Abstract
Ionic specificity effects, i.e., ions of the same valence leading to different macroscopic effects, are studied by considering a Langmuir monolayer of arachidic acid over a solution containing either or . We systematically vary levels as a way to control the interfacial surface charge and characterize the system by surface-sensitive x-ray scattering and spectroscopic techniques. We show that the critical surface pressure at the tilted () to untilted () transition is ionic specific and varies with . While the maximum density of surface bound per head group of arachidic acid is , the amount necessary to neutralize the surface charge, for it is nearly 0.6 and it is accompanied with a significant accumulation of the coions as revealed by surface x-ray spectroscopy. We account for the experimental observations by a statistical mechanical model including ion specificity.
- Received 8 September 2010
DOI:https://doi.org/10.1103/PhysRevLett.106.056102
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