Adsorption of thiocyanate ions to the dodecanol/water interface characterized by UV second harmonic generation

作者：Onorato Robert M; Otten Dale E; Saykally Richard J^*

来源：Proceedings of the National Academy of Sciences, 2009, 106(36): 15176-15180.

DOI：10.1073/pnas.0904800106

• buried interface
• Langmuir model
• nonlinear optics
• self-assembled monolayer
• surface spectroscopy

Recent experimental and theoretical results have firmly established the existence of enhanced concentrations of selected ions at the air/water interface. Ion adsorption to aqueous interfaces involving complex organic molecules is relevant to biology in connection with the familiar but incompletely understood Hofmeister effects. Here, we describe resonant UV second harmonic generation (SHG) studies of the strongly chaotropic thiocyanate ion adsorbed to the interface formed by water and a monolayer of dodecanol, wherein the Gibbs free energy of adsorption was determined to be -6.7 /- 1.1 and -6.3 /- 1.8 kJ/mol for sodium and potassium thiocyanate, respectively, coincident with the value determined for thiocyanate at the air/water interface. Interestingly, near 4 M and higher concentrations, the resonant SHG signal increases discontinuously, indicating a structural change in the interfacial region.

• 出版日期2009-9-8