Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

4A/2004G337

Molecular Orientation and Layer Structure in Electroclinic Liquid Crystals byTime Resolved X-ray Micro-Diffraction
Atsuo IIDA1*, Yumiko TAKAHASHI2, Yoichi TAKANISHI3 and Hideo TAKEZOE3
1
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
2
Nihon University, Surugadai, Kanda, Chiyoda-ku, Tokyo 101-8308, Japan3
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama,Meguro-ku, Tokyo 152-8552, Japan
Introduction
The electroclinic effect has attracted much attention asa pre-transition phenomenon in the chiral smectic A(SmA) phase near the SmA-Smectic C* (SmC*) phasetransition. With the application of an electric field along
the layer, SmA molecules tilt in a plane perpendicular to
the applied field. The molecular response in theelectroclinic effect has been discussed based on theelectro-optical measurement in which the h-chevron(book shelf structure) is assumed. To observe thedynamic response of the local layer structure in thesmectic liquid crystal under the external field, timeresolved synchrotron X-ray micro- diffraction has beensuccessfully used [1]. In the previous study [2], it isrevealed that the vertical-chevron is realized at the low
electric field while the compound chevron which consistsof vertical-chevron and the horizontal-chevron isgenerated at the high field. In this report, the temporaland spatial distributions of the molecular orientation as
well as the layer structure is analyzed directly by the time
resolved high-angle micro X-ray halo pattern together
with the small angle layer reflection in the electroclinic
effect.
Experimental
The experiment was carried out on BL-4A. The x-ray
energy was 14.3 keV and the beam size was about 3×4µm2. The diffracted intensity was measured by an image
intensified X-ray CCD camera as functions of time andposition.
The sample was a FLC, TK-C101 (Chisso),
sandwiched between ITO-coated glass plates rubbed oneside after coating polyimide. The cell gap was about
6~7µm.
The sample was kept at Tc+1°C duringexperiments, where Tc, SmA*→SmC* transition
temperature, was 56°C [3].
Results and Discussion
A bipolar rectangular wave form electric field (5 Hz)
was applied to the sample. Fig.1 shows the time resolved
x-ray micro X-ray halo pattern obtained at +13V. The
halo-pattern is due to the intra-layer order of themolecular arrangement while two sharp peaks near thecenter of an image are due to the local layer structure.
From the halo-pattern and the small angle scattering
pattern, the close relation between the molecularorientation and the layer structure can be discussed. Fig.2

172

Users' Reportshows the spatial variation of the molecular orientation
normal to the rubbing direction. The spatial period isabout 10 µm which well corresponds to the stripe texture.
The amplitude is about 3~4 degrees which is smaller thanthe layer deflection angle obtained from the layer
reflection. The temporal variation of the molecularorientation was also measured. Further experiment withhigher precision is now under way.

Fig.1 Time resolved micro Xray halo patterns (short arcs atthe upper and lower sides)
together with small angle layer
reflections (right and left) insideafter the background subtraction
process. Spotty concentric rings
are due to the thin film
electrodes. Note that a circularabsorber was inserted in the central region to avoid thesaturation of the CCD camera. Darker regions correspondto higher X-ray intensities.

Fig.2 Peak angular positions of the halo pattern as afunction of position for the bipolar electric field.
References[1] Y.Takahashi et al. Phys. Rev. E67 (2003) 051706[2] A.Iida et al., to be published in Liquid Crystals[3]A.Iida et al., Photon Factory Activity Report #21(2003) 150*atsuo.iida@kek.jp