Transient and steady electric currents through a liquid crystal cell

Abstract

This paper presents a study of the transient and steady electric currents through a pentyl-cyano-biphenyl (5CB) nematic liquid crystal (LC) cell. It is demonstrated that space-charge effects are important, contrary to what has been observed before. Specifically, the nematic interlayer can be considered as an inhomogeneous medium, with near-electrode double layers emerging due to adsorption of ions present in the LC. The bulk of the LC contains charge carriers of both signs, which might be either extrinsic (impurity-induced) or intrinsic. In the latter case, they could consist of heavy fragments of LC molecules or anion and cation radicals, induced by redox processes near the electrodes. In the steady-current regime, the current–voltage characteristics are, most probably, governed by a space charge distributed in the nematic. For large enough biases U, the steady current approaches the Ohmic regime due to the depletion of the space-charge cloud. The observed transient-current phenomena suggest at least two types of charge carriers.

Keywords:

• 5CB
• dc conductivity
• space charge

Acknowledgements

The authors are grateful to Lyudmila Bugaeva and Alexander Kovalchuk for helpful discussions. AMG and AIV are grateful to Kasa im. Józefa Mianowskiego, Polski Koncern Naftowy ORLEN, and Fundacja Zygmunta Zaleskiego as well as to Project N 23 of the 2009–2011 Scientific Cooperation Agreement between Poland and Ukraine for the financial support of their visits to Warsaw. AMG is grateful to the 2009 and 2010 Visitors Programs of the Max Planck Institute for the Physics of Complex Systems (Dresden, Germany) for the support of his study.