Molecular Crystals and Liquid Crystals, Vol.515, 71-98, 2009
Influence of Hydrogen Bonding on Device Parameters and Field Response in N* and SmC* Phases of a Ferroelectric Liquid Crystal, HBFLC: 12 bpa
Isotropic to chiral nematic (IN*) and chiral nematic to chiral SmC(N*C*) transitions are studied by LF dielectric method in a hydrogen bonded ferroelectric liquid crystal, viz., 12bpa. They agree with TM and DSC reports. Tilt angle, electro-clinic effect, spontaneous polarization, and dielectric relaxations are investigated and compared with that of an odd homologue 11bpa. Growth of tilt and spontaneous polarization as order parameters in SmC* phase agree with mean-field prediction. Effect of H-bonding on the growth of tilt and PS order parameters is discussed. Observed large EC-effect is explained by the inclined configuration of soft-covalent interaction. Dielectric dispersion revealed a collective response, viz., Goldstone mode at 100Hz in SmC* and an LF-mode in N* phases. The two HF-relaxations, i.e., Types I and II in N* and SmC* phases are explained through a refined dipole model. Shift of GM with field in SmC* is explained. Off-centred dispersion is explained through the Cole-Davidson relation. HF relaxations are related to the individual dipole reorientation. Shift of fR with T infers higher activation energy for Type I and lower activation energy for Type II relaxations. Soft mode permittivity follows the Curie-Weiss law in the vicinity of TN*C*. Device parameters, viz., thermal stability, tilt angle, and spontaneous polarization in SmC* phase are found to be influenced by H-bonding in FLCs. Results are is discussed and compared with the data reported on 11bpa and other FE materials.