Columnar phases of achiral vanadyl liquid crystalline complexes

Two liquid crystalline vanadyl complexes have been studied by frequency dom ain dielectric spectroscopy over the range 10 mHz to 13 MHz. The materials exhibit two or three columnar phases denoted Col(ro), Col(rd), and Col(hd) that were identified by X-ray diffraction. In the higher temperature Col(ro ) phase, a relaxation process in the kHz range is observed that is attribut ed to the reorientation about the molecular short axis. A pronounced dielec tric relaxation process shows up in the low temperature Col(ro) phase at he rtz and sub-hertz frequencies. This slow relaxation is assigned to reorient ation of the molecular dipoles within the polar linear chains, which are al igned along the column's axis. Triangular wave switching studies at low fre quency reveal processes inside the Col(ro) phase which are most probably du e to ionic/charges relaxations but a ferroelectric switching for an achiral discotic system cannot be ruled out completely. Below the Col(ro) phase th ere is an orientationally disordered crystalline Cr-x phase with disordered side chain dipoles. A dielectric relaxation process connected with the int ramolecular relaxation of the alkoxy side chains, similar to the beta-proce ss of polymers, has been found in the lower temperature Cr-x phase.