Travelling polarization walls in freely suspended smectic C* films

Abstract

We present electro-optical experiments in ferroelectric freely suspended smectic films using reflective polarizing microscopy. The observation of travelling 180° walls (kinks) in the film plane is described. The c-director alignment at the lateral film boundaries initiates the kink formation when the polarity of an external in-plane electric field is reversed. We analyze quantitatively the electric field dependence of the kink profiles, their widths and propagation speeds. A model for the kink formation and propagation is given. In addition to the conventional terms for viscous, elastic and electric torques it allows for the interaction of the spontaneous polarization with the electric field caused by polarization charges in the wall.

Keywords:

• Smectic films
• Ferroelectric switching
• Electro-optic effects
• Kink propagation