Dielectric Properties in the Nematic and Isotropic Phases of Di-n-Propyloxyazoxybenzene (3.OAOB) and Di-n-Pentyloxyazoxybenzene (5.OAOB)

Abstract

Results of dielectric relaxation studies of two members of 4, 4′-n-alkoxyazoxybenzene homologous series, 3.OAOB and 5.OAOB, are presented. On the basis of dielectric spectra obtained for parallel (ε_∥*) and perpendicular (ε_⊥*) orientations of the samples with respect to measuring electric field the following problems are discussed: (i) the sign change of dielectric anisotropy when frequency increases from radio to microwave range; (ii) influence of the local field factor on the dipole correlation time in the nematic phase, and (iii) mechanism of molecular reorientations taking into consideration the dielectric spectra of three substances having different electric structures. It was concluded that the main molecular process contributing to the high frequency dielectric spectra of the nematic phases is the reorientation around the long axis of molecule as a whole, characterized by the relaxation time τ_⊥ ^DR ≅ 85 ps, whereas the QNS method reflects the internal reorientations of two molecular moieties around N—phenyl bonds with the correlation times τ^QNS = (4 ÷ 9) ps.

Key Words:

• di-n-propyloxyazoxybenzene
• di-n-pentyloxyazoxybenzene
• dielectric anisotropy
• dielectric relaxation
• nematic
• molecular motion