A magneto and electrooptic study of ferroelectric liquid crystals
The interactions between external fields and liquid crystals and lipid tubules are discussed, with emphasis on ferroelectric liquid crystals. The electric field alignment of phospholipid tubules along the field direction was achieved at a relatively small field, where a light scattering technique was employed to deduce an effective dielectric anisotropy. A macroscopic mechanism was introduced based on depolarization to explain the large anisotropy, which is totally different from the inherent anisotropy. Theoretical calculations based on this mechanism agree with the light scattering data. Turning to liquid crystals, crossed magnetic and electric fields were applied to the chiral liquid crystal DOBAMBC in the Smectic A phase in such a way as to maintain the director normal to the smectic layers. Near the smectic C* transition it was found that E propto H^2 and that dE/dH^2, the "magnetoelectroclinic coefficient", versus temperature exhibits behavior consistent with a temperature-dependent polarization-tilt coupling coefficient. This result offers an explanation for the anomalous electroclinic susceptibility exponent ? = 1.11 observed by Garoff and Meyer. A tilt ? of the principal axis of the optical dielectric tensor linear in a transverse electric field was observed in the nemat ic phase for the ferroelectric liquid crystal SCE12 in a surface-stabilized sample. The electroclinic coefficient d?/dE was observed to increase rapidly on approaching the NA transition from above. This indicates that translational order is important to the magnitude of this effect, even though not essential to the existence of this effect. A simple symmetry based theory involving coupled order parameters is presented. Critical behavior is investigated for this effect and different experimental tools were utilized to probe this effect. The dynamics of the electroclinic effect was studied, and an anomaly in this effect was found below the NA phase transition. The apparent response time of this effect is not monotonically decreasing on approaching the NA transition from below as is the amplitude of this effect. Dielectric measurements were performed and the results are indicative of a possible high frequency mode in addition to the electroclinic soft-mode.
School:Case Western Reserve University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:magneto electrooptic ferroelectric liquid crystals
Date of Publication:01/01/1991