Inversion walls in homeotropic nematic and cholesteric layers
作者:
J.M. GILLI,
S. THIBERGE,
A. VIERHEILIG,
F. FRIED,
期刊:
Liquid Crystals
(Taylor Available online 1997)
卷期:
Volume 23,
issue 5
页码: 619-628
ISSN:0267-8292
年代: 1997
DOI:10.1080/026782997207894
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
We describe the experimental properties of metastable domains associated with the presence of an Inversion Wall (IW) and observed with homeotropically anchored nematic and cholesteric liquid crystals sandwiched between parallel glass plates. Such a distorted situation, stabilized by the application of an electric field parallel to the plates as described in reference [1], can also be obtained transiently either when filling a sample cell by capillarity or in some studies of directional solidification at the N-I interface [2]. The application of an electric field perpendicular to the plates with Delta epsilon 0 materials allows control of the reversal region thickness in the bulk of the sample and its associated birefringence. This IW can be stabilized in the particular case of low lateral extension globules in which the line tension of the looped disclination separating the pi wall regions from the homeotropic regions counterbalances the unfavourable bulk free energy. Particular attention is devoted to the defects of these walls, whose appearance using polarizing microscopy is similar to the umbilics of the Freedericksz transition. The structure of these 'four brush' defects is nevertheless here singular, corresponding to point defects of a 3D uniaxial nematic medium. In the case of a chiral nematic, these IW undergo a particular undulation instability which is also observed in 2D simulations.
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