Dynamics of the molecular orientation field coupled to ions in two-dimensional ferroelectric liquid crystals

TL;DR

This paper develops a theory describing how slow-moving ions influence the dynamics of molecular orientation in two-dimensional ferroelectric liquid crystals, highlighting an overlooked ionic contribution in light scattering experiments.

Contribution

It introduces a coupled dynamics model of molecular orientation and ionic charge, emphasizing the ionic effects on light scattering measurements in ferroelectric liquid crystals.

Findings

Ionic configuration significantly affects scattered light intensity.

Theoretical model shows the importance of ionic effects in orientational fluctuation dynamics.

Previous models may have overlooked critical ionic contributions.

Abstract

Molecular orientation fluctuations in ferroelectric smectic liquid crystals produce space charges, due to the divergence of the spontaneous polarization. These space charges interact with mobile ions, so that one must consider the coupled dynamics of the orientation and ionic degrees of freedom. Previous theory and light scattering experiments on thin free-standing films of ferroelectric liquid crystals have not included this coupling, possibly invalidating their quantitative conclusions. We consider the most important case of very slow ionic dynamics, compared to rapid orientational fluctuations, and focus on the use of a short electric field pulse to quench orientational fluctuations. We find that the resulting change in scattered light intensity must include a term due to the quasistatic ionic configuration, which has previously been ignored. In addition to developing the general theory, we present a simple model to demonstrate the role of this added term.