We model order parameter changes in confined nematic liquid crystals using the Q-tensor theory developed by de Gennes and based upon Landau's theory of superconductors. This theory, although only valid close to the nematic to isotropic phase transition, has proved to be useful in modelling areas of high distortion, near defects and close to surfaces.
Q-tensor modelling has been of recent interest due to the development of display devices which utilise defect structures and defect motion during switching. These bistable devices may be switched using a flexoelectric coupling or flow effects.
We have been modelling both the Zenithal Bistable Device (ZBD, see figure below) and the Post-Aligned Bistable Nematic (PABN) which both include defect structures.
Figure: The defect state of the ZBD device modelled using Q-tensor theory
This work is undertaking in collaboration with Hewlett-Packard Labs, Bristol.
Reference:
N. J. Mottram and C. Newton, Introduction to Q-tensor theory, University of Strathclyde, Department of Mathematics research report, 2004:10 (2004). [pdf]