The Adsorption on Platinum and Wettability of Monolayers of Terminally Fluorinated Octadecyl Derivatives
The Adsorption on Platinum and Wettability of Monolayers of Terminally Fluorinated Octadecyl Derivatives
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末端氟化十八烷基衍生物对铂的吸附及单分子层润湿性
DOI：
10.1021/j150554a004
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发表时间：
1957
期刊：
影响因子：
--
通讯作者：
W. Zisman
中科院分区：
文献类型：
--
作者：
E. G. Shafrin;W. Zisman
以前的润湿性研究得出的结论是，含有末端取代的三氟甲基基团的紧密堆积的极性分子的表面可能具有异常低的润湿性。末端氟化的十八胺和相应的酸被提出作为可能实现这一概念的合适化合物。通过从溶液中吸附并通过抽离法分离，在铂表面制备了末端氟化十八烷基衍生物的缩合单分子膜。比较了十八胺与三氟十八胺、硬脂酸与三氟硬脂酸的吸附性能。三氟十八胺达到吸附平衡所需的成膜时间比其他三种极性化合物长得多。疏水性的氟化胺的单分子膜很容易从水溶液中分离出来，但同样的方法应用于氟化酸却不成功。三氟甲基基团的引入导致润湿性的降低比从与全氟链烷酸的行为的比较中预期的要小。三氟十八胺的单层膜比三氟硬脂酸的单层膜更容易被有机液体吸收;而且，前者是疏水的，后者是亲水的。讨论了膜的吸附机理及膜的组成与润湿性的关系。在空间和电学考虑的基础上，可以得出结论，引入与CEVCHa-基团相关的强电偶极子足以抵消或抵消最初预期由引入三氟甲基产生的优势。
Previous wettability studies had led to the conclusion that unusually low wettability might be expected of a surface com-prising close-packed polar molecules containing terminally substituted trifluoromethyl groups. Terminally fluorinated octadecylamine and the corresponding acid were proposed as suitable compounds with which this concept might be realized. Condensed monolayers of terminally fluorinated octadecyl derivatives were prepared on platinum surfaces by adsorption from solution and isolation by the withdrawal method. Comparisons were made of the adsorptivebehavior of,,-tri-fluorooctadecylamine with that of octadecylamine and between,,-trifluorostearic acid and stearic acid. Much longer times of film formation were required by trifluorooctadecylamineto attain adsorption equilibrium than by the other three polar compounds. Hydrophobic monolayers of the fluorinated amine were isolated readily from aqueous solution but ap-plication of the same methods to the fluorinated acid was not successful. The introduction of the trifluoromethyl group caused a smaller decrease in the wettability than would have been expected from a comparison with the behavior of the perfluoroalkanoic acids. Monolayers of trifluorooctadecylamine were somewhat more wettable by organic liquids than were those oftrifluorostearic acid; also, whereas the former monolayer was hydrophobic, the latter was hydrophilic. Themechanism of adsorption of the film and the relation of the constitution of the film to its wettability are discussed. On the basis of both steric and electrical considerations, it is concluded that the introduction of the strong electric dipole associated with the CEVCHa-group is sufficient to offset or nullify the advantage initially expected to result from the introduction of the trifluoromethyl group.