Cation Selectivity at Air/Anionic Surfactant Solution Interfaces

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• 作者：Vanessa E. Haverd and Gregory G. Warr
• 刊名：Langmuir
• 出版年：2000
• 出版时间：January 11, 2000
• 年：2000
• 卷：16
• 期：1
• 页码：157 - 160
• 全文大小：48K
• 年卷期：v.16,no.1(January 11, 2000)
• ISSN：1520-5827

文摘

The selective binding of alkali metal and quaternary ammonium ions to anionic surfactant films at theair/solution interface has been investigated using the ion flotation technique. Surfactant anions studiedwere the dodecyl phosphate monoanion, the hexadecyl phosphate dianion, bis(2-ethylhexyl) phosphate,dodecanoate, and dodecyl sulfate. Alkali metal ions display only weak selectivity at adsorbed films of allsurfactants studied. The binding strength increases in the order Na⁺ < K⁺ < Rb⁺ < Cs⁺, with the exceptionof films of dodecanoate, for which the ions have equal affinity, and the hexadecyl phosphate dianion, forwhich the selectivity sequence is Cs⁺ < Rb⁺ < K⁺ < Na⁺. By contrast, the binding of quaternary ammoniumcounterions to adsorbed films of anionic surfactants has a striking dependence on the surfactant headgroup.Results are interpreted using a model which includes solvation of the headgroups and competing counterionsand is compared with competitive binding of phosphate, sulfate, and acetate ions at cationic surfactantfilms.