Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

4A/2004G337

Director configuration in the vicinity of defect lines in nematic Schlieren textureby X-ray Micro-Diffraction
Atsuo IIDA1*, Yumiko TAKAHASHI2, Yoichi TAKANISHI3, Youko OHTSUKA3and Hideo
TAKEZOE3
1
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
2
Dept.Phys., Col.Sci.Tech., Nihon Univ., Surugadai, Kanda, Chiyoda-ku, Tokyo 101-8308, Japan
3
Dept. Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku,
Tokyo 152-8552, Japan
Introduction
In nematic liquid crystals between glass plates, thedirector usually orients parallel to the substrates. If thisorientation is not homogeneous, so-called Schlieren
textures are observed between crossed polarizers asshown in Fig.1, in which the brushes are two fold at
singular points.
This singularity corresponds to a
topological defect. From the micrograph, both defects arewedge disclinations in nature and are assigned strengths=±1/2. The disclination is the typical defect in nematicand its characterization has been made by the opticalmethod. X-ray scattering from the nematic sample showsthe oriented halo-pattern which shows the orientation of
the director and the order parameter. In the present report,
we have demonstrated the characterization of theSchlieren texture with an X-ray micro-scatteringexperiment.

Results and Discussion
Fig.2 shows a series of diffraction patterns around thesingular point shown in Fig.1. The central part of eachdiffraction pattern was covered with a direct beam stop.
The raw data was subtracted by background scatteringfrom the cell without a sample. From each diffraction
pattern, the director orientation can be uniquelydetermined as shown in Fig.3. It is clearly shown that thedirector rotates by π around the singular point and its
strength is s = -1/2 from the rotation direction. The orderparameter can be also determined from analysis of eachhalo pattern. It is also noted that the halo patter at thecenter loses the clear orientation partly due to the specificstructure of the singular point. Micro X-ray scattering
study can reveal specific characteristics of the Schlieren
texture.

Experimental
The experiment was carried out on BL-4A. The x-ray
energy was 14.2 keV and the beam size was about 2×32µm . The diffraction pattern was measured by an image
intensified X-ray CCD camera (6 in. in dia.) as a functionof position. The sample to the camera distance was 16 cm.
The sample was a nematic 5CB sandwiched between
glass plates. The cell gap was about 25 µm. The sample
was kept in the nematic phase at room temperature.

Fig.2 A series of X-ray diffraction patterns from the region of
the specimen within the dashed rectangular (12 µm x 20 µm
region) in Fig.1. 2 µm / step and 5 µm / step in the horizontal
and vertical directions, respectively.

50 µmFig.1 Schlieren texture of a nematic phase under planaranchoring condition by a polarising optical microscopeattached to the X-ray micro-beam system. The curved
brushes converge into singular point defects.

Fig.3
Director orientation
around thesingular point
deduced from Fig.2.
Theorientation
wellcorresponds to brushes of themicrograph in Fig.1*atsuo.iida@kek.jp

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