Monolayer/bilayer transition in Langmuir films of derivatized gold nanoparticles at the gas/water interface: An x-ray scattering study
Monolayer/bilayer transition in Langmuir films of derivatized gold nanoparticles at the gas/water interface: An x-ray scattering study
复制标题
DOI：
10.1063/1.1640334
复制
发表时间：
2004-02-15
影响因子：
4.4
通讯作者：
Lennox, RB
中科院分区：
文献类型：
--
作者：
Fukuto, M;Heilmann, RK;Lennox, RB
研究了衍生化金纳米颗粒Langmuir膜的微观结构与水表面面积/粒子的关系。该分子（AuSHDA）由平均核直径d约为22埃的金颗粒组成，这些金颗粒通过羧酸端接的烷基硫醇HS-(CH2)(15)- cooh稳定。薄膜的压缩导致表面压力与面积/颗粒等温线的有限压力的广泛平台，这与一级单层/双层转变相一致。x射线镜面反射率（XR）和掠入射衍射结果表明，当首次大面积/粒子扩散时，AuSHDA粒子在2维空间聚集，在a=34埃的最近邻距离上形成六边形排列的单层畴。与二维（2D）六边形顺序相关的横向位置相关性是短距离的，并且仅扩展到几个粒子间距离；这似乎是颗粒大小多分散性的结果。随后对薄膜的压缩增加了单层膜的表面覆盖率，但对密集区域的颗粒间距离影响不大。在单/双层共存平台附近的XR和非镜面漫射散射（XOSDS）结果与横向均匀的单层AuSHDA颗粒完全覆盖表面一致。在高原的高密度侧，从XR提取的电子密度剖面图清楚地显示了双层的形成，其中新形成的第二层比第一层的密度略小。与均匀的单层相比，从双层中观察到的XOSDS强度高于基于毛细波模型和均匀性假设的预测，表明双层中存在横向密度不均匀性。根据布拉格棒测量的结果，双层结构中两层的二维六边形顺序仅部分相关。(C) 2004年美国物理研究所。
The microscopic structure of Langmuir films of derivatized gold nanoparticles has been studied as a function of area/particle on the water surface. The molecules (AuSHDA) consist of gold particles of mean core diameter Dsimilar to22 Angstrom that have been stabilized by attachment of carboxylic acid terminated alkylthiols, HS-(CH2)(15)-COOH. Compression of the film results in a broad plateau of finite pressure in the surface pressure versus area/particle isotherm that is consistent with a first-order monolayer/bilayer transition. X-ray specular reflectivity (XR) and grazing incidence diffraction show that when first spread at large area/particle, AuSHDA particles aggregate two dimensionally to form hexagonally packed monolayer domains at a nearest-neighbor distance of a=34 Angstrom. The lateral positional correlations associated with the two-dimensional (2D) hexagonal order are of short range and extend over only a few interparticle distances; this appears to be a result of the polydispersity in particle size. Subsequent compression of the film increases the surface coverage by the monolayer but has little effect on the interparticle distance in the close-packed domains. The XR and off-specular diffuse scattering (XOSDS) results near the onset of the monolayer/bilayer coexistence plateau are consistent with complete surface coverage by a laterally homogeneous monolayer of AuSHDA particles. On the high-density side of the plateau, the electron-density profile extracted from XR clearly shows the formation of a bilayer in which the newly formed second layer on top is slightly less dense than the first layer. In contrast to the case of the homogeneous monolayer, the XOSDS intensities observed from the bilayer are higher than the prediction based on the capillary wave model and the assumption of homogeneity, indicating the presence of lateral density inhomogeneities in the bilayer. According to the results of Bragg rod measurements, the 2D hexagonal order in the two layers of the bilayer are only partially correlated. (C) 2004 American Institute of Physics.