Clarification of Order Structure Peculiar to the Near-surface Region of Crystalline Polymer Films and Dynamics on their Structural Formation

通过同步加速器掠入射x射线衍射（SR-GIXD）和掠入射小角x射线散射（SR-GISAXS）测量，我们成功地研究了晶体聚合物在狭窄空间（如表面和薄膜）中特有的链状和片层状堆积结构。以高密度聚乙烯（HDPE）对二甲苯溶液为基材，采用浸涂法在硅片上制备了厚度约400 nm的薄膜。将浸涂膜和HDPE体样品在氮气气氛下等温结晶或在不同温度下退火。为了在薄膜的近表面和块体区域检测Bragg衍射，在spring8 （Hyogo, Japan）的BL13XU光束线上，在小于临界角（α_c）的x射线入射角（α_i）下进行了面内GIXD测量。结果表明，正交晶胞近表面的晶格常数a和b均小于体区晶格常数，但大于体区晶格常数。这意味着在样品制备过程中，由于PE和硅之间的热膨胀系数存在较大的不匹配，导致了单元胞的变形，特别是在PE和硅之间的界面区域。另一方面，对薄膜的实晶晶格分析表明，近表面区域的长、短程晶格畸变比体区大。这可能与薄膜的表面自由能和/或从表面释放潜热有关。SR-GISAXS对SPring-8的BL40B2光束线α_i小于α_c的x射线进行了测量。利用成像增强器和CCD探测器或成像板在300K下检测真空电池中薄膜的2D-GISAXS图案。所有薄膜在Yoneda峰附近均有较强的面内散射。从散射峰位置可以看出，长周期，即堆叠晶体片间的平均距离约为25 ~ 30 nm。从GIXD数据可以看出，链在薄片中相对平行于表面。结合GIXD和GISAXS数据表明，相对边缘朝上的片层在与表面平行的方向上堆叠。退火后，在近表面区域发生了明显的部分熔化和再结晶。少

We have successfully investigated chain and lamellar packing structures peculiar to crystalline polymers confined to narrow space, such as the surface and the thin film, by synchrotron grazing-incidence X-ray diffraction (SR-GIXD) and grazing-incidence small-angle X-ray scattering (SR-GISAXS) measurements. Thin films with a thickness of ca. 400 nm were prepared on silicon wafers from a p-xylene solution of high-density polyethylene (HDPE) by a dip-coating method. The dip-coated films and HDPE bulk samples were isothermally crystallized from the melt or annealed at various temperatures under nitrogen atmosphere.In order to detect Bragg diffractions from the near-surface and bulk regions of the thin films, in-plane GIXD measurements were carried out at incident angles (α_i) of X-rays smaller and lager than the critical angle (α_c) at the BL13XU beamline of SPring-8 (Hyogo, Japan). It was revealed that the lattice constants a and b of orthorhombic unit cell in the near-surface region of t … More he thin film were smaller than those in the bulk region but larger than those of the bulk samples. This implied that the unit cell especially in the interfacial region between PE and silicon was distorted during sample preparation due to large mismatching between their thermal expansion coefficients. On the other hand, pracrystalline lattice analysis for the thin films indicated that long and short-range lattice distortion was larger in the near-surface region than in the bulk region. This might be related with the surface free energy of the film and/or releasing the latent heat from the surface.SR-GISAXS measurements were carried out at α_i of X-rays smaller and lager than the α_c at the BL40B2 beamline of SPring-8. The 2D-GISAXS patterns from the films placed in a vacuum cell were detected at 300K with an imaging intensifier and a CCD detector or an imaging plate. Strong scattering in the in-plane direction near Yoneda peak were detected for all of the films. From the peak position of the scattering, it was found that the long period, the average distance between stacked crystalline lamellae, was ca.25-30 nm. From the GIXD data, it was implied that chains were relatively oriented parallel to the surface in the lamellae. Combination of GIXD and GISAXS data indicated that relatively edge-on oriented lamellae were stacked in the parallel direction to the surface. By annealing, partial melting and recrystallization might occur remarkably in the near-surface region. Less