Deformation of the Helical Structure during the Unwinding and Winding Process of Ferroelectric Liquid Crystals

Abstract

The effect of magnetic field on the molecular alignment of ferroelectric liquid crystals is observed on the cooling process from an isotropic phase to a chiral smectic C phase. In a sample having phase sequences I-N*-SA-SC *, the monodomain is formed under the magnetic field. The texture change relating to the deformation of the helical structure is investigated in the monodomain. When a d.c. voltage is applied in the SC * phase, the focal conics appear at a low voltage range below the threshold for unwinding of the helix. While the voltage is decreased after the unwinding, the helical structure begins to form from the focal conics. The electrooptic effect induced by the deformation of the helical structure depends on the molecular alignment in the SC * phase.

Non-linear behaviour of phason mode with bias field in ferroelectric liquid crystals

“…The switching in the DHFLC material is due to the combination of bulk and surface effects meaning that the viscosity plays an important role in the switching phenomenon of DHFLCs. In contrast, switching in FLCs is mainly due to surface effects [23] and hence the viscosity does not play a major role in the switching phenomenon of FLCs [24]. When we apply the dc bias field parallel to the smectic layers, a deformation in the helical structure occurs due to the alignment of the polarisation vector in the field direction.…”

“…When we apply the dc bias field parallel to the smectic layers, a deformation in the helical structure occurs due to the alignment of the polarisation vector in the field direction. The molecules at the surfaces of the substrate may be more sensitive to the field in comparison to those wound in the bulk and they tend to align parallel to the surfaces [24]. On further increasing the bias, the molecular orientation in the bulk switches to add its contribution to the molecular orientation-reorientation process.…”