Molecular Understanding on the Underwater Oleophobicity of Self Assembled Monolayers: Zwitterionic versus Nonionic
Molecular Understanding on the Underwater Oleophobicity of Self Assembled Monolayers: Zwitterionic versus Nonionic
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自组装单分子层水下疏油性的分子理解：两性离子与非离子
DOI：
10.1021/acs.langmuir.6b03988
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发表时间：
2017-02-21
期刊：
影响因子：
3.9
通讯作者：
Zhou, Jian
中科院分区：
文献类型：
--
作者：
Cheng, Gang;Liao, Mingrui;Zhou, Jian
采用分子动力学模拟方法研究了不同头部基团的自组装单分子膜的水下憎油性能。模拟结果表明，自组装膜的水下憎油能力大小顺序为甲基-lt；酰胺-lt；低聚乙二醇(OEG)<；乙醇胺(ETA)<；羟基<；混合带电两性离子。所有自组装膜的水下石油接触角均为143.6度；含有伯烷基铵离子的混合带电自组装膜具有较强的水化能力，可能具有最好的水下憎油性能。烷基磺酸盐阴离子(SO3-)比烷基三甲基铵离子(Nc3+)对氮原子上的疏水甲基具有更强的亲水性，且Nc3+能严重阻止混合带电自组装膜中SO3-的水化。若要在Nc3+/SO3--自组装膜中获得较好的水下憎油性能，则SO3-的单体长度应略长于Nc3+。此外，在低接枝密度下，自组装膜的水下憎油性能可能会变差。这项工作系统地证明了两性离子表面比非离子表面更具水下憎油能力。这些结果将有助于超疏油表面的设计和开发。
Molecular dynamics simulations are conducted to investigate the underwater oleophobicity of self-assembled monolayers (SAMs) with different head groups. Simulation results show that the order of underwater oleophobicity of SAMs is methyl < amide < oligo(ethylene glycol) (OEG) < ethanolamine (ETA) < hydroxyl < mixed-charged zwitterionic. The underwater oil contact angles (OCAs) are 143.6 degrees for all SAMs; mixed-charged SAMs containing primary alkyl ammonium ion are likely to possess the best underwater oleophobicity for its strong hydration capacity. It seems that alkyl sulfonate anion (SO3-) is more hydrophilic than alkyl trimethylammonium ion (NC3+) for the hydrophobic methyl groups on nitrogen atoms and that the hydration of SO3- in mixed-charged SAMs can be seriously blocked by NC3+. The monomer of SO3- should be slightly longer than that of NC3+ to obtain better underwater oleophobicity in NC3+-/SO3--SAMs. In addition, the underwater oleophobicity of SAMs might become worse at low grafting densities. This work systematically proves that a zwitterionic surface is more underwater oleophobic than a nonionic surface. These results will help for the design and development of superoleophobic surfaces.