Optical Properties of Aligned Nematic Liquid Crystals in Electric Field

Abstract

In this study, the optical transmittance of aligned nematic liquid crystals (ANLCs) was investigated in terms of temperature variations through electrooptic effects under DC electric field. The optical transmittances of the planar and homeotropically aligned liquid crystal cells, which were prepared by conventional rubbing and photolithographic technique on the polyimide thin films for molecular alignment, were measured in their phase transition region. The results of measurement for both orientations, the distribution curve of the optical transmittance exhibits displacement toward to low level at the beginning and then to high level by the temperature variations, while the electric field increases. It was also observed that the domain structure of the materials were affected considerably by the applied electric field and phase transition region of the aligned structures had broader range than by the pure crystalline structure and its phase transition temperature was changed by the molecular anisotropy. Finally, in photolithographic method strong bonds between the molecules and the orienting surface were observed in high contrast to rubbing method.