Gradient flexoelectric switching response in a nematic phenyl benzoate

Abstract

We report on the inverse flexoelectric effects observed in a nematic liquid crystal with a small positive dielectric anisotropy subject to static and very low frequency (<1 Hz) a.c. fields. The Bobylev–Pikin flexobands appear at a temperature‐dependent d.c. threshold. Under square wave excitation, a new type of transient optical response occurs soon after each polarity reversal, and we ascribe it to the gradient flexoelectric distortion explicable on the basis of the presence of intrinsic double layers. This instability is characterized by a threshold voltage that decreases with temperature. Its maximum amplitude increases linearly with voltage close to threshold, and occurs after polarity reversal at a time τ_m that scales inversely as the voltage; τ_m decreases exponentially with frequency and temperature. After each polarity change, the ionic current following the charging current decreases almost exponentially to a non‐zero value; the residual current increases monotonically with the applied bias.

Acknowledgments

We are grateful to Dr S. Krishna Prasad (Centre for Liquid Crystal Research, Bangalore) and Professor N. V. Madhusudana (Raman Research Institute, Bangalore) for their keen interest in this investigation. We are indebted to M/s Eastman Organic Chemicals for supplying, free of charge, the sample of BEPC used in this study.