Effect of spontaneous polarization and polar surface anchoring on the director and layer structure in surface-stabilized ferroelectric liquid crystal cells.

Abstract

We use the Landau-de Gennes model to study theoretically the effect of the magnitude of the spontaneous polarization (P(S)), the ratio (r) between the equilibrium layer tilt and the smectic cone angle, the thickness of the insulating alignment layers and the strength of the polar and nonpolar surface anchoring on the director and layer structure in surface-stabilized ferroelectric liquid crystal cells with the chevron structure of smectic layers. The system shows a surprising number of stable structures, accompanied by one or two metastable ones. At P(S) greater than the critical value only quasimonostable structures, which can exhibit the thresholdless (V-shaped) switching, exist at all r and both at weak and strong polar surface anchoring. At lower P(S) bistable and monostable structures can coexist. Bistable structures can be expected at high r, low P(S) and if polar surface anchoring is weaker than the nonpolar one. Lowering the ratio r and/or increasing the strength of polar anchoring promotes the stability of monostable structures. Thicker insulating alignment layers also drive the system into the monostable state. Polar surface anchoring induces a large surface electroclinic effect. As a result the nematic deformations close to the surfaces are very strong and the stress is relieved by bending of the smectic layers. This leads to the formation of a double chevron structure which is stable at very large polar anchoring and due to the surface electroclinic effect it is metastable also at lower values of polar anchoring.