The structure of chiral Sm C* liquid crystals in planar samples and its change in an electric field

Abstract

From observation by microscope of DOBAMBC and mixtures of smectic C and cholesteric, a structure of SmC* in planar samples has been determined as depending on the sample thickness d. In all samples there are unwound layers at the sample surfaces with dipole-moments directed from the surface to the sample bulk. In thick samples the regular helicoidal structure occurring in the sample bulk is connected to the unwound surface layers by means of ±2π disinclination lines, the upper and lower lines being shifted by half a helical step p. In thin samples (d≃p) the helical structure is unwound by surface anchoring but there is a twist along the sample thickness. The unwinding process of thick samples in electric field proceeds in two steps: unwinding of the helix via mutual annihilation of opposite disinclinations at critical field E c1 and removal of the twist at E c2 . With thin samples only unwinding of the twist at E c2 takes place Determination de la structure de la phase lamellaire SmC* en geometrie planaire pour differentes epaisseurs de l'echantillon par observation au microscope polarisant d'un compose chiral (DOBAMBC) et de melanges de SmC et de cholesterique