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

本研究的目的是用同步辐射X射线微束散射法研究(反)铁电液晶中的局域层结构与局域分子有序或取向之间的关系。近晶液晶盒中观察到的织构大小不一，大小从几个μm到几十个pm不等，对应于晶盒厚度。为了研究详细的结构，研制了具有适当性能(空间分辨率、角度发散和强度)的X射线光学器件。通过研制可弯曲的非球面反射镜系统，X射线微束可以从几个μm到30~40μm。小束对高分辨率实验是有效的，而大束流则适合于中等辐射损伤的快速数据采集。用X射线微束研究了层内分子有序和层结构本身。利用高分辨率的大面积X射线CCD探测器，成功地测量了三角形和矩形电场作用下电倾斜液晶的时间分辨晕图。我们还首次成功地测量了由弯曲型分子组成的液晶小区域的共振X射线散射。由于共振X射线散射强度较弱，而液晶本身又容易受到强的高密度X射线的破坏，因此我们研究了最佳的束流大小和X射线光子密度条件。此外，采用高空间分辨率的X射线CCD相机，获得了高精度的层间距。根据这些观察结果，讨论了层内和层间的分子相互作用。

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.