Characterization of local molecular ordering and the layer structure of smectic liquid crystals by synchrotron micro-beam scattering

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The purpose of the present study is to clarify the relation between the local layer structure and the local molecular ordering or orientation in (anti-) ferroelectric liquid crystals by synchrotron X-ray micro-beam scattering.Experiments have been performed on the beam-line 4A at the Photon Factory, Institute of materials structure science, KEK, using synchrotron radiation from a bending magnet. The textures observed in the smectic liquid crystal cells are in various sizes from a few μm to a few tens of pm corresponding to the cell thickness. In order to investigate the detailed structure, X-ray optics having appropriate performance (spatial resolution, angular divergence and intensity) were developed. By developing the bendable aspherical mirror system, X-ray micro-beams from a few μm to 30〜40 μm are now available. The small beam is effective for the high resolution experiment while the larger beam is suitable for the rapid data acquisition with the moderate radiation damage.The molecular ordering in the layer and the layer structure itself were investigated with X-ray micro-beams. With a high resolution large area X-ray CCD detector, we have succeeded in the measurement of the time resolved halo pattern from the electroclinic liquid crystal under the triangular and rectangular electric field. We have also succeeded in the measurement of resonant X-ray scattering from the small region of the liquid crystal consisting of bent type molecules, for the first time. Since the intensity of the resonant X-ray scattering is weak, whereas the liquid crystal itself is damaged easily with strong high density X-rays, we have investigated the optimum conditions of the beam size and the X-ray photon density. Furthermore, with an adoption of the high spatial resolution X-ray CCD camera, we have obtained the layer spacing with high accuracy. From these observations, the intra- and inter-layer molecular interactions were discussed.