Evaluation of Molecule Orientation on Liquid Surface in Transient State Using by Anisotropic Reflection

Abstract

A technique to evaluate transiently the orientation director of liquid crystal on the surface of thin liquid film using by measuring the anisotropic reflection of S-polar and P-polar at incidence angle which is near Brewster's angle is developed. The high-speed rotary half-wave plate type polarized state generator, which rotates the light polarized direction with a constant speed, is applied on the prove light. The modulated laser beam is irradiated on the surface at a certain incident angle, and the light intensity of the reflection beam is measured. The maximum and minimum values of each period of the measured light intensity shows the reflected light intensity of the S- and P-polarized light, respectively. The Brewster's angle of orientation film depends on azimuth angle between the orientation direction and the plane of incidence, because Brewster's angle is decided by the refractive index and these films have the birefringence. The phase changing process from the nematic to the cholesteric phase on the coating film of a Hydroxypropylcellulose 50 wt% aqueous solution during drying was evaluated by measuring dependence of Brewster's angle on the azimuth angle. The result shows a good agreement with the birefringence and dichroism evaluated by the transmitted light.