On the Nature of Molecular Associations, Static Permittivity and Dielectric Relaxation in a Uniaxial Nematic Liquid Crystal

Abstract

One fluorinated terphenyl compound was studied by polarizing microscopy, x-ray diffraction and dielectric spectroscopy. It exhibits the nematic phase over a range of 107.8⁰. The average intermolecular distance was observed to be more than in systems without any lateral fluorine substitution. Apparent molecular length was found to be more than the molecular model length, suggesting presence of antiparallel molecular associations. Optimized geometry, obtained by molecular modeling, yielded a dipole moment of 6.68 D. The observed principal dielectric constants are consistent with respective components of dipole moments and show quite a high value of dielectric anisotropy. The threshold voltage and the splay elastic constant have also been determined. Flip-flop mode dielectric relaxation frequency is found to increase with temperature, and the activation energy for the process is found to be 35.53 kJ mol^–1.

Keywords:

• Activation energy
• dielectric and elastic constants
• dielectric anisotropy
• flip-flop relaxation mode
• molecular association
• terphenyl fluorinated nematic

Acknowledgment

The authors like to thank W. Haase, Institute of physical Chemistry, TU Darmstadt— Petersenstr. 20, Darmstadt, Germany for active help and support.