https://doi.org/10.1140/epje/e2005-00019-8
Regular Articles
Selective imaging of 3D director fields and study of defects in biaxial smectic A liquid crystals
1
Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA
2
Raman Research Institute, 560080, Bangalore, India
* e-mail: odl@lci.kent.edu
Received:
16
October
2003
Published online:
22
February
2005
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 perpendicular to the lamellae and the director
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
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
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
parallel to the smectic layers. The FCDs in SmAb
can be associated with topologically non-trivial configurations of
in the surrounding matrix that are equivalent to the disclination lines.
© EDP Sciences/Società Italiana di Fisica/Springer-Verlag, 2005