Experimental Investigation on Pretilt Angle in Binary Liquid Crystal Composed of Highly Polar Molecules

Abstract

We report the measurement of dielectric constants, birefringence, and pretilt angle in binary mixtures of nematic liquid crystals (CP7B and CCN-47). CP7B has a strong longitudinal dipole moment and exhibits a large positive dielectric anisotropy (Δε=ε_|| -ε_⊥>0) and CCN-47 has a strong transverse dipole moment and exhibits a large negative dielectric anisotropy. In the mixtures, ε_|| increases with increasing CP7B concentration, whereas ε_⊥ remains almost constant. We show that the pretilt angle increases with Δε and birefringence (Δn=n_e-n_o) much rapidly than reported earlier. It is suggested that this effect may arise due the presence of strong permanent dipole moments in the molecules.