Molecular aggregation state of surface-grafted poly{2-(perfluorooctyl)ethyl acrylate} thin film analyzed by grazing incidence X-ray diffraction
Molecular aggregation state of surface-grafted poly{2-(perfluorooctyl)ethyl acrylate} thin film analyzed by grazing incidence X-ray diffraction
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DOI：
10.1295/polymj.pj2008107
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发表时间：
2008-09
期刊：
影响因子：
2.8
通讯作者：
H. Yamaguchi;K. Honda;M. Kobayashi;M. Morita;H. Masunaga;O. Sakata;S. Sasaki;A. Takahara
中科院分区：
文献类型：
--
作者：
H. Yamaguchi;K. Honda;M. Kobayashi;M. Morita;H. Masunaga;O. Sakata;S. Sasaki;A. Takahara
在平面硅片上对丙烯酸 2-(全氟辛基)乙酯进行表面引发原子转移自由基聚合，得到分别具有 4、11 和 43 nm 三种不同厚度的聚{2-(全氟辛基)乙基丙烯酸酯} (PFA-C8) 刷薄膜。 PFA-C8刷表面的水接触角为120°。通过X射线反射率(XR)、广角X射线衍射和掠入射X射线衍射(GIXD)测量来分析PFA-C8刷的全氟烷基(Rf)基团的分子聚集状态。 XR分析表明，空气/刷子界面处的Rf基团形成致密结构，而刷子/基材界面处产生相对低密度的区域。在qxy=12.5 nm−1处观察到厚度为11和43 nm的刷膜的面内GIXD峰值，这表明最外表面的Rf基团垂直于硅衬底表面取向。在 43 nm 厚的 PFA-C8 刷膜的面外衍射图中，观察到与双层片层的周期长度相对应的峰。因此，较厚的刷膜的Rf基团结晶并在最外表面形成有序的双层层状结构。相反，通过WAXD和GIXD没有从厚度为4nm的PFA-C8观察到衍射图案。这些结果表明在刷/基底的界面处形成了非晶层。由于刷链末端固定在基底上，刷锚定区域的 Rf 基团无法形成足够有序的结构。这表明最外表面的 PFA-C8 刷薄膜中的 Rf 基团以与锚定区域中的 Rf 基团不同的方式聚集。
Surface-initiated atom transfer radical polymerization of 2-(perfluorooctyl)ethyl acrylate on a flat silicon wafer was carried out to give poly{2-(perfluorooctyl)ethyl acrylate} (PFA-C8) brush thin film with three different thicknesses of 4, 11, and 43 nm, respectively. The water contact angle of the PFA-C8 brush surface was 120°. The molecular aggregation state of the perfluoroalkyl (Rf) group of PFA-C8 brush was analyzed by X-ray reflectivity (XR), wide-angle X-ray diffraction, and grazing incidence X-ray diffraction (GIXD) measurements. XR analysis revealed that Rf groups at the air/brush interface formed a densely packed structure, while a relatively low-density region was generated at the brush/substrate interface. The peaks of in-plane GIXD for brush films with thicknesses of 11 and 43 nm were observed at qxy=12.5 nm−1, which indicated that Rf groups at the outermost surface oriented perpendicular to the surface of silicon substrate. In an out-of-plane diffraction profile of the 43 nm-thick PFA-C8 brush film, peaks corresponding to a periodic length of the bilayer lamellae were observed. Therefore, Rf groups of the thicker brush film were crystallized and formed ordered bilayer lamellar structure at the outermost surface. In contrast, no diffraction pattern was observed from the PFA-C8 at a thickness of 4 nm by WAXD and GIXD. These results indicate that an amorphous layer was formed at the interface of the brush/substrate. The Rf groups at the anchoring region of the brush could not form a sufficiently ordered structure due to immobilization of brush chain ends on the substrate. It was suggested that the Rf groups in a PFA-C8 brush thin film at the outermost surface aggregated in a different manner from those in the anchoring region.