organisation is stable only for mesogens with relatively weak dipole moments, while it disappears if electrostatic interactions become comparable in magnitude with dispersion interactions.