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

• Published in: Liquid crystals Vol. 43; no. 10; pp. 1462 - 1471
• Main Authors: Etxebarria, J., Rodríguez-Conde, S., Ortega, J., Sanz-Enguita, G., Folcia, C. L.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 08.08.2016; Taylor & Francis Ltd
• Subjects: AC electric fields; crystal rotation method; Crystals; Electric fields; flexoelectricity; twisted nematic cell
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2016.1181215

We show that the crystal rotation method for measuring the difference between splay and bend flexoelectric coefficients (e 1 -e 3 ) [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 (e 1 -e 3 ) is obtained from a scale factor in a one-parameter fit. Measurements of the temperature dependence of (e 1 -e 3 ) are presented for two classical nematic materials.