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Structure, wettability, and barrier properties of self-assembled monolayers on metallic surfaces.

机译：金属表面上自组装单分子膜的结构，润湿性和阻隔性能。

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Self-assembled monolayers (SAMs) offer a convenient approach for fabricating molecularly tailored interfaces with well-defined compositions, structures, and thicknesses. SAMs have been suggested for use as corrosion barriers, antifouling coatings, and as components of molecular electronics and lithography. Still, researchers lack the molecular description of the interfacial properties, structural features, and barrier properties of SAMs that would be useful for optimizing and tailoring the behavior of SAMs. This dissertation makes connections between the molecular level structural features of SAMs and macroscopic properties such as wettability and barrier properties using molecular dynamics (MD) simulations and experimental techniques.; MD simulations were performed to explain the unexpected experimental observation that the wetting properties of some liquids on SAMs prepared using alkanethiols (CnSH) depend on whether the chain length (n) is odd or even. The difference in near-surface structure of the liquid (and not that of reorganization events by the monolayer) appears responsible for the high sensitivity of hexadecane and the general insensitivity of water to the structural differences expressed by odd- and even-chained monolayer surfaces.; MD simulations were also performed to investigate the influences of molecular structure on the ability of n-alkanethiolate SAMs on gold and copper to act as barrier films against through-film oxygen transport as relevant to the uses of these films in corrosion inhibition. The barrier resistances offered by these films towards oxygen transport, as calculated by the MD simulations, were a function of the crystallinity of the center region of the SAMs. Upon the introduction of an ether linkage within the SAM, the results from MD simulations show that when the ether linkage is too close to the metal surface or to the chain ends, the free energy barrier of SAMs towards oxygen diffusion was almost 10 kJ/mole less than that for an n-alkanethiolate SAM having the same chain length.; Phytanylthiol (3, 7, 11, 15-tetramethyl-hexadecanethiol) SAM on gold was characterized by ellipsometry, wetting measurements, X-ray photoelectron spectroscopy, and MD simulations to gain insights into the effect of a branched chain on the thickness, chain packing and orientation, wettability, and barrier properties of a SAM. These experimental and computational studies indicate that phytanylthiolate SAM on gold contains a fully extended 16-carbon backbone which is more disordered as compared to n-hexadecanethiolate monolayer on gold, with the sulfur head group possibly occupying four-fold hollow sites on gold.
机译：自组装单层（SAM）提供了一种方便的方法来制造具有明确定义的成分，结构和厚度的分子定制界面。已建议将SAM用作腐蚀屏障，防污涂料以及分子电子学和光刻的组件。尽管如此，研究人员仍缺乏分子对SAM的界面特性，结构特征和阻隔性能的分子描述，这对于优化和定制SAM的行为非常有用。本文利用分子动力学（MD）模拟和实验技术，将SAM的分子结构特征与宏观性质如润湿性和阻隔性联系起来。进行MD模拟以解释意想不到的实验观察结果，即使用链烷硫醇（CnSH）制备的SAM上某些液体的润湿特性取决于链长（n）是奇数还是偶数。液体近表面结构的差异（而不是单分子层的重组事件的差异）似乎是造成十六烷的高敏感性和水对由奇数和偶数链状单分子层表面表示的结构差异的总体不敏感性的原因。 ;还进行了MD模拟，以研究分子结构对金和铜上的正链烷硫醇SAM的能力的影响，金和铜用作阻挡膜阻止膜中的氧气传输，这与这些膜在腐蚀抑制中的用途有关。如通过MD模拟计算的，这些膜提供的对氧传输的阻挡电阻是SAM的中心区域的结晶度的函数。在SAM中引入醚键后，MD模拟的结果表明，当醚键太靠近金属表面或链端时，SAMs对氧扩散的自由能垒几乎为10 kJ / mole小于具有相同链长的正链烷硫醇盐SAM。黄金上的苯丙硫醇（3,7,11,15-四甲基十六烷硫醇）SAM的特征在于椭圆偏光法，润湿测量，X射线光电子能谱和MD模拟，以深入了解支链对厚度，链堆积的影响SAM的取向，润湿性和阻隔性能。这些实验和计算研究表明，金上的植烷硫醇盐SAM包含一个完全延伸的16碳主链，与金上的正十六烷硫醇单分子层相比，杂乱无章，硫头基可能占据金的四倍空心位点。

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