Effect of Core and Its Position on the Properties of Fluorinated Nematic Liquid Crystals

Abstract

Five nematic liquid crystal (NLC) compounds have been investigated by polarizing optical microscopy (POM), molecular mechanics and dielectric spectroscopy. Introduction of ethane (– CH2CH2–) bridge, its position, surrounding rings and fluorination were found to influence considerably molecular dipole moment (μ), inclination (β) i.e., frame of reference, dielectric anisotropy (Δε), threshold voltage (Vth), splay elastic constant (K11), relaxation time (τ ) and activation energy (Ea). It is observed that compounds show very lower melting and clearing temperatures. Nematic (N) phase stability is also found to be broader. All compounds show super cooling property near to room temperature except compound 3o2pp-f (N1). Splay elastic constant (K11), an important parameter is found to vary from 10−11 N to 10−10 N. Comparatively lower value of K11, lower value of restoring torque and alternatively faster response can be achieved. Undesirable energy absorption is found in between few hundred kHz to MHz region i.e flip-flop in nature.