Control and evaluation of liquid crystal molecules using ultrasound vibration

Nematic liquid crystals are widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. The authors have proposed a technique to control the orientation of liquid crystal molecules using ultrasound vibration without indium tin oxide electrodes. An ultrasound liquid crystal cell was fabricated; it consists of a liquid crystal layer sandwiched by two glass plates having two ultrasound PZT transducers. When exciting the transducers at the resonance frequencies, the flexural vibration modes were generated on the cell and the acoustic radiation force acted to the liquid crystal molecules so that the orientation direction can be changed. The relationship between the molecular orientation and the vibration distribution of the cell was investigated from the transmitted light distribution of the liquid crystal cell under the crossed Nicol condition. In addition, the orientation of liquid crystal molecules was evaluated as ultrasonic wave velocity in the GHz range by the Brillouin scattering method. The ultrasonic wave velocity in the long axis direction of the liquid crystal molecules was higher than that in the short axis direction, which indicates the uniaxial anisotropy of the liquid crystal molecules.