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Showing papers by "Samo Kralj published in 1999"


Journal ArticleDOI
TL;DR: The core of a line defect with topological charge M=1 is uniaxial in the axial direction and it seems that the core of the point defect does not depend on the far nematic director field in the bulk limit.
Abstract: We study the biaxial structure of both line and point defects in a nematic liquid crystal confined within a capillary tube whose lateral boundary enforces homeotropic anchoring. According to Landau--de Gennes theory the local order in the material is described by a second-order tensor $\mathbf{Q},$ which encompasses both uniaxial and biaxial states. Our study is both analytical and numerical. We show that the core of a line defect with topological charge $M=1$ is uniaxial in the axial direction. At the lateral boundary, the uniaxial ordering along the radial direction is reached in two qualitatively different ways, depending on the sign of the order parameter on the axis. The point defects with charge $M=\ifmmode\pm\else\textpm\fi{}1$ exhibit a uniaxial ring in the plane orthogonal to the cylinder axis. This ring is in turn surrounded by a torus on which the degree of biaxiality attains its maximum. The typical lengths that characterize the structure of these defects depend both on the cylinder radius and the biaxial correlation length. It seems that the core of the point defect does not depend on the far nematic director field in the bulk limit.

108 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of confined geometry on the smectic A-smectic C* phase transition in the ferroelectric liquid crystal CE8 has been analyzed using an electro-optic response technique, the temperature dependence of elementary excitations in thin, homogeneously aligned, wedgetype cells of thickness from 0.25 to 4mum has been measured for different thicknesses of the aligning layer.
Abstract: The influence of confined geometry on the smectic A-smectic C* phase transition in the ferroelectric liquid crystal CE8 has been analysed. Using an electro-optic response technique, the temperature dependence of elementary excitations in thin, homogeneously aligned, wedgetype cells of thickness from 0.25 to 4mum has been measured for different thicknesses of the aligning layer. In the case of a thin aligning layer (15nm), we observe in the smectic C* phase an increase of the relaxation rate of the phase excitations and a decrease of the phase transition temperature, both of which are proportional to the inverse of the cell thickness. For a thick aligning layer (50 nm), the relaxation frequency and the transition temperature are proportional to the inverse square of the cell thickness. This indicates that the surface anchoring energy depends on the thickness of the aligning layer. For CE8 on nylon, we obtain a surface anchoring energy W=10-4 Jm-2 for a thin aligning layer, and strong anchoring with W>5x10-...

11 citations