Showing papers by "Samo Kralj published in 1998"
TL;DR: In this article, a modified induced-dipolem type coupling was used to simulate microscopic liquid crystal structures confined to a submicron cylindrical cavity and stability regions of characteristic nematic structures were determined as functions of the cylinder radius, homeotropic anchoring strength, and degree of the interaction anisotropy.
Abstract: Molecular dynamics is used to simulate nematic liquid crystal structures confined to a submicron cylindrical cavity. Molecules, fixed at the lattice points, are set to interact via a modified induced-dipole--induced-dipole type coupling. Stability regions of characteristic nematic structures are determined as functions of the cylinder radius, homeotropic anchoring strength, and degree of the interaction anisotropy. A connection linking elastic and microscopic approaches is established. Results confirm most of the predictions of the elastic free energy deep in the submicron regime.
38 citations
TL;DR: In this article, the phase behavior of pentylcyanobiphenyl (5CB) and octylcyane-binear (8CB) liquid crystals confined to controlled porous glass of different characteristic void sizes was studied using deuteron NMR.
Abstract: The phase behavior of pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB) liquid crystals confined to controlled porous glass of different characteristic void sizes $R$ is studied using deuteron NMR. In samples with the 5CB liquid crystal the discontinuous isotropic-nematic $(I\ensuremath{-}N)$ transition becomes gradual for $Rl0.025\ensuremath{\mu}\mathrm{m}.$ The discontinuous $I\ensuremath{-}N$ phase transition temperature shift $\ensuremath{\Delta}{T}_{\mathrm{IN}}$ scales as $\ensuremath{\Delta}{T}_{\mathrm{IN}}\ensuremath{\propto}{R}^{\ensuremath{-}1.3\ifmmode\pm\else\textpm\fi{}0.3}.$ A detailed theoretical analysis of the origins of the temperature shift and the change of the character of the $I\ensuremath{-}N$ and nematic--smectic-$A$ phase transition is given. The influence of the surface treatment is studied for the 8CB liquid crystal immersed in a $R=0.2\ensuremath{\mu}\mathrm{m}$ matrix. The results suggest that for the silane-treated sample the anchoring is homeotropic, whereas it is planar for the nontreated surface. In both cases the corresponding anchoring strength is estimated to be larger than ${10}^{\ensuremath{-}5}{\mathrm{J}/\mathrm{m}}^{2}.$ The smectic-$A$ ordering seems to be more affected by the confinement in the nontreated sample than the one treated by silane.
28 citations
TL;DR: In this paper, the influence of the inhomogeneous surface pretilt (slope) on chevron structures and on zig-zag defects in a SmC liquid-crystal cell is studied.
Abstract: The influence of the inhomogeneous surface pretilt (slope) on chevron structures and on zig-zag defects in a SmC liquid-crystal cell is studied. The experimentally observed effect of the confining substrate with controlled variation of the surface slope on the formation of zig-zag defects is qualitatively explained with the Landau–Ginzburg-type free-energy expanded in terms of the nematic director field and the smectic complex order parameter. Transitions in the C1 and C2 chevron structures are studied as functions of the surface pretilt angle θt. The threshold conditions are calculated. The width of the straight element of the domain wall (running parallel to the smectic layers) and the costs for its formation are estimated.
6 citations
TL;DR: In this paper, a deuteron NMR study of the 8CB liquid crystal confined to the controlled pore glass matrix is presented, and theoretical analysis based on the phenomenological Landau - de Gennes type description predicts a strong influence of the pore curvature on the confined 8CB smectic ordering, in good agreement with experiment.
Abstract: A deuteron NMR study of the 8CB liquid crystal confined to the controlled pore glass matrix is presented. The theoretical analysis based on the phenomenological Landau - de Gennes type description predicts a strong influence of the pore curvature on the confined 8CB smectic ordering and almost none on its nematic ordering, in good agreement with experiment.