Selective imaging of 3D director fields and study of defects in biaxial smectic A liquid crystals
Selective imaging of 3D director fields and study of defects in biaxial smectic A liquid crystals
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3D指向矢场选择性成像及双轴近晶A液晶缺陷研究
DOI：
10.1140/epje/e2005-00019-8
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
O. Lavrentovich
中科院分区：
文献类型：
--
作者：
I. Smalyukh;R. Pratibha;N. V. Madhusudana;O. Lavrentovich
Abstract.We report on the selective imaging of different director fields in a biaxial
smectic A (SmAb) liquid crystal using Fluorescence Confocal Polarizing
Microscopy (FCPM) and Polarizing Microscopy (PM). The patterns of two directors, namely the director $\hat{n}_a$ perpendicular to the lamellae and the director $\hat{n}_b$ in their planes are visualized by doping the liquid crystal with two fluorescent dyes with different orientation of the
transition dipoles with respect to the lamellar matrix. The properties of
defects such as disclinations and focal conic domains (FCDs) are consistent
with the non-polar D2h-symmetry of the SmAb mesophase in the
studied mixture of bent-core and rod-like molecules: ([see full textsee full text]) majority of defects
in the director $\hat{n}_b $ are half-integer “±1/2” disclinations;
([see full textsee full text]) the integer-strength “±1” defects tend to split into the “±
1/2” disclinations. We compare the vertical cross-sections of the “±1” disclinations in the $\hat{n}_b$ field in SmAb and uniaxial nematic samples. In SmAb, the “±1” disclinations do not escape
into the third dimension, while in the nematic samples with Schlieren
textures they do despite the surface anchoring at the plates; the
experimentally determined director field around the escaped disclination
capped by a pair of surface point defects – boojums matches the one
predicted recently [C. Chiccoli et al., Phys. Rev. E 66, 030701 (2002)]. The
FCD structure in SmAb is similar to that in SmA and SmC in terms of the
normal to the layers but differs significantly in terms of the director
field $\hat{n}_b$ parallel to the smectic layers. The FCDs in SmAb
can be associated with topologically non-trivial configurations of $\hat{n}_b$ in the surrounding matrix that are equivalent to the disclination lines.
