Electro-optical switching properties for measuring the parameters of a ferroelectric liquid crystal

• Published in: Liquid crystals 2005-03, Vol.32 (3), p.307-314
• Main Authors: Essid, S., Manai, M., Gharbi, A., Marcerou, J. P., Rouillon, J. C.
• Format: Article
• Language: English
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678290500033596

We present a description of the reorientation of the macroscopic polarization P S under a switching field in a ferroelectric liquid crystal assuming the direction of P S is spatially uniform but time-dependent throughout the sample. The driving torques are then the linear ferroelectric coupling and the quadratic dielectric torques. If the theory is correct, some of the important parameters of a FLC may be determined in a single experiment, such as the spontaneous polarization P S , the switching delay t m , the switching time τ, the orientational viscosity η and the dielectric anisotropy ε a . The measurements are performed using new compound, as a function of temperature with different field strengths and sample thicknesses. The experiment appears to be poorly fit by the so-called 'rigid' hypothesis leading to the conclusion that the switching of polarization is not uniform but rather starts locally from orientational defects and propagates quickly throughout the sample. This reinforces the view that the driving torque equation is nothing but the Sine-Gordon equation reminiscent of soliton propagation.