Nature of amine-surfactant interactions at the air-solution interface.
Nature of amine-surfactant interactions at the air-solution interface.
复制标题
空气-溶液界面处胺-表面活性剂相互作用的性质。
DOI：
10.1021/la8024843
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Penfold J
中科院分区：
文献类型：
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作者：
Penfold J
聚乙烯亚胺(PEI)/十二烷基硫酸钠（SDS）的聚合物/表面活性剂混合物的表面张力和吸附行为强烈依赖于pH。在低pH和高pH下，PEI/SDS的强相互作用会导致表面聚合物/表面活性剂复合物的形成，从而在极低SDS浓度和界面处形成多层SDS时显著增强SDS的吸附。在低pH下，这种强烈的PEI/SDS相互作用主要是由两个带相反电荷的物质之间的静电吸引所主导。然而，在高pH下，PEI基本上是中性的，“疏水”相互作用的起源，或非静电起源的相互作用，不太清楚。为了进一步研究这种相互作用的起源，我们使用中子反射率和表面张力来研究不同阴离子表面活性剂SDS、十二烷基硫酸锂（LiDS）和十二烷基苯磺酸钠（LAS）在一系列小胺分子（从乙二胺到戊二胺）存在下表面吸附的pH依赖性。与在PEI/SDS混合物中观察到的类似，胺分子的存在诱导表面活性剂在低pH和高pH下的吸附，这可能导致在界面处形成多层的极端情况。在高pH下，吸附高度依赖于胺的分子量，当胺的分子量增加到五乙烯的分子量时，其吸附与在低pH下观察到的吸附相当。我们将这种在高pH下观察到的非静电相互作用归因于硫酸盐（或磺酸盐）头基与胺氮之间的偶极-偶极相互作用以及所附表面活性剂链之间的协同疏水相互作用的综合作用。在高pH值下，当存在至少六个胺基时，这种效应的强度似乎与低pH值下占主导地位的静电吸引力相当。这些结果对于理解PEI/表面活性剂相互作用的不寻常性质以及使用小分子量添加剂而不是大分子量聚合物来操纵吸附性能具有重要意义。
The surface tension and adsorption behavior of polymer/surfactant mixtures of polyethyleneimine (PEI)/sodium dodecyl sulfate (SDS) is strongly dependent on pH. At both low and high pH, a strong PEI/SDS interaction gives rise to surface polymer/surfactant complex formation that results in significantly enhanced SDS adsorption at very low SDS concentrations and in multilayer formation at the interface. At low pH, this strong PEI/SDS interaction is dominated by the electrostatic attraction between the two oppositely charged species. However, at high pH the PEI is essentially neutral, and the origin of the “hydrophobic” interaction, or interaction of nonelectrostatic origin, is less clear. To investigate the origins of this interaction further, we have used neutron reflectivity and surface tension to study the pH dependence of the surface adsorption of different anionic surfactantsSDS, lithium dodecyl sulfate (LiDS), and sodium dodecyl benzene sulfonate (LAS)in the presence of a range of small amine molecules (from ethylenediamine to pentaethylenehexamine). Analogous to that observed in PEI/SDS mixtures, the presence of amine molecules induces a strong enhancement in the surfactant adsorption at both low and high pH, which can result in extreme cases in multilayer formation at the interface. At high pH, the adsorption is highly dependent upon the amine molecular weight and is equivalent to that observed at low pH by the time the molecular weight of the amine has increased to that of pentaethylenehexamine. We attribute this nonelectrostatic interaction observed at high pH to the combined effect of a dipole−dipole interaction between the sulfate (or sulfonate) headgroup and the amine nitrogens and a cooperative hydrophobic interaction between the chains of the attached surfactants. At high pH and when there are at least six amine groups present, this effect appears to be equivalent in strength to the electrostatic attraction that dominates at low pH. These results are significant in the context of understanding the unusual nature of the PEI/surfactant interaction and of using small molecular weight additives rather than much larger molecular weight polymers to manipulate adsorption properties.