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首页> 外文学位 >Two-dimensional structures and order of nano-objects on the surface of water: Synchrotron x-ray scattering studies.
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Two-dimensional structures and order of nano-objects on the surface of water: Synchrotron x-ray scattering studies.

机译：水表面纳米物体的二维结构和顺序：同步加速器X射线散射研究。

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Surface-sensitive synchrotron x-ray scattering techniques have been used to study the microscopic two-dimensional (2D) structures of Langmuir monolayers (LMs) formed by various nano-meter sized macromolecules on water at room temperature. The molecules studied are: sphere-like fullerene-propylamine adduct (C60-PA); rod-like α-helical polypeptide poly(γ-benzyl-L-glutamate) (PBLG); hairy-rod polypeptide poly(γ-4-(hexadecyloxy)benzyl α,L-glutamate) (C16-O-PBLG); and sphere-like gold nanoparticles derivatized with carboxylic acid-terminated alkylthiol chains (AuSC16). PBLG and C16-O-PBLG rods lie down parallel to the interface and align locally with neighboring rods within the monolayer plane.; The observations of broad grazing incidence diffraction (GID) peaks indicate that the C60-PA and AuSC16 monolayers are 2D amorphous solids that are consistent with local hexagonal packing. They possess only short-range positional order with lateral correlations extending over no more than a few nearest-neighbor distances. The large number of electrons contained in the molecules makes the observations of liquid-like 2D x-ray structure factors possible.; The surface pressure versus area isotherm and specular reflectivity (XR) measurements confirm that both the LMs of rod-like PBLG and sphere-like AuSC16 undergo a first-order monolayer/bilayer transition upon lateral compression. In both cases, off-specular diffuse scattering (XOSDS) intensities from compressed monolayers are consistent with the presence of capillary waves on the surface and the lateral homogeneity of the films. However, both PBLG and AuSC16 bilayers exhibit excess off-specular scattering above the predicted capillary contribution, indicating that the bilayers are microscopically inhomogeneous. The results demonstrate the utility of XOSDS techniques for probing inhomogeneities on liquid surfaces.; Due to the additional long alkyl side chains, the monolayers of hairy rod C16-O-PBLG sustain much higher surface pressures than PBLG and the monolayer/bilayer transition is suppressed. In C16-O-PBLG LM, hydrophobic side chains are segregated towards the film/gas interface, while the PBLG cores reside closer to the water/film interface. The two high-angle GID peaks observed at high surface pressures are consistent with a common packing mode of alkyl chains known as the herringbone (HB) packing. One of the peaks is absent at low surface pressures, suggesting that the HB order is first established by the side chains that are confined one-dimensionally between aligned PBLG cores.
机译：表面敏感的同步加速器X射线散射技术已用于研究室温下由各种纳米尺寸的大分子在水中形成的Langmuir单层（LM）的微观二维（2D）结构。研究的分子是：球形的富勒烯-丙胺加合物（C60-PA）；棒状α-螺旋多肽聚（γ-苄基-L-谷氨酸）（PBLG）；毛杆多肽聚（γ-4-（十六烷氧基）苄基α，L-谷氨酸）（C16-O-PBLG）;以及球形的金纳米颗粒，这些纳米颗粒被羧酸封端的烷基硫醇链（AuSC16）衍生。 PBLG和C16-O-PBLG杆平行于界面向下放置，并与单层平面内的相邻杆局部对齐。宽掠入射衍射（GID）峰的观察结果表明，C60-PA和AuSC16单层是2D无定形固体，与局部六边形堆积一致。它们仅具有短距离的位置顺序，横向相关性延伸的距离不超过几个最近的距离。分子中包含的大量电子使观察液体状的二维X射线结构因子成为可能。表面压力与面积等温线和镜面反射率（XR）的测量结果证实，棒状PBLG和球形AuSC16的LM在横向压缩时都会经历一阶单层/双层转变。在这两种情况下，压缩单层的镜外反射散射强度（XOSDS）与表面毛细波的存在和薄膜的横向均匀性是一致的。但是，PBLG和AuSC16双层都在预期的毛细管作用之上显示出过量的镜外散射，表明双层在显微镜下是不均匀的。结果证明了XOSDS技术可用于探测液体表面的不均匀性。由于额外的长烷基侧链，长毛杆C16-O-PBLG的单层比PBLG承受更高的表面压力，并且抑制了单层/双层的转变。在C16-O-PBLG LM中，疏水性侧链偏向薄膜/气体界面，而PBLG核则更靠近水/薄膜界面。在高表面压力下观察到的两个高角度GID峰与称为人字形（HB）堆积的烷基链的常见堆积模式一致。在低表面压力下不存在其中一个峰，这表明HB顺序首先由一维限制在对齐的PBLG核之间的侧链建立。

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