0428同步年報-2021-全

034 ACTIVITY REPORT 2021 Fig. 3 : Microbeam SAXS analysis along several radial-direction spots of a PHB spherulite crystallized from PHB/PEO (75/25) at T c = 50 °C (band spacing ≈ 27 µm): (a) POM image, (b) 2D-SAXS patterns, and (c) intensity profiles at various positions (1, 2, 3, 4) in PHB/PEO spherulite. [Reproduced from Ref. 1] Fig. 4 : Summary of POM, SEM, microbeam X-ray SAXS results, and a schematic for grating structure for periodic banded PHB. [Reproduced from Ref. 1] Spots 1–4. The SAXS pattern indicates that, in Spots 2 and 4, there are signs with respect to electron densitycontrast between crystalline and amorphousphasesin the vertical lamellae in a ridge as shown earlier in Fig. 2(c) . As signals of Spots 1 and 3 are weak, these signals can be regarded as no signal, indicating that the lamellae on Spots 1 and 3, respectively, are mostly normal to the X-ray beam (thus horizontal to the substrate). The periodic morphology and optical changes in the ring bands are caused not by the thickness of individual lamellae in ridge versus valley bands but result from crystal assembly and orientation. The valley region is dominated with flat- on crystals; the ridge region is packed mainly with edge-on crystals. Similarly, in SAXS, a X-ray beam perpendicular to the lamellae results in a poor contrast of electron density between amorphous and crystalline regions; so there is no, or only weak, signal observed in Spots 1 and 3. Thicker films produce more intense birefringence patterns due to more pronounced anisotropic crystals in varied orientations. In this work, the film thickness of PHB was kept at ≈20 ± 2µm, so alternate blue and orange birefringence rings are respectively associated with the ridge and valley bands seen in POM. In the ridges, the lamellae are oriented perpendicularly to the micro-beam X-rays as well as to the optical axis in POM. This perpendicular arrangement of the lamellae induces signals on Spots 2 and 4. Furthermore, SAXS maximum azimuthal angles 145°and 290° confirm that the edge-on lamellae in ridges are mostly mono-axially oriented in Fig. 2(c) . In summary, Fig. 4 shows that a detailed 3D assembly in the periodic ring PHB crystal aggregates is proved by delicate microscopic techniques, assisted with synchrotron X-ray analysis and supported by direct evidence of morphology dissection; the grating architecture of the periodic PHB aggregates possesses a novel property of photonic-crystal iridescence, which was never reported or discovered before for such polymeric crystals. NSRRC synchrotron microbeam SAXS sources and various microscopic techniques were used to analyze the PHB crystal aggregates on specific spots of the banded spherulites. Through X-ray microbeam 2D-SAXS, this critical proof reinforces that the lamellar assembly in the PHB- banded periodic architectures are such that the optical-blue bands are packed mainly by grating normally oriented strut-crystals periodically interfaced with horizontally oriented rib-crystals. The grating structure with alternate strut-rib assembly in the banded PHB resembles many natural iridescent crystals, and is further proved with striking photonic reflections as a critical novel finding. (Reported by Eamor Woo, National Cheng Kung University) This report features the work of Eamor Woo and his collaborators published in Macromol. Rapid Commun. 42 , 2100281 (2021). TPS 25A Coherent X-ray Scattering • XPS, NEXAFS, UPS • Materials Science, Chemistry, Surface, Interface and Thin- film Chemistry, Condensed-matter Physics References 1. Y.-H. Liao, S. Nagarajan, E. M. Woo, W.-T. Chuang, Y.-W. Tsai, Macromol. Rapid Commun. 42 , 2100281 (2021). 2. S. Nagarajan, E. M. Woo, Polymer 188 , 122141 (2020).