期刊
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
卷 14, 期 41, 页码 9285-9290出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.3c01530
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In this study, we investigated the influence of sodium chloride (NaCl) on the interface properties of water and dodecyl sulfate (DS-) surfactant using vibrational sum-frequency generation spectroscopy. We observed a highly nonlinear dependence of the O-H stretch vibrations of oriented water molecules on the NaCl concentration at the interface. This nonlinear dependence can be explained by the screening effects of the electric field of surface-bound DS- ions and the Coulomb repulsion between the headgroups of DS- ions in the surface plane. Within a limited concentration range of NaCl (10-100 mM), the latter effect significantly increased the signal of oriented water, indicating a two-dimensional hydrophobic collapse of the surfactant layer.
We study the effect of sodium chloride (NaCl) on the properties of the interface of water and the surfactant dodecyl sulfate (DS-) using heterodyne-detected vibrational sum-frequency generation spectroscopy. We find that the signal of the O-H stretch vibrations of oriented water molecules at the interface is highly nonlinearly dependent on the NaCl concentration. This nonlinear dependence is explained by a combination of screening of the electric field of surface-bound DS- ions pointing into the bulk and screening of the Coulomb repulsion between the headgroups of the DS- ions in the surface plane. The latter effect strongly increases the oriented water signal within a limited NaCl concentration range of 10-100 mM, indicating a two-dimensional hydrophobic collapse of the surfactant layer. The occurrence of collapse is supported by model calculations of the surface potential and surface surfactant density.
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