Improvement of the crystal rotation method to measure the flexoelectric difference (e₁–e₃) in achiral materials using AC electric fields

ABSTRACT

We show that the crystal rotation method for measuring the difference between splay and bend flexoelectric coefficients (e₁–e₃) [Outram and Elston, Liq. Cryst. 39, 149 (2012)] can be improved by using AC instead of DC fields. The field frequency is small (~0.05 Hz), yet sufficient to get rid of the difficulties connected with the migration of charge carriers. The method is sensitive enough so as to use fields with amplitudes as small as 1 V/mm. This has the advantage of avoiding the consideration of the interaction due to the dielectric anisotropy, and greatly simplifies the analysis of data. The results are extracted from a simple fitting scheme, which involves two parameters. In particular (e₁–e₃) is obtained from a scale factor in a one-parameter fit. Measurements of the temperature dependence of (e₁–e₃) are presented for two classical nematic materials.

Graphical Abstract

KEYWORDS:

• flexoelectricity
• crystal rotation method
• twisted nematic cell
• AC electric fields

Acknowledgements

This work is supported by the Basque Government (Project IT 1130-16). S. R-C and G. S-E thank the UPV/EHU for a grant.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by the Basque Government: [Project IT 1130-16].