Optical Determination of Twist Elastic Constant of the Chiral Smectic Liquid Crystal SCE8

Abstract

When a “thick” device is filled with a chiral smectic liquid crystal material, a helix is allowed to evolve within the device. In this paper, such a device was fabricated and filled with the ferroelectric liquid crystal material, SCE8. Application of voltage to the device will cause a deformation of the helix, and hence a deviation of the optic axis. The optical response of the device due to the applied voltage, was obtained experimentally. The helical deformation was also theoretically modeled using the continuum approach. In this paper, two different theoretical models will be presented. The first model is a one dimensional model which calculates the director variation along the helical axis. The second model is a two dimensional model which calculates the director variation through the thickness of the device, and along the helical axis. Comparison of the theoretical and experimental results allows us to calculate the twist elastic constant, B ₃ . The values of B ₃ for SCE8 obtained using the two different models will be discussed.

Keywords:

• Ferroelectric
• helix deformation
• twist elastic constant

Acknowledgments

SMS would like to thank the University of Malaya for sponsoring her attendance at FLC03. LPJ would like to thank the Royal Society for financial support.