Gravitational field-induced orientational transition of aligned nematic liquid crystals

Abstract

We demonstrate induced orientational transition of liquid crystal (LC) E7 between two optical fibre tips in a gravitational field as a result of minimising the free energy. The LC orientational transition is from a homeotropic state, with respect to fibre tip, to a tilted state as the spacing between two fibre tips is increased. The orientational distortion introduces birefringence in the optical fibre that changes the polarised direction of the output light. At short spacing, the undistorted homeotropic orientation of LC is preferred. However, at longer spacing, a distorted orientation is preferred. Once the LC director profile is known, a Finite Difference Time Domain method is used to calculate the optical properties, which agree well with the experimental results.

Keywords:

• liquid crystals
• orientational transition
• birefringence
• FDTD

Acknowledgements

This work was supported by the NASA EPSCOR program under grant number NNX07AT55A, and NSF EPSCOR program under grant number SUB-2008-EPS-0814103-CIDEN-UAH.