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Chemical Physics Publications

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Full-Text Articles in Physics

Undulations Of Lamellar Liquid Crystals In Cells With Finite Surface Anchoring Near And Well Above The Threshold, B. I. Senyuk, Ivan I. Smalyukh, Oleg Lavrentovich Jul 2006

Undulations Of Lamellar Liquid Crystals In Cells With Finite Surface Anchoring Near And Well Above The Threshold, B. I. Senyuk, Ivan I. Smalyukh, Oleg Lavrentovich

Chemical Physics Publications

We study the undulations instability, also known as the Helfrich-Hurault or layers buckling effect, in a cholesteric liquid crystal confined between two parallel plates and caused by an electric field applied along the normal to layers. The cholesteric pitch is much smaller than the cell thickness but sufficiently large for optical study. The three-dimensional patterns of the undulating layers in the bulk and at the surfaces of the cells are determined by fluorescence confocal polarizing microscopy. We demonstrate that the finite surface anchoring at the bounding plates plays a crucial role in the system behavior both near and well above ...


Magnetic-Field Effect On Periodic Stripe Domains In Nematic Liquid-Crystals, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi Jan 1995

Magnetic-Field Effect On Periodic Stripe Domains In Nematic Liquid-Crystals, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi

Chemical Physics Publications

Hybrid aligned nematic films placed onto an isotropic fluid substrate exhibit an unusual periodic stripe domain structure that appears only when the thickness of the film is smaller than a few tenths of a micrometer. We investigated the effect of a magnetic field on the threshold between the periodic stripe domains and the aperiodic deformed structure of the director. As experimentally observed, a magnetic field applied along the stripe domains favors a nonperiodic state with the director undistorted in the horizontal plane. The experimental findings are confirmed by a theory that takes into account not only the usual type of ...


Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik Aug 1994

Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik

Chemical Physics Publications

To verify the status of the divergence K13 term in the elastic theory of liquid crystals we study submicron films placed onto an isotropic fluid substrate in the Langmuir trough (Langmuir liquid crystal, LLC). The upper and lower surfaces favor normal and tangential molecular orientation, respectively. The periodic domain phase is observed in a nematic LLC. The dependence of the periodicity L of the domains vs film thickness h can be explained only if the elastic energy is accompanied by divergence terms with nonzero constants K13 and K24. It is found that for 5CB K13 almost-equal-to -0.2K11.


Periodic Stripe Domains And Hybrid-Alignment Regime In Nematic Liquid-Crystals - Threshold Analysis, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi Feb 1994

Periodic Stripe Domains And Hybrid-Alignment Regime In Nematic Liquid-Crystals - Threshold Analysis, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi

Chemical Physics Publications

Recently we investigated the occurrence of static periodic stripes in a hybrid aligned nematic cell. Assuming that the tilt anchoring was stronger at the planar wall than at the homeotropic wall, we have found the critical thickness of the cell for the transition from planar to periodic alignment as a function of the surface energy in the presence of a magnetic field. Here we study, for the same kind of cell, the critical thickness between the periodic and the aperiodic deformed structure by means of an appropriate numerical technique. As expected, such a threshold was found to be greater than ...