As the beam size is small, it is very important to confirm the irradiated area of the X-ray microbeam on samples. An optical microscope, which was set on the X-ray beam path, was used to align the sample position roughly. However, more precise alignment of the X-ray microbeam is very difficult using optical microscope for smaller samples such as a polymer single fiber. In this study, we proposed a novel technique by the Thomson scattering method for the precise alignment of the X-ray microbeam position as shown in Fig. 1. Figure 2 shows the intensity profile of Thomson scattering from a Kevlar 29 single fiber (fiber diameter ca. 12 μ m ) . O ne-dimensional scans were performed perpendicular to the fiber a x is. The intensity of the Thomson scattering is proportional to the number of electrons at the regions where the X-ray penetrated the sample. W ith changing sample position ((a ) -(d )) , X-ray diffraction patterns were detected using an imaging plate as shown in Fig. 3 . The X-ray e x posure time was 600 s per pattern. J udging from the spot-li k e equatorial reflections (11 0 and 2 00 reflections ) , the degree of the molecular orientation of the s k in region (Fig. 3 (a )) is higher than that of the core region (Fig. 3 (d )) . Fig. 2. Intensity profile of Thomson scattering from Kevlar 29 single fiber. Sampling steps of 0.5 μ m/point were employed. Microanalysis for Polymer Materials by X-ray Microscopes P olymer fibers have e x cellent mechanical properties and are light in spite of their fle x ibility, so they are widely used as clothing, nonwoven fabric, reinforced fiber for advanced composite materials and so on. G enerally, polymer fibers are obtained from a polymer solution or a molten polymer by the spinning method at above the melting point of the polymer. This process would form a gradual structure in the radial direction of a polymer fiber, because solidification occurs from the outer region of the polymer fiber during coagulation in poor solvents or during the cooling process. Therefore, a polymer fiber has different microstructures between the outer region and the inner region. The unique microstructure of a polymer fiber is called the s k in / core structure. R ecently, with the development of microscopic processing techniques, precise measurement for the structural analysis of very small area s has become increasingly important. The X-ray diffraction method has been widely used for the structural analysis of polymer materials. The transmission electron diffraction method requires a thi n sample and a high - vacuum condition. However, no special pretreatment of samples is required for the X-ray diffraction method. An X-ray microbeam of 1 0 k e V was obtained using a phase zone plate , which was made of tantalum at beamline BL24XU [ 1 ] . A rhodium-coated plane mirror was introduced in the upstream of the e x perimental hutch in order to eliminate higher order B ragg reflections properly for different photon energies. The focused beam size at the sample position was evaluated to be 1.1 μ m (vertical ) × 1. 3 μ m (horizontal ) by the k nife-edge method. Fig. 1. Schematic representation of the X-ray microdiffraction method for the polymer single fiber. The sample holder was fixed on the high-precision sample stage and the fiber axis was aligned in the horizontal direction. Polymer single fiber 0.0625 μ m/pulse SSD X-ray microbeam Zone plate (a) (b) (c) (d) 12 μ m Intensity (a.u.) Position ( μ m) -15 -10 -5 0 5 10 15 41 Masaru Kotera a , Takashi Nishino b and Yasushi Kagoshima c (a) SPring-8 / JASRI (b) Kobe University (c) Himeji Institute of Technology University E-mail: mkotera@spring8.or.jp References [1] Y. Kagoshima et al. : Nucl. Instrum. Meth. A 467- 468 ( 200 1) 8 72 . [ 2 ] M. G . D obb et al. : J. Polym. Sci., Polym. Phys. Ed. 15 (1 977 ) 220 1. [ 3 ] M. Panar et al. : J. Polym. Sci., Polym. Phys. Ed. 21 (1 9 8 3 ) 476 1. Fig. 4. Equatorial diffraction profiles of Kevlar 29 single fiber at different measurement points along the fiber axis. (a) (b) (c) (d) Diffraction angle 2 θ (degree) 5 10 15 20 25 30 (110) (200) skin core Intensity (a.u.) (a) (b) (c) (d) 12 μ m -15 -10 -5 0 5 10 15 Position ( μ m) Intensity (a.u.) Fiber axis a d Fig. 3. X-ray fiber pattern of Kevlar 29 single fiber. (a) skin region and (d) core region. F igure 4 sho w s the e q uatorial diffraction profiles of the Kevlar 29 single fiber at different points ((a)-(d) in F ig. 1) along the fiber a x is. In the core region (d) of the single fiber, the peak intensity is I 110 < I 200 . Ho w ever, they are reversed w hen approaching the skin region (a), that is, the peak intensity of 11 0 reflection gradually i n c r e a s e d a s t h e m e a s u r e m e n t position approached the skin layer. This implies that the b-a x is of the Kevlar crystal, w hich is the direction of a hydrogen bond, is oriented in the radial direction of the fiber [ 2 , 3 ]. According to these results, the X - r a y m i c r o d i f f r a c t i o n m e t h o d demonstrated to be a po w erful tool for the structural analysis of small areas for polymer materials. 42
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