Soliton dynamics of geometrically confined ferroelectric liquid crystals

Abstract

We show that geometrical confinement of Sm C* type ferroelectric liquid crystals between two parallel boundaries separated by a distance d induces a soliton structure similar to the one obtained in a transverse external magnetic field. For non-polar surface anchoring (i.e., quadrupolar boundary conditions) the (T, d) phase diagram in fact closely resembles the (T, H) phase diagram and the unwinding of the smectic C* helix is preceded by a transition from the plane-wave to the soliton like helical structure. The periodic potential of the soliton lattice induces a gap in the phason dispersion relation similar to the gaps between the valence and conduction bonds of an electron in a periodic potential. For a system with polar boundary conditions the splay distortion of the director field is accompenied by a splayed polarization and a soliton like deformation of the phase profile across the cell. A transverse solitary wave excitation with a (l/d ²) relaxation rate thickness dependence and a finite frequency gap at l/d ² = 0 has been observed at small thicknesses. A cross-over to a gapless plane-wave like dynamics has been found at large thicknesses.

Key Words:

• Liquid crystals
• solitons