Showing papers by "Samo Kralj published in 1995"

Saddle-splay elasticity of nematic structures confined to a cylindrical capillary

Abstract: The stability of nematic structures within a cylindrical capillary whose wall exhibits a homeotropic boundary condition is studied. The structures are obtained numerically from Euler-Lagrange equations resulting from the minimization of the Frank free energy functional. Stability diagrams are presented showing dependence on elastic properties, surface anchoring, and external transversal field strength. Emphasis is given to the effects of the saddle-splay elastic constant (${\mathit{K}}_{24}$), which plays an important role in the weak anchoring regime. A new structure---the planar polar structure with two line defects---is predicted. It is shown that it is stable in a finite interval of the external field strength in the strong anchoring regime.

Deuteron NMR study of liquid crystals confined in aerogel matrices

Abstract: The temperature dependence of the deuteron NMR line shape was studied in pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB) liquid crystals confined in porous silica aerogel matrices with two different pore size distributions. The average pore sizes 〈${\mathit{R}}_{\mathit{c}}$〉 of the two aerogel matrices were 0.8 and 0.2 \ensuremath{\mu}m, respectively. The deuteron NMR lines of 5CB and 8CB confined liquid crystals are in the isotropic regime broader than in the corresponding bulk phases. This observation shows that the interaction with the aerogel internal surface induces nematic order far above the bulk isotropic-nematic transition temperature. The nematic-isotropic (N-I) transition for both confined liquid crystals is continuous. No hysteresis was observed. A simple Landau-type model is used to describe these observations.

Landau-de Gennes theory of the core structure of a screw dislocation in smectic A liquid crystals

Abstract: We present details of calculations of the core structure of a screw dislocation in a smectic A liquid crystal, using the phenomenological Landau-de Gennes free energy functional. The order parameter frustration created by topological constraints far from the dislocation core is resolved in one of three qualitatively different ways. The three types of dislocation core solution are the DT (double twist), CL (classical), and BP (broken polar symmetry) solutions, respectively. The stability requirements for these structures are discussed, as a function of temperature, smectic elastic properties, and coupling between smectic and nematic order. The effect of possible inhomogeneity between left- and right-handed conformers is also examined.